(up to half Yearly Exam)
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0. Language Of Chemistry 1. Crop Production 4. Metals and Non- metals 5. Fuels and Combustion 6. Wood Coal and petroleum 7. Biodiversity and its conservation 8. Cell Structure and Function 11. Force and Friction 12. Pressure 13. Sound 18. The universe
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Language of Chemistry Questions & Answers
Back to contents
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(i)
Element. Simple forms of matter which cannot be
decomposed
into
simpler
substances
are
called
elements. Example- hydrogen, oxygen, iron, silver, etc.,
(ii) Compound. A compound is a substance produced by union of two or more elements in a definite proportion. It can be decomposed
into two or more simple
substances. Example Water and carbon dioxide.
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(v) Radical. The molecule of a compound is usually made up of two parts which are separately known as radicals. For example, the radicals present in
sodium chloride
molecule
while
potassium
are
sodium
nitrate
and are
chloride potassium
and
those
in
nitrate.
electronegative radicals.
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(i) Acid Radical - When an acid reacts with a base,
a
salt
is
produced
as
a
result
of
neutralization.
In the molecule of sodium chloride its chloride
radical has been contributed by hydrochloric acid and is, therefore, termed as Acid Radical. In the case of inorganic salts,
the metallic
radicals nitrate, sulphate and carbonate are called acid radicals. 9
(ii) Basic Radical - When an acid reacts with a base,
a
salt
is
produced
as
a
result
of
neutralization.
In the molecule of sodium chloride the sodium radical has been contributed by the base sodium hydroxide and is, therefore, called Basic Radical.
In the case of inorganic salts,
the metallic
radicals of the type of sodium are called basic radicals
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(iii) Simple radical - A radical is called a simple radical when it in as atom only, e.g., sodium, potassium etc. (iv) Compound radical - It is known as a compound radical when it is made up of a group
of two or more different atoms, e.g., nitrate— made up of one nitrogen atom and three oxygen atoms and sulphate–made up of one sulphur atom and four oxygen atoms. compound radical can be introduced or expelled from combination without change. 11
(v) Electro-positive radicals - When a salt is dissolved
in
constituent
water,
it
splits
up
into
the
radicals. The basic radicals then
carry a positive charge (positive because of this reason,
ions) and are,
termed electro-positive
radicals. (vi) Electronegative radicals - When a salt is dissolved
in
constituent these
water,
it
splits
into
the
radicals. The acid radicals under
circumstances
carry
(negative ions) and are called
radicals.
up
negative
charge
electronegative 12
The molecular weight of an element or a compound is defined as
the relative weight
of
its
molecule as
compared with that of carbon atom (12C isotope) taken as 12 amu. It is only a number and gives only a relative
weight of the molecule. It
does not give us the actual
weight of the molecule at all. Molecular weight of magnesium carbonate is equal to 84 times that a
molecule of magnesium carbonate is 7 times heavy as an atom of carbon or 84 times as heavy as onetwelfth of an atom of carbon
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4. What is a symbol? What information does it
convey? A symbol is the short form which stands for the atom of a specific element or the abbreviations used for the names of elements.
1.It represents a specific element. 2.It represents one atom of an element. 3.A symbol represents how many atoms are present in its one gram (gm) atom.
It represents the number of times an atom is heavier than one atomic mass unit (amu) taken as a standard 14
5. Why is the symbol S for sulphur, but Na for sodium and Si for silicon? In most cases, the first letter of the name of the
element is taken as the symbol for that element and written in capitals (e.g. for sulphur, we use the symbol S). In cases where the first letter has already been adopted, we use a symbol derived from the
Latin name (e.g. for sodium/Natrium, we use the symbol Na). In some cases, we use the initial letter in capital together with a small letter from its name (e.g. for silicon, we use the symbol Si
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6. If the symbol for Cobalt, Co, were written as CO, what would be wrong with it?
Co stands for Cobalt. If we write CO, then it would mean that it is a compound containing two non-metal ions, i.e. carbon and oxygen, which forms carbon monoxide gas.
7. What do the following symbols stand for – (a) H, (b) H2 , (c) 2H and (d) 2H2 (a) H stands for one atom of hydrogen. (b)
H2
stands
for
one
molecule
of
hydrogen.
(c) 2H stands for two atoms of hydrogen. (d) 2H2 stands for 2 molecules of hydrogen 16
8. Write the full form of IUPAC. Name the elements
represented by the following symbols: Au, Pb, Sn, Hg The full form of IUPAC is International Union of Pure and Applied Chemistry. Names of the elements: Au – Gold
Pb – Lead Sn – Tin Hg – Mercury
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9. Define Valency? Valency is the number of electrons an atom can donate or accept to form a chemical bond with
another
atom.
Or
Valency
is
defined
as
the
combining capacity of an atom of an element. 10. Explain Variable Valency. It is the combining capacity of an element in which
the metal loses more electrons from a shell next to a valence shell in addition to electrons of the valence shell.
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11. What is monovalent; divalent and as trivalent element? An element with a valency 1 is said to be monovalent; with a valency 2 as divalent and
with a valency 3 as trivalent. 12. What are the types of compounds Atoms of different elements join together in definite
proportions
to
form
molecules
of
compounds. Compounds can be either ionic compounds or molecular compounds. 19
13. What is ionic compounds? Ionic compounds are those compounds that contain charged species of metals and non metals. The charged species are known as ions. An ion is a
charged particle and can be negatively or positively charged. A negatively charged ion is called an anion and
the
positively
charged
ion
is
called
a cation. Ionic compounds are formed when ionic
bonds
are
formed
between
different
elements
through the transfer of electrons. Examples of ionic compounds — sodium chloride, calcium oxide. 20
14. How we name a positive ion or cation and negative ion or anion
To name a positive ion or cation, first write the name of the parent element and the word ‘ion’ is added in the end. For example, Sodium (Na) atom on losing an electron, becomes sodium ion (Na+)
and Calcium (Ca) atom on losing two electrons, becomes calcium ion (Ca2+).
To name a negative
ion or anion, write the name of the parent element by changing its end
to –ide and the word ‘ion’ is
added in the end. For example, Oxygen (O) atom on gaining two electrons becomes oxide ion. 21
15. What is electronegativity ? Electronegativity is a chemical property that describes the ability of an atom to attract electrons towards itself in a covalent bond.
16. What is meant by atomicity? Name the diatomic element. Solution: The number of atoms of an element that join together to form a molecule of that element is known as its atomicity. Diatomic molecules: H2, O2, N2, Cl2 22
17. What is Molecular compounds.
Molecular compounds or covalent compounds
are those compounds in which the elements share electrons via covalent bonds. Examples — water, ammonia, carbon dioxide.
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18. Explain formulae of Compounds
The number of atoms of elements present in one molecule of a compound is represented using the chemical symbols of its constituent elements,
which is called a chemical formula. For example, one molecule of water is represented as H2O, which means one molecule of water contains 2 atoms of hydrogen and 1 atom of oxygen. Just as elements compounds
are are
represented represented
by
symbols,
by
chemical
formulae. 24
19. What are monoatomic and polyatomic ions ? Give two examples of each.
Examples. Monatomic Ions: Examples for monatomic ions include Na+, K+, Cl–, etc. Polyatomic Ions: Examples for polyatomic ions include NH4+, NO2–, NO3–, etc.
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20. What is a chemical formula ? What does it represent ?
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21. What information do we get from a chemical equation
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22.
What
are
exothermic
and
endothermic reactions.
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23.
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24. How are symblos of elements derived?
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32
25.
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26. What are ions? How are postive and negetive ions are named?
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27. Write the step by step procedure for writing the molecular formula of compunds..
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28. Explain the reactant and product of a chemical equation.
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29. Explain the need of balancing a chemical equation? What information are conveyed by a balanced chemical equation.
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30.What
are
the
limitations
of
chemical
equations?
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42
Element Symbol
Atomic Number (Z)
Mass Number (A)
Protons Neutrons Electrons (Z) (A-Z) (A)
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Element Symbol
Atomic Number (Z)
Mass Number (A)
Protons Neutrons Electrons (Z) (A-Z) (A)
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48
49
50
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53
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Back to contents 55
1. Why it becomes necessary to prepare the soil for growing a crop?
The soil acts as a medium for the germination of seeds and the growth of crops. It provides water and minerals to the plants. The growth of plants depends on the fertility of the soil. Different kinds
of plants require different kinds of soil. Therefore, it becomes necessary to prepare the soil for growing a crop.
2. Why earthworms are also known as nature ploughshare? Earthworms are also known as nature ploughshare . Their habit of burrowing and swallowing earth below the upper surface increases the soil fertility. Actually, they are continually manuring and ploughing the soil. Their burrows permit the penetration of air and
moisture into the porous, improve drainage and make the downward growth of the roots easier . Their excreta and their secretion enrich
the soil by adding nitrogen is matter to it. Their burrowing habit also helps in mixing and churning the soil. 56
3. What are the activities involves in soil preparation? What are the benefits of soil preparation?
The preparation of soil involves loosening and turning of soil. It has the following benefits –
• The loose and soil allows the roots to penetrate deeper with ease. • It improves the air circulation within the soil, allowing the roots to
breathe easily even when they are deep. • The roots, in turn, anchor the plants more firmly in the soil. • The loosened soil also aids the growth of earthworms and microbes
present in the soil. These are called farmer's friend as the aid n further turning and loosening of the soil and also increases its
fertility. • Loose soil gets mixed with the fertilizer more uniformly.
• Turning of soil uproots the undesirable plants growing in the field. • It also enhances the water retaining capacity of the soil. • Loosening and turning of soil brings the nutrient rich soil on the top. This nutrients are then used by the plants easily.
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4. What is Ploughing?
The process of loosening and turning the soil is called tilling or ploughing. This is done with the ploughs. In earlier times, ploughs were made of stones, bronze or iron. Now ploughs made of iron or
wood are used for tilling. 5. Before sowing the seeds, what is to be done for better
productivity? Before sowing the seeds, the soil is made porous for better productivity. 6. What are the main tools used for ploughing ? Some of the main tools used for ploughing are –
(a) Plough - It is used for tilling of soil, adding fertilisers to the crop, removing the weeds, scraping of soil.
(b) Hoe - It is used for removing weeds and for loosening the soil. (c) Cultivator - Used for ploughing. 58
7. What is the use of plough? Describe the various parts of plough. Can it be operated manually?
Plough has been in use in agriculture for tiling, removing weeds and scrapping of soil. This is made of wood and is drawn by a
pair of bulls. It consists of a triangular iron strip called ploughshare. There is a long shaft of wood called plough shaft which has a handle at one end. The other end of the shaft is
attached to a beam which is hung on the bull’s neck. This plough can be easily operated by a single man and, thus, used manually.
8. What is the use of hoe? Describe the various parts of hoe. Hoe is a simple tool used for removing weeds and, loosening and breaking the lumps of soil. It also has a long rod of wood or iron.
A strong, broad and bent plate of iron is fixed to one of its ends, which works like a blade. The other end of has a beam which is pulled by blocks. 59
9. What is the use of cultivator ? How cultivators are operated? What is a tractor?
Large fields are ploughed with the help of tractor driven cultivators with multiple numbers of ploughshares. Tractors are motor vehicles with heavy tread tyres. These are used to pull farm machinery. This shaves labour as well as time. 10. Why the crop field are tilled and labelled?
Ploughing of dry soil results in the formation of large soil crumbs , which are further broken down by a soil plank. The tilled or ploughed land is then labelled with the help of a wooden
or iron-leveller. This prevents a erosion of the soil by wind water. Sometimes, manure is added to the soil added to the soil before
tilling. This helps in the proper mixing of manure with the soil. Once the soil is tilled and levelled,
it is ready for sowing of
seeds. 60
11. What is sowing?
Sowing is a process of putting seeds in the soil. Why Selection of seeds is important before sowing? How farmers prevent onset of disease.
Before showing , the selection of
high- yielding varieties of
seeds is very important.•
The seeds should healthy and of good quality.
•
Diseased and low quality seed reduce crop productivity in terms of both quantity and quality.
•
Also, if infested seeds are sown in the crop fields, pests may be emerge out of these seeds which may infest the crops and damage them completely.
Nowadays, farmers wash the seeds with fungicide solution to prevent onset of disease.
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12. Two handful of wheat grains are stored for more than 10 months. After that, these are put in a beaker containing water for 5 minutes.
What will be observed after 5 minutes? Explain you answer. It will be observed that some seeds float, while others settle at the bottom. A few seeds are hollow and light because they are infested
or eaten by pests. As a result, they float on the surface of water. The healthy seeds are very heavy and sink to the.
13. How seeds are sown in the crop field? Seeds can be sown manually or by using seed drills. 14. What is known as broadcasting? Why this method is not considered good? Also, a few seeds like bajra and maize are sprayed in the field
instead of
being put in the soil. This process is known as
broadcasting.
This method is not good because it does not get
proper spacing or depth. Moreover, the seeds are picked up at it and eaten by birds. 62
15. What is seed drill? How it is operated? What are the advantages of using it?
A seed drill is a long metal tube with a funnel at the top. It is tied at the back of the plough. As the plough makes the furrows in the soil, the seed drill release the seeds into the furrows and
sown them. Drills have 5-6 metals pipes with a with common funnel at the top. These drills are driven by the bullocks or by
tractors and can sow the seeds in 5 to 6 rows simultaneously. Sowing by traditional tools by seed drill is a easiest method. The seeds sown with the drills are always in rows. This prevents the
damage caused by the birds, and saves time and labour.
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16. How paddy and many vegetables such as tomato, onion and
chilli are sowing in the field? What is its advantages? The method of sowing used in the case with paddy and many vegetables such as tomato, onion and chilli are different. Their
seeds are not directly sown in the crop fields. Instead, they are first sown in a small plot or nursery. These are allowed to grow
into small plants called seedling. From these, healthy and diseasefree seedlings are selected and transplanted in the field manually. Transplantation
enables
to
select
better
seedlings.
It
also
promotes deeper penetration of roots, which helps to increase the crop productivity.
17. What is seedling? The seeds of paddy and many vegetables are not directly sown in
the crop fields. Instead, they are first sown in a small plot or nursery. These are allowed to grow into small plants called seedling. 64
18. What precautions are to be taken while sowing? •
Seeds should be planned at a proper depth in the soil. If seeds
are planted deep, they may not germinate due to nonavailability of moisture as well as air. The seeds if planted on the surface are eaten up by the birds. •
Seeds must be sown leaving appropriate distance between them. This is important to avoid overcrowding of crop plants.
Otherwise, the plants will not get sufficient sunlight, nutrients and water from the soil. Proper sowing also prevents wastage of space in the field. Seed drills automatically regulate this
distance between the seeds.
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19. Three container/ pots/ empty glasses A, B, C filled with half soil. A little amount of urea and cow dung manure are added in A and B respectively. Nothing has been added to C. These are watered and same sized seedlings are planted in them. Then they are watered
regularly. What will be observed in the growth of the plant in a week? Can you give reasons of the observations?
Followings are observedPlant A shows maximum growth. Plant B shows good growth but less than that in ‘A’. Plant C shows least growth. Fertilizers are rich in nutrient needed by the plant. So, it gives the
maximum growth to the plant. Cow dung manure also contain the nutrient. But, this is lesser in
comparison to urea. As a result we see better growth than plain soil but lesser than what we get with urea. Since container C contains plain soil, is not added with any additional nutrient it has least growth.
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20. What are termed as fertilizers or manure? What is manuring?
You have studied in the previous classes that plants require certain minerals that are essential for their growth. These are obtained from the soil for their growth. Every crop utilise a certain
specific nutrients for its growth. Therefore, continuous growing of the same crop in a field makes the soil deficient in certain
nutrients. So, these nutrients need to be replenished from time to time. Otherwise, the soil would become infertile, barren and incapable of supporting plan growth any further. Thus, farmers add specific nutrients in the field to replenish soil. These nutrients are termed as fertilizers or manure and the process is called
manuring. 21. What are the advantages of using fertilizer?
Fertilizers are easy to store and handle as they come in packets and bags. Fertilizer are soluble in water and ,thus, are directly absorved by the plants, increasing the yield. 67
22. What are Fertilizers? Fertilizers are man made artificial chemical compounds rich in inorganic
nutrients.
They
provide
specific
nutrients
like
nitrogen(N), potassium (K) and phosphorus(P) which are not obtained from manures. These fertilizers are also called NPK fertilizers. Some other examples are urea, potash, ammonium
sulphate, etc. 23. Why fertilizers are also called as NPK fertilizers?
Fertilizers are chemical compounds rich specific nutrients like nitrogen(N), potassium (K) and phosphorus(P) , this is the why fertilizers are also called NPK fertilizers.
24.
Why
farmers
uses
a
combination
of
manures
and
fertilizers?
A farmer uses a combination of manures and fertilizers to improve the crop yield. 68
25. Why nowadays emphasis is given on to increase the use of organic fertilizers or manures? Though the use of chemical fertilizers has increased the yield, their excessive use has made the soil less fertile and has even polluted the
water sources. Due to these reasons, nowadays, the emphasis is given on increasing the use of organic fertilizers or manures.
26. What is manure? Manure is an organic substance obtained from plant or animal wastes,
such as cow dung , urine , plants parts, vegetables or fruit peels, night soil and other similar organic wastes. 27. What composting? Wastes, such as cow dung , urine , plants parts, vegetables or fruit peels, night soil and other similar organic wastes are dumped at open places or
pits and covered with soil and allowed to decompose. The decomposition is helped by organisms like bacteria and fungi. The decomposed matter
is used as a manure. This process is known as composting. 69
28. What is compost? How it is formed?
Compost is an organic manure formed by burying dead plants and animal wastes in a pit. These wastes are covered with a layer of soil or mud and are left undisturbed for rotting. Sometimes, water is added to the pit to facilitate decomposition. Bacteria and fungi in the layers of soil or speed up the decomposition. The compost, thus formed, is rich in organic nutrients and is used in fields. 29. Why manure is considered better than the chemical fertilizers?
Organic manure is humus-rich and considered better than chemical fertilizers because it
•
Food
crops
grown
by
using
manures
are
safer
for
human
consumption than the crops grown with the help of chemical
fertilizers. •
Adds organic nutrients to the soil.
•
Increases the water holding capacity of the soil .
•
Enhances the number of friendly microbes.
•
Improves the texture and chemical nature of the soil. 70
30. What is known as organic farming Farming that utilizes organic manure is known as organic farming. 31. What is vermi-composting? Use
of
earthworms
for
preparing
compost
is
called
vermi-
composting. Certain species of earthworms are suitable for vermicomposting and are procured from certain specific agencies . 32. What are the natural methods of replenishing the soil? Field fallow, crop rotation and mixed cropping are three natural methods of replenishing the nutrients of the soil.
33. What is field fallowing? It is the process of leaving the field uncultivated for one or more
seasons. This helps in replenishing
the lost nutrients naturally
because during this time, dead plants, animals and other organic matter get collected on the field. This collected matter gets
decomposed by the microbes and add nutrients to the soil. 71
34. What are the differences between fertilizer and manure? S. No 1
Fertilizer
Manure
It is an organic man made Manure
is
a
natural
chemical compound or a substance formed by the salt
decomposition
of
the
animal and plant waste 2
It is prepared artificially in It can be prepared in the factories
3
fields by farmers
It does not provide any It is rich in organic matter
humus to the soil as to and provides a lot of humus poor inorganic nutrients 4
It
is
rich
nutrients
in
like
to the soil
inorganic It is comparatively less rich
nitrogen, inorganic nutrients
phosphorus and potassium 72
35. What is known as crop rotation ? Another method of replenishing the soil with nutrients is to grow different crops alternately so that the soil is not depleted
of one particular nutrient. This is known as crop rotation. 36. Why in North India, farmers grow legumes and wheat
alternately? This is an example of crop rotation. In North India , farmers grow legumes and wheat alternately. This is because wheat
uses up large amounts of nitrogen from the soil . This nitrogen can be replenished in the soil when legumes are grown there.
37. How legumes can fix atmospheric nitrogen? Legumes can fix atmospheric nitrogen through the bacteria
Rhizobium present in their root nodules. The atmospheric nitrogen is converted into nitrates , which replenish the soil with usable nitrogen 73
38. If you visit an agricultural field and meet a farmer and had a
discussion with him, what you will try to find out ? •
the types of manures and fertilizers used by him.
•
The difficulties faced by him employing these methods and
•
his knowledge of other advanced methods to raise productivity.
39. What is mixed cropping ?
Sometimes farmers grow two or more crops together in the same field. These crops help in the growth of each other by maintaining the nutrients
in the soil ; for example, groundnut and cotton crops are often brought together for better productivity.
40. What is irrigation ? Plants needs water for seed germination, absorption of nutrients from the soil, their growth and preparation and storage of food. If they are not watered regularly, the plants droop. In fact, in summers, plants require more water than in winters because of the evaporation of water from the
soil and the plant surface. Therefore, it is necessary to supply water to plants in a fields periodically. This is known as irrigation . 74
41. What will happen if there is insufficient or excess supply of water to the crops?
In both cases the crops may get damaged. When water is insufficient, the crops do not get enough water and, thus, wilt. On the other hand, if water is in excess, it gets collected in the field, which reduces air in the soil. As a result, the supply of air to the roots is reduced, resulting in the decreased
growth of plants. Moreover, the evaporation of water from the waterlogged fields increases the amount of salt in the soil. This decreases the fertility of the soil further affecting the
growth of the crops. Thus , a field needs to be irrigated with just the right amount of water.
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42. What are the factors that influence the irrigation needs of fields?
Irrigation needs of fields are influenced by the type of soil, nature of crop and the season. 43. How type of soil influence the irrigation needs? •
In a sandy soil,
more water is required because of fast
percolation and less water retaining capacity.
•
The clayey and black soils have more water retaining capacity and , thus , they require less water. Therefore, these soils have
more chances of water logging than the sandy soil. 44. How good harvest depends on monsoon? The major source of water in the field is rainfall. Since the time and
amount of rainfall fluctuates, the crop yield also fluctuates. The timely monsoon results in a good harvest,
while a delayed or no
monsoon spoils the crop yield completely. 76
45. Why farmers depend on the alternate source of irrigation?
What are the alternate source of irrigation? The major source of water in the field is rainfall. Since the time
and
amount
of
rainfall
fluctuates,
the
crop
yield
also
fluctuates. Therefore , farmers depend on the alternate source of irrigation. These
sources are rivers , reservoirs , lakes ,
ponds wells and tube wells . 46. How waters are used for irrigation form the alternate sources?
From the alternate source of irrigation, these waters are either pumped by using electric pump or diesel pumps or delivered
via irrigation canals.
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47. How modern irrigation methods are works? What is the advantage of modern irrigation methods over traditional methods. In
modern
irrigation
methods,
powerful
motor
pumps
are
commonly employed for drawing water for irrigation. These pumps can be used for lifting water from wells , streams , canals, ponds or lakes. These pumps are run on electricity, diesel or solar
energy, and are available in different sizes and capacities. Pumps are commonly employed to draw water from deep narrow wells
called tube wells . Advantages•
Modern irrigation methods are more efficient than traditional
irrigation methods. •
Using
tube
wells
and
motor
pumps,
two
important
improvements have been in use for last few years. These newer
methods use water in an economical way and prevent wastage. 78
48. Describe sprinkler system of irrigation.
This method is useful in water scares areas such as sandy soil and where there is a less or uneven rainfall. It consists of main pipe, which is attached many pipe in series. These perpendicular pipes have nozzles (which are usually of rotating type) at right angles. Water flows through the top of the main pipe. With the help of pump, water enters
into the attached pipes and comes out the forms of sprinkle through the nozzle and falls on crops like rain. This method uses much less
water than the conventional methods of irrigation. 49. Describe drip system of irrigation. This technique is used for watering fruit plants, gardens and trees. The drip system consists of a water pump attached to the main pipe , which further has lateral pipes attached to it. These lateral pipe have
this small nozzles which are located just near the roots of the plants. When water flows through the system, it falls drop by drop at the
position of the roots. This is useful in areas where water is not available in large quantities.
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50. What is called lodging?
Sometimes,
untimely
rains
and
hailstorms
or
fast
wind
accompanied by rain damage the crops. In case of wheat, maize,
paddy and a few others, these winds and rain at the grain maturation stage, result in fall of crop plants. This is called lodging.
51. What are weeds? Give some examples of weeds. Sometimes some other plants are growing along with the desired plants. These unwanted plants are called weeds.
A few example of weeds are Parthenium (carrot or congress grass), Amaranthus, Chenopodium , grasses and wild oat.
52. What is weeding? The process of removing weeds from a field is called weeding.
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53. Why is it important to remove weeds from the crop field?
Or Why weeding is necessary? There are a variety of weeds that grow with different plants. They vary from place to place and from season to season. Weeds are undesirable plants because weeds compete with the crops for
water, mineral, sunlight and space. they deprive the desired plants of crops from sunlight, water, nutrients and space as they spread
very fast . They affect the growth of the crop, reducing the yield. Some weeds interfere with the harvesting of crops. Weeds may be poisonous for animal as well as for human being use. It is thus
important to remove them from the field. 54. How insects are use to control weeds?
There are certain insects that feed on specific weed. This insects are used to control weeds as they are safer than chemical weedicides. 81
55. What are the ways adopted by the farmers to remove weeds and control their growth before they produce flowers and seeds?
Describe them in details. The ways adopted by the farmers to remove are •
Manual removal - The weeds can be removed manually by pulling or cutting them close to the ground from time to time. This is done with the help of a trowel (khurpi) or a harrow.
Weeding should be done carefully as it may damage the crop plants or even uproot them. The removed weeds dry up, get the decomposed and mix with the soil.
•
Use of chemicals - weeds are also controlled by using certain chemicals called weedicides or herbicides. These are sprayed
in the fields with a sprayer. This chemical kills the weeds but do not harm the crops. Weedicides should be sprayed before the weeds develop flower and seeds. 82
56. Why spraying of weedicides or herbicides should be done with a
lot of precaution? Why grains must be properly washed before being consumed. Before spraying , the weedicides are diluted with water. The amount of dilution depends upon the crop on which these are to be sprayed. Spraying should be done with a lot of precaution as weedicides
contains certain chemicals and these may be poisonous and it may affect the health of the farmers and animals. Therefore, the grains
(of the crop) must be properly washed before being consumed. 57. Give some examples of weedicides? Some common weedicides are dalapon, metachlor , 2, 4-D and siniazine. 58. What are natural herbicides or bioherbicides?
The harmful chemical weedicides are now a days being replaced with other chemicals called natural herbicides or bioherbicides.
These are derived from microbes or specific plants and are not harmful to organisms, including human beings.
83
59. How some organisms destroy crops? The crops in an open field are exposed to several organisms which may destroy them. A few examples are given below.
•
Stray animals can damage the crop.
•
Rats often damage and consume a larger portion of grain
produced. •
Birds eat and destroy grains of standing crops.
Insects are the greatest enemies of crops. They damage crops
at every stage of the life cycle. They damage not only the standing crops but also the stored grains.
60. What are pests? How pests are responsible for loss of output in crop production? All organism which cause damage to crops and make them unfit
for human consumption are referred to as pests. Pests are responsible for up to 30% loss of output in crop production. 84
61. What are pesticides? Various poisons chemicals are used to kill the pastes in a field.
They are called pesticides 62. What are Rodenticides? Give an example.
Rodenticides are use to kill rodents such as rats, example warfarin. 63. What are Insecticides? Give an example. Insecticides are used to kill eggs, larva and adults of insects,
example DDT. 64. What is the full from of DDT?
The full from of DDT is Dichlorodiphenyltrichloroethane (DDT). 65. How pesticides are sprayed on the crops fields. Pesticides are sprayed on the crops in a field manually by handoperated machine in the small field and by low-flying aircraft in case the fields are large.
85
66. What are the different methods employed by farmers to protect
their crops? Different methods employed by farmers to protect their crops are•
The crops are protected from stray animals by raising wire fences and mud walls around the fields.
•
The bird can be scared off beating of drums and installing
scarecrows. •
Plants are also damaged by disease caused by viruses, fungi
and bacteria. Spraying certain chemicals protect the plants from this organisms. •
Various poisons chemicals are used to kill the pastes in a field.
They are called pesticides. These include(i)
Rodenticides which are use to kill rodents such as rats,
example warfarin. (ii) Insecticides which are used to kill eggs, larva and adults of insects, example DDT 86
67. Why great care should be taken while using pesticides? •
Pesticides should be sprayed at the appropriate time as their effective only at a particular stage of the pest’s lifecycle.
•
The dosages of the pesticide should be correct and specific, otherwise
the
pasts
might
become
resistant
to
these
chemicals. •
The pesticides should be chosen in such a way that they do not harm human beings and non-targeted organisms.
•
Pesticides may stick to fruits and leafy vegetables. Therefore, theses should be thoroughly washed before consumption.
•
Pesticides generally get washed down to the soil and are absorbed by the plants, which means that they enter the food chain. This may accumulate in your body and cause various
diseases. Therefore, it is advisable to replace the pesticides with others safer methods. 87
68. Describe the process of storage of produce?
In this process, the grains are packed in suitable containers. Farmers use small mud or metal containers (beans) to store grains for their own use. The remaining produce is sold to the
government and private agencies for further distribution or use. The large amounts of grains are stored in the granaries and silos. Grains are weighed into jute bags, called gunny bags and
transported to go-downs. 69. What is buffer stock?
In practice, an extra stock called buffer stock, is always maintain so the grains are available in plenty even if there is a shortfall in a production in a particular year.
70. What is last but an important task in crop production? Storage of produce is the last but an important task in crop
production. 88
71. Name the different structures used for safe storage of grains?
The large amounts of grains are stored safely in the granaries and silos. 72. Why do we need to store grains properly?
These grains need to be transported and stored properly as they were harvested once a year. During storage, these are
protected
against the attack of different pests and microorganisms. 73. In a cold storage or a go-down which points needs to be checked? Following points needs to be checked in a cold storage or a go-down where grains have been stored.
•
The types of grains stored.
•
The conditions of storage, temperature, etc.
•
Various procedures followed to protect grains from paste.
•
The methods of transportation and distribution. 89
74. How do farmers protect their crops from pests? •
Before storage, excess moisture in the food grains is removed by drying them in the sun.
•
Grains are kept at a lower temperature for preventing the growth of microorganisms.
•
Sometimes, stored grains in go-downs are sprayed with
suitable chemicals to avoid paste attack. •
The population of rats in the Go-down is kept under check
with the use of rat poison from time to time.
90
91
92
93
Harvesting of crops the process of cutting and gathering of crops from the fields after the crops and maturity is called harvesting of crops. Harvesting can be done by the
following methods•
Farmers use sickles to manually harvest crops, especially wheat, Maize and paddy
•
The tractor driven machine called harvesters also used for harvesting wheat and paddy in
large fields. •
Fruits and vegetable are plucked manually by the farmers 94
Back to contents 95
1. What are the physical properties of metals? •Metals, in their pure state, possess a shining surface (metallic
lustre), •Metals are generally quit hard and strong, •Metals are solids at room temperature, •Metals have high melting and boiling points, •Metals are good conductors of heat,
•Metals are good conductors of electricity, •Metals are sonorous, •Metals are usually malleable,
•Most of the metals have a high tensile strength, •Metals have high densities.
2. Which are the most malleable metals? Gold and silver are the most malleable metals. 96
3. Why ornaments are made of gold and silver. Gold and silver have the following physical properties which
make them suitable for making ornaments •
very high metallic lustre.
•
Most
malleable
metals
and
can
be
easily
obtained
by
hammering small pieces of metals. •
Most ductile metals and therefore they can be drawn into
chains. 4. How iron articles of various shapes are prepared?
Iron articles of various shapes are prepared by hammering hot iron. 5. What are the uses of Aluminum foils?
Aluminium foils are used tour wrap chocolates, cigarettes. Medicines, foodstuffs and to seal bottles.
97
6. Why Aluminium foils are used to wrap chocolates, cigarettes. Medicines, foodstuffs and to seal bottles etc?
The malleability of Aluminium is very high, therefore its foils are used to wrap chocolates, cigarettes. Medicines, foodstuffs and to seal bottles.
7. What is ductility? Ductility is a physical property of metal due to which it can be
drawn into wires. 8. Why Copper and Aluminium wires are used for making electrical cables.
Copper and Aluminium have high ductility due to which the can be drawn into wires. Due to this property they are used for making electrical cables. They are second and third low-cost conductors
of
electricity
respectively. Silver is
the best conductor of
electricity but it is costlier. 98
9. Which are the most ductile metals ? Gold and silver are the most ductile metals followed by Copper
and Aluminium. 10. What is meant by high tensile strength? high tensile strength is a physical property of some metal due to
which they can hold heavy loads without breaking 11. Which metals float on water surface? Why?
Sodium and potassium metals have low densities due to which they float on water surface. 12. What is meant by sonorous?
Some metals have physical properties due to which they make a ringing sound when struck. 13. Which metals is commonly used for making Temple Bells?
Why? Bronze have very is sonorous metals and there are commonly
used for making Temple Bells.
99
14. What is malleability? Some metal have the physical property that they can be
hammered into thin sheets and rolled into different shapes without breaking. 15. Which metals are preferred for making cooking vessels and water boil? Silver followed by copper and aluminium are the best conductor of
heat. Therefore cooking vessels and water boilers are made of Copper and Aluminium. Sodium, potassium, gallium and mercury are a few exceptions.
16. Which Freshly cut metals have a bright metallic lustre? Freshly cut sodium metal metals have a bright metallic lustre like.
17. Which metals are can be cut with a knife? Potassium and sodium are very soft and can we cut with a knife. 100
18. Which metal is liquid at room-temperature? Mercury is the only metal which is liquid at room-temperature.
19. What happens to
gallium and cesium at a temperature
around 30 degree Celsius? Gallium with melting point of 29.76 degree celsius and Cesium
with melting point of 28.5 degree celsius exist in liquid state at around 30 degree Celsius. 20. How much long wire can be made from one gram of gold?
A wire off about 2 km can be drawn from one gram of gold 21. Name a metal which is non-malleable and brittle.
Zinc is a non-malleable and brittle metal. 22. Give some example of non-malleable and not ductile metals? Metal such as sodium, potassium, mercury, gallium, arsenic,
antimony and bismuth are non-malleable and not ductile. 101
23. What is Corrosion?
The process of slow degradation of the metal due to the attack of the atmospheric gases and water on the metal surface is called corrosion.
24. Describe the process of corrosion? Give an example of corrosion. When metals are exposed to atmosphere for a long time, they lose
their metallic lustre and become dull. As soon as the metals are obtained from their ores, the reverse process starts. Nature tries to change them back into the form in which they occur. The gases present in the air and water attack the metals and their surfaces get tarnished due to formation of compounds such as metal oxide,
sulphides and carbonates. Almost all metals corrode to some extent and the highly reactive ones corrode to a maximum extent. The most
common example of corrosion is the rusting of iron.
102
25. Which metals do not corrode easily? Gold and Platinum being noble and un-reactive metals, are least affected by the atmosphere and, hence, do not corrode easily. 26. Under which condition silver gets corrosion?
Silver articles are normally unaffected by the atmosphere but if the atmosphere contains a small amount of hydrogen sulphide gas, its surface becomes black after sometime. 27. What happens when Copper utensils are exposed to moist air? Copper utensils when exposed to moist air containing carbon
dioxide (CO2) gas for a long duration lost their shining brown surface and acquired a dull green coating. 28. What is known as basic copper carbonate? Copper utensils when exposed to moist air containing carbon CO2 gas for a long duration acquired a dull green coating. This dull
green coating is a mixture of copper hydroxide and copper carbonate and is known as basic copper carbonate.
103
29. What is the chemical formula of copper hydroxide and copper
carbonate? The chemical formula ofCopper hydroxide Cu(OH)2 and
Copper carbonate CuCO3. 30. Write the chemical equation of formation of basic copper carbonate
2 Cu + CO2 +O2 + H2O Moist air
Cu(OH)2 + CuCO3. Green coating
31. What is Rust? iron articles, when exposed to moist air for a long period of time,
develop the reddish-brown powder coating. The radius brown powder, which is formed on the iron article, when they are exposed to moist air, is hydrated Iron (III) oxide and is called rust. 104
32. What is the chemical formula of hydrated Iron (III) oxide?
The chemical formula of hydrated Iron (III) oxide is Fe2O3.x H2O in this chemical formula x is a variable.
33. Write the chemical reaction that takes place during the rusting of iron The chemical reaction that takes place during the rusting of iron is
given below. 4 Fe + 3 O2
Iron
+
oxygen from air
2 x H2O
water from moisture
Fe2O3 . x H2O
Rust (Hydrated Iron III oxide)
34. How rust completely destroys the iron air? Rust, the reddish brown powdery material is soft and does not adhere
strongly to the surface of iron metal and can be scrapped off easily from the surface of iron, exposing it fresh inner surface to air and moisture. Consequently, rusting continuous and the rust formed on the surface extended throughout the body and completely destroys the iron article.
105
35. How rust is affecting country’s economy?
Every year a large amount of money is spent to replace iron and steel structures. Hence, rusting proves quite expensive for country’s economy.
36. What are the method of prevention of rusting? Rusting of iron can be prevented by avoiding direct contact of iron
articles with air and moisture, this can be done by using the following methods•Applying grease and oil on the exposed parts of the iron articles. •Painting the surface of iron articles. •Galvanizing the surface of iron articles, that is, by coating the surface of
iron with a layer of zinc metal. •Electroplating the surface of iron articles with metals which are not
attacked by atmospheric moisture. •By Alloying.
37. Give an example of Galvanizing the surface of iron articles. iron pipes are coated with zinc, that is, galvanized iron pipes to protect iron from rusting. 106
38. What for GI stands? galvanized iron pipe is called GI pipes.
39. Give an example of electroplating. For example the shining parts of bicycle are given a coating of chromium (Chrome plating) to protect from rusting.
40. How galvanization of iron articles are done? For this purpose, iron articles are dipped in molten zinc and then after being taken out of molten zinc, these articles are cooled.
41. What is alloy? Give an examples of alloy. Alloy is a homogeneous mixture of either two or more metals or a
metal with a non-metal. Iron, when mixed with some corrosionresistant metal forms alloy which become resistance to rusting. For example, stainless steel is an alloy of iron, nickel and
chromium.
107
42. Write a short note on the Iron Pillar of Qutub Minar in Delhi? The Iron Pillar of Qutub Minar in Delhi is considered to be a
wonder of Indian metallurgy. The pillar, made up of wrought iron (purest form of iron) around 400 BC, shows no rusting even
today. A thin film of magnetic oxide of iron Fe3O4 is formed on its surface by painting it with the mixture of different salt followed by heating and immediate cooling. This process has till
date prevented the rusting of the Iron Pillar. 43. What is the use of Stainless steel?
Stainless steel is an alloy of iron which is used for the manufacture of cooking utensils and knives. 44. What is the role of iron in our body?
In our body, iron is an essential part of haemoglobin present in blood.
108
45. What are the uses of iron? Iron are used for
•Iron is used to construct bridges, •railway tracks,
•ships, •automobiles and •buildings.
•making Electromagnet, •sinks.
•pipes, •tanks, •gas cylinders,
•agriculture and industrial machines and tools. •nails, •bolts, chains and wire gauzes. 109
46. What are the uses of copper ?
•Copper is used to make electrical wires and cables. •Copper coils are used in many electrical appliances. •It is also used to make water pipes,
•electrical pipes, •steam pipes for plumbing,
•heating and ventilation. •It is used to make heating utensils, •car radiators and
•calorimeters. •It also forms useful alloys.
47. What is the use of Lead Lead is used to manufacture electrodes for automobile batteries and is also used to shield the radiations 110
48. What are the uses of Aluminium ? •
Aluminium used to make
•
overhead power cables,
•
cooking utensils,
•
thermal insulators.
•
Aluminium foils are used to packing used as packing material.
•
Aluminium alloys are used to make the engine parts bodies of
aircraft and vehicles. 49. What are the uses of Zinc?
•
Zinc is used mainly for galvanization of the iron.
•
It is used in dry cells and to prepare useful alloy such as bronze,
•
brass and German Silver.
•
It also used in a wide range of chemicals used in consumer products, agriculture feed supplements and fertilizers. 111
50. What are the uses Nickel? Nickel is a component of stainless steel which provides
• durability, • strength and resistance to corrosion. • It is also used to form alloys.
51. What are the uses Magnesium? Magnesium is used to manufacture of light alloys and flares.
52. What are the uses Tin? • Tin is used for tin plating of steel containers. • It is also used to make tubes for packing of pharmaceutical
products and toothpaste.
112
53. What are the uses Sodium? •
Sodium is used to transfer heat from the centre of atomic
reactors two boilers. •
It is used to extract metals, and
•
manufacture alloys and
•
to make Sodium Street lamps.
54. What are the uses Mercury ?
•
Mercury is used as thermometric liquid and
•
to manufacturer alloys called amalgams.
•
Silver
•
Silver gold and Platinum are used to make Jewellery and plating items for decorative purpose
113
55. To study the electrical conductivity of metals describe an experiment with sketch.
To study the electrical and thermal conductivity of metals taken are - Iron, copper, zinc, aluminum, silver and magnesium.
To know whether the sample conducts electricity or not the apparatus are set up as shown in the figure.
Now
Inserting
each
sample one by one in the circuit
the
to
bulb
see
whether
glows.
if
it
glows, it indicates that sample is a conductor of
electricity. If it does not glow, the sample is non
conductor of electricity 114
56. To study the thermal conductivity of metals describe an experiment with sketch.
The sample metal wire is clamped a as shown in figure. Now one pin is fixed with help of wax at the free end of the metallic wire away from the clamp.
When
the
sample
wire is heated near
the clamp end of the wire, it is observed that the wax melts
and pins fall down indicating metal
is
that a
the good
conductor of heat. 115
57. What is Aqua regia? What is the other name of Aqua regia?
Aqua regia is a fresh prepared mixture of concentrated nitric acid and concentrated hydrochloric acid in the ratio 1 : 3 by volume. The mixture is highly corrosive and fuming liquid. Aqua
regia can dissolve all metals including the noble metals such as gold and Platinum, though its constituents acid alone cannot
resolve them. The other name of Aqua regia royal water. 58. Which reaction prove to be useful in determining the relative reactivities of the metals
Displacement reaction may prove to be useful in determining the relative reactivities of the metals.
59. Draw a table to show the reactivity of series of metal. the reactivity of series of metal is shown below.
116
60. What is activity or reactivity series? The arrangement of metals in order of decreasing reactivity is
called reactivity series of metals or activity series of metals. 61. Describe activity or reactivity series.
All metals differ from each other in chemical reactivity because some metals are more reactive than others. Therefore, all metals are not equally reactive. The most reactive metal is
listed high in the reactivity series, while the least reactive metal is listed low in the reactivity series. 62. How study of the comparative reactivates of metal can be
made? A study of the comparative reactivates of metal can be made
by their reactions with oxygen, water and acids in which hydrogen gas is the product in most of the cases. But all metals do not react with oxygen, water and acids. 117
63. Draw a reactivity series table Reactivity Series tableMetals
Relative reactivity of metals
Potassium
K
Sodium
Na
Calcium
Ca
Magnesium
Mg
Aluminium
Al
Zinc
Zn
Iron
Fe
Nickel
Ni
Tin
Sn
Lead
Pb
[Hydrogen]
[H]
Copper
Cu
Mercury
Hg
Silver
Ag
Platinum
Pt
Most Reactive
Decreasing Chemical Reactivity
118
64. What is observed when three pieces each of iron , aluminium and copper, wrapped each one of them in a west Muslin cloth loosely and place this set up in the open atmosphere for 4 to 5 days?
It is observed that the iron piece has developed a reddish brown powdery layer of rust, while no such layer has formed on the
aluminium and copper pieces. 65. Write a short note on Non metals Non
metals
are
those
elements
which
do
not
possess
the
characteristics of metals. There are only 22 non-metals. They include Hydrogen(H), Nitrogen (N), Oxygen (O), Chlorine (Cl), Bromine (Br),
Iodine (I), Sulphur (Na), Carbon (C) , Phosphorus (P) , noble gases and a few more. Of the 22 non-metals, 12 non-metals are in the gaseous
state, one is in the liquid state and the rest are in the solid state at room temperature. Nonmetals are soft , dull, light, brittle, nonmalleable,
non-ductile,
non-sonorous,
non-
conductors
or
poor
conductors of heat and electricity and have low tensile strength. 119
66. Show an experiment with sketch to study the conditions necessary for rusting of corrosion of iron.
Three test tubes are taken and label them as A, B and C and then clean iron nails are placed in each one of them.
In test
tube A, some water is poured and corked it. In test tube B, some boiled distilled water and 1 mL of vegetable oil is poured and corked it. The oil forms upper layer and prevent air from
dissolving in water. In test tube C some anhydrous calcium chloride are putted and corked it. Anhydrous calcium chloride
absorb moisture, if any, present in air contain in test tube C. these test tubes are then kept aside for 2 days and thereafter , each of these test tubes are observed. It is observed that the
Iron nails placed in taste you A have rusted while those in test tube B and C are unaffected.
120
67. Which are the sources of non metallic elements?
Non metallic elements are quite evident in nature. They are present in the earth’s crust, ocean and in the atmosphere. Generally non-metals are very reactive and occur mostly in the
combined state though some may be present in free state as well. Oxygen and nitrogen occur in the free state in air while they are
present in the combined form in earth’s crust.Sulphur can exist in both free state and combined state in the earth’s crust. Noble
gases such as Helium , neon, organ, krypton and xenon occur only in the free state. Silicon occurs only in the combined form.
121
68. Draw a table of occurrence of Non metals. Non-metal
occurrence
Hydrogen
Sun, stars, water (11 % by weight) coal, natural gas, clay, petroleum , plants and animals
Oxygen
Earth’s crust, (oxides, carbonates and silicates of metals),
atmosphere (21% by weight) and water
(89% by weight)
Nitrogen
Atmosphere (78% by weight) and minerals such as nitre (KNO3) and chile saltpetre (NaNo3)
Carbon
Diamond, graphite, coal (60 - 90% by weight), atmosphere (in the form of carbon dioxide) earth’s crust (metal, carbonates and fossil fuels) and
living matter Silicon
Sand, silica (SiO2) and silicates (quartz, clay, talc,
asbestos etc) 122
Non-metal Sulphur
occurrence Earth’s
crust,
sulphides) , hair,
rocks
(metal
sulphates
and
petroleum and natural gases
(in the form of hydrogen sulphide), onion and garlic.
Phosphorus Phosphorus in the earth’s crust (0.1% by weight) volcanic eruption , Bony tissues and teeth.
chlorine
Earth’s crust, (0.045% by weight of chloride). volcanic eruptions, sea water (2.6 % by weight of chloride) minerals such as rock salt (NaCl) and
sylvite (KCL), etc. 69 Name two allotropes of carbon. Diamond and graphite which are the allotropes of carbon are
also pure forms of carbon. 123
70. Which are the most abundant element? Oxygen is the most abundant element in the earth's crust (45.5
% by weight) while hydrogen is the most abundant element in the universe. Silicon is the second most abundant element in
the earth's crust. 71. Name the non metals which have lustrous surface. Graphite and Iodine are non metals, but have lustrous surface.
72. Give an example of brittleness of non-metals. when non-metals like sulphur are hammered or stretched they
break into pieces. 73. Name the non metal which is very hard ? Diamond (an allotrope of
carbon) is the hardest known
substance, but a non metal.
124
74. What are the physical properties of Non-metals?
•
Non-metals are either solid (such as carbon, sulphur, iodine
and
phosphorus) or gases (such as nitrogen, oxygen, chlorine and noble gases) at room temperature. Bromine is the only non metal which is liquid at room temperature. •
Non-metals unlike metals are soft. For example, phosphorus is soft and can be cut with a knife.
•
Non-metals have low tensile strength that is they are not strong and
break easily. •
Non-metals unlike metals are non lustrous and have a dull appearance
•
Non-metals are non malleable and non ductile. They are brittle solids. Non-metals are non-conductors or bad conductors of heat and
electricity. •
Non-metals are non-sonorous that is they do not make a ringing sound when stuck.
•
Non-metals are usually have low densities.
•
Non-metals generally have low melting and boiling points 125
75. Name the nonmetal which is good conductor of heat and electricity. Graphite (an allotrope of
carbon), a non-metal is a good
conductor of heat and electricity.
76. Name one non-metal which has high melting and boiling point. Graphite which is an allotrope of carbon, is a non metal, has high melting and boiling point. 77. What are the uses of Carbon? •Carbon is the main constituents of all nutrients needed for
growth and development of living organism. •It's also used to prepare gun powder, sugar, dry ice, urea, cold
drinks and pencil lead. •It's also used to used as a lubricant and pigment. •It is used in metallurgy to form alloys with iron and also
electrodes for dry cells and batteries. •Carbon in charcoal, coal and coke is widely used as fuel 126
78. What are the uses of Oxygen? •
Oxygen is the supporter of life on earth.
•
It is also supports the process of combustion.
•
It is used in iron and steel industry.
•
It is also used in medicine to treat respiratory diseases.
•
It is mixed with other gases to facilitate respiration in spacecraft, highly flying aircraft and submarines.
•
It also helps the mountaineers to climb the mountains without suffering from ‘altitude sickness’.
•
Liquid oxygen is used as a rocket fuel.
•
Oxygen gas is also used for the cutting and welding of metals.
127
79. What are the uses of Hydrogen? •Hydrogen is used to prepare-
•hydrochloric acid, •ammonia,
•methanol, •rocket fuel, •petrol,
•fertilizer, •glasses,
•cosmetics, •soaps, •lubricants,
•cleaners and vegetable ghee from vegetable oil. •It is also used in metallurgy and for welding purposes.
128
80. What are the uses of Nitrogen? •Nitrogen reduces the rate of combustion.
•it is also used to prepare nitric acid (HNO3), nitrous acid (HNO2). •Explosives,
•fertilizers and light bulbs. •Liquid nitrogen is used as a refrigerant to preserve biological
specimens. 81. What are the uses of Phosphorus? •Phosphorus is used to prepare steel,
•matchsticks, •insecticides, •pesticides,
•toothpaste and shampoos. •Phosphates are used as lubricant, fertilizers and also for water
treatment.
129
82. What are the uses of Silicon?
•Silicon and is used in transistor circuit, •solar cells and computers (silicon chips). it is also used to make•lubricants, •medicines, •concrete bricks and glasses. 83. What are the uses of Sulphur?
•Sulphur is used to manufacture•paper pulp,
•fungicides, •fumigants,
•vulcanization of rubber, •rubber articles (such as tyres), •gunpowder, •sulfuric acid and as a bleaching agent. •Sulphur and phosphorus are used in making crackers. 130
84. What are the uses of Chlorine?
•Chlorine is used to •bleach wood pulp, •cotton and textile, It is also used to manufacture•dyes,
•drugs, •bleaching powder, •insecticides,
•medicines and plastic. •It's also used to sterilize drinking water.
85. What is the uses of Iodine (important) Iodine is used in making tincture of iodine, a commonly used antiseptic applied on cuts and wound.
131
86. How metals react with oxygen Most metals react with oxygen to form metal oxide which are
basic in nature. Metal + Oxygen
Metal oxide.
These basic oxides react with water to form bases (or Alkali)
which turn red litmus paper blue. However, different metals react with oxygen under different conditions because some
metals are more reactive than the other. 87. How magnesium reacts with oxygen? Magnesium on reaction with oxygen , burns with bright dazzling
light (a blinding white light) and forms a white powder of magnesium oxide. 2 Mg(s) Magnesium
+
O2(g) From air
2 MgO(s) Magnesium oxide (base) 132
88. How Sodium and potassium reacts with oxygen? Metals such as Sodium and potassium combine rapidly and so
vigorously with oxygen that many a time they catch fire. When exposed to air. To avoid explosion, they are kept in kerosene
oil. 4 Na (s) + O2 (g) Sodium
From air
Na2O(s) + H2O(l) Sodium oxide
Water
4 K (s) +
O2 (g)
potassium
from air
K2O
+
Potassium oxide (base)
2 Na2O (s) Sodium oxide (soluble in water) (base)
2 NaOH (aq) Sodium hydroxide (Alkali- base)
2 K2O (s) potassium oxide (soluble in water- base
H2O (l)
2 KOH (aq)
water
Potassium hydroxide (alkali) 133
89. How Copper and iron reacts with oxygen?
Copper and iron react with oxygen only upon heating to a very high temperature. 2 Cu (s) + O2 (g) Copper
from air
high temperature
2 CuO(s) copper II oxide black.
90. How metals like chromium and magnanese reacts with oxygen? •
Metals like chromium and magnanese form acidic oxides, such as, chromium trioxide and maganese (VII) oxide, in addition to the basic oxides.
91. How Silver and gold reacts with oxygen? Silver and gold resist combination with oxygen even at high
temperature.
134
92. How zinc, aluminium and tin reacts with oxygen?
Zinc , aluminium and tin form amphoteric oxides (oxides having both acidic and basic properties). 2 Zn (s) + Zinc
O2 (g)
2 ZnO (s)
oxygen
4 Al (s) + 3O2 (g) Aluminium Oxygen
Zinc oxide. 2 Al2 O3(s) Aluminium oxide.
93. How metals react with water ?
Metals react with water to form metal oxide or metal hydroxide with the evolution of hydrogen gas. Different metals react with water at different
temperatures. In case the reaction takes place at ordinary temperature, metal hydroxide is formed and if
the reaction occurs at a high
temperature, metal oxide is formed. Metal + water Metal oxide + water
Metal oxide + hydrogen Metal hydroxide
All metals do not react with water. The intensity of the reaction of different metals with water is different. 135
94. How sodium and potassium react with water ? Metals such as Sodium and potassium react quite violently
with water at ordinary temperature. In the case of potassium, reaction with water is so vigorous that the hydrogen gas evolved catches fire.
2 Na (s) + 2 H2O (l) Sodium
2 K (s) + Potassium
Water
2 NaOH (aq) + H2(g) Sodium hydroxide
Hydrogen
2H2O (l)
2 KOH (aq) +
Water
Potassium Hydroxide
H2(g)
Hydrogen
95. How zinc react with water ? Zinc reacts only with steam to form zinc oxide with evolution
of hydrogen gas. Zn (s) + Zinc
H2O(g) Steam
ZnO(s) + Zinc oxide
H2 (g) Hydrogen 136
96. How calcium react with water ? Calcium reacts with cold water at room temperature less
vigorously. Ca (s) + 2 H2O(l) Calcium
Water
Ca (OH)2 (aq) + H2 (g) Calcium hydroxide
Hydrogen
The heat evolved is not sufficient for hydrogen gas to catch fire. Calcium starts floating in water because the bubbles of hydrogen gas formed stick to the surface of calcium and help it float.
97. How Aluminium react with water? Aluminium also forms an oxide on reaction with steam but the
oxide formed makes a protective layer called corundum over the metal surface and thereby prevents further reaction. 2Al(s) + 3 H2O(g) Aluminium
Water
Al2O3(s) + 3 H2 (g)
Ammonium oxide
Hydrogen 137
98. How magnesium react with water?
Magnesium reacts with steam at high temperature to form magnesium oxide with the evolution of hydrogen gas.
Mg (s) + H2O(g)
Magnesium
Steam
MgO(s)
Magnesium oxide
+
H2(g)
Hydrogen
Magnesium reacts after a minute and starts floating due to the
bubbles of hydrogen gas sticking to its surface. But magnesium reacts slowly with hot water at ordinary temperature to form
magnesium Hydroxide with the evolution of hydrogen gas. Mg(s) + 2 H2O(l) Magnesium
Hot water
99. How iron react with water
Mg(OH)2(aq) + H2(g) Magnesium Hydroxide
Hydrogen.
Iron when heated strongly reacts with steam to form iron oxide
with the evolution of hydrogen gas. 3 Fe(s) + 4 H2O(g)
Fe3O4 (s)
Iron
iron oxide
Steam
+ 4 H2(g) Hydrogen
138
100. How Copper, Gold , Silver, lead and Platinum are react with water?
Copper ,
Gold , Silver , lead and Platinum do not react with
water or steam.
101. How metals react with Dilute Acids Metal reacts with dilute acids, such as , hydrochloric acid and sulfuric acid to form their respective salts with the evolution of
hydrogen gas. The metal displaces hydrogen atoms of the acid to form salt.
Metal + Dilute Acid 2 Na (s) + Sodium
Mg(s) + Magnesium
2 HCl (aq) Hydrochloric acid
2 HCl(aq) Hydrochloric acid
Metal salt + Hydrogen 2 NaCl (aq) + Sodium chloride
H2 (g) Hydrogen
MgCl2 (aq) + H2 (g) Magnesium chloride
Hydrogen 139
Mg(s) + Magnesium
Zn (s) + Zinc
Ca (s) + Calcium
2Al (s) +
H2SO4(aq)
Magnesium Sulphate
Sulfuric acid
2 HCl (aq)
ZnCl2(aq)
Hydrochloric Acid
2 HCl (aq) Hydrochloric acid
6 HCl(aq)
2 Fe (s) +
2 HCl (aq)
Iron
Hydrochloric acid
Cu (s) +
HCl (aq)
+ H2(g)
CaCl2(aq) + H2(g) Calcium chloride
Fast reaction
Hydrochloric acid
Hydrogen
Zinc chloride Hydrogen Violent Reaction
Aluminium
copper
MgSO4(aq) + H2(g)
Hydrogen
2 AlCl3(aq) + 3 H2 (g) Aluminium chloride
Fast reaction
FeCl2(aq) + Ferrous Chloride
Hydrogen
H2 (g) Hydrogen
No reaction
Hydrochloric acid 140
102. How metals like Sodium , Potassium and Calcium react with Dilute Acids?
Metals like Sodium , Potassium and Calcium react with dilute acids vigorously, whereas metals like magnesium, aluminium
and Zinc do not react vigorously. 103. How metals react with nitric acid ? Hydrogen gas is not evolved when a metal reacts with nitric
acid because nitric acid is a strong oxidizing agent. Nitric acid oxides hydrogen to water and itself gets
reduced to
oxides of Nitrogen such as N2O, NO and NO2.
141
104. Show an activity to compare reactivities of different
metals with a dilute acid. Three 250 ml beakers taken and numbered them as 1, 2 and 3. Poured 100 ml of dilute hydrochloric acid (HCl) in each of the
three beaker and put one rod one zinc rod in the beaker numbered 1, one iron rod in the beaker numbered 2 and the one
copper rod in the beaker numbered 3. It is observed that zinc liberates hydrogen gas very briskly, Iron liberates hydrogen gas slowly, while copper does not liberate hydrogen gas at all. This
shows that zinc is the most reactive metal among the three, copper is the least reactive metal, while the reactivity of iron
is intermediate between zinc and copper.
142
105. How metals React with bases? Metals react with Sodium Hydroxide to evolve hydrogen gas. Magnesium metal does not react with dilute aqueous alkali,
also called water soluble bases. Aluminium metal dissolved in sodium hydroxide to form the
Aluminates of the type [Al(OH4)]
-
along with the evolution of
hydrogen gas. 2 Al(s) + 2 NaOH (aq) + 6 H2O (l)
2 [Al(OH)4] – (aq) + 2 Na (aq) + 3 H2 The hydrogen gas, which evolves during the reaction, can be tested by bringing a burning splinter near the mouth of the
test tube in which the reaction is being carried out. The gas burns with a pop sound.
143
106. How the displacement of a metal by other metal is taken
place? A more reactive metal displaces a less reactive metal from its salt solution.
For example, if a piece of zinc metal is placed in copper sulphate solution (blue) in a beaker, it displaces copper from
copper sulphate solution and a colourless solution is obtained. Zn (s) + CuSO4 (aq) Zinc
Copper Sulphate (blue)
ZnSO4 (aq)
Zinc sulphate (Colourless)
+
Cu (s)
Copper (Reddish brown)
But when a piece of copper metal is placed in a solution of zinc
sulphate, no reaction takes place. This indicates that zinc is more reactive than copper.
Cu(s)
Copper (Reddish brown)
+
ZnSO4 (aq)
Zinc sulphate (Colourless)
No reaction
144
107. Write few examples of metal displacement reactions. Mg(s)
+
Magnesium
CuSO4(aq) Copper sulphate (blue)
Fe(s) + CuSO4(aq) Iron
Copper sulphate blue
Cu(s) + 2 AgNO3(aq) Copper
MgSO4(aq) +
Silver nitrate (colourless)
Zn(s) +
FeSO4(aq)
Zinc
Iron sulphate (Pale green)
Magnesium sulphate (colourless)
FeSO4(aq) + Iron sulphate (pale green)
Cu(s)
Copper (Reddish Brown)
Cu(s) Copper (Reddish Brown)
Cu(NO3)2(aq) + 2 Ag(s) Copper nitrate (blue)
ZnSO4(aq) + Zinc sulphate (Colourless)
Silver (Shining grey )
Fe(s) Iron
145
108. Show an activity to study the displacement reaction 10 ml of aqueous copper sulphate solution (blue) is taken in a test tube.
Put a clean iron nail in the test tube. Keep the test tube in a test tube stand undisturbed for half an hour. It is that the colour of the copper
sulphate solution changes from blue to pale green because of the formation of ferrous sulphate, which is pale green in colour. Reddish brown deposit of copper is formed on the surface of the iron nail. If the activity is performed
in the reverse manner, that is put a clean copper wire
in
the
ferrous
sulphate
(Pale green), no reaction takes place. This shows that iron is more reactive than copper or in other words,
copper
is
less
reactive than iron 146
109. How non-metals react with oxygen? Non-metals react with oxygen to form either acidic or neutral oxides. The acidic oxides of the non-metals such as carbon, sulphur and phosphorus dissolve in water to form acids which turn blue litmus paper red .
110. How Carbon react with oxygen? It reacts with excess of oxygen to form carbon dioxide, which is an acidic
oxide. C(s) + Carbon
O2(g) Oxygen (sufficient supply)
CO2(g) Carbon dioxide
Carbon dioxide dissolves in water to form carbonic acid CO2(g) + Carbon dioxide However,
H2O(l) Water
H2CO3(aq)
Carbon monoxide
carbon reacts with insufficient amount of oxygen to form
carbon monoxide, which is a neutral oxide and does not dissolve in water. C (s) + ½ O2(g) Carbon oxygen (insufficient supply)
CO(g) Carbonic acid 147
111. How sulphur react with oxygen?
Sulphur reacts with oxygen to form sulphur dioxide which is an acidic oxide. S (s)
+
O2(g)
Sulphur
SO2(g) sulphur dioxide
Oxygen
Sulphur Dioxide dissolves in water to form sulphurous acid.
SO2(g) +
H2O(l)
Sulphur Dioxide
Water
H2SO3(aq)
Sulphurous acid
112. How Phosphorus react with oxygen? It reacts with oxygen to form Phosphorus pentoxide, which is an acidic oxide.
4 P (s) + Phosphorus
5 O2(g)
2 P2O5 (s)
Oxygen
Phosphorus pentoxide.
Phosphorus pentoxide dissolves in water to form phosphoric acid.
P2O5(s)
+
Phosphorus pentoxide
3H2O(l) Water
2 H3PO4(aq) Phosphoric acid 148
113. How Hydrogen react with oxygen? Hydrogen reacts with oxygen to form water, which is a neutral
oxide. 2 H2(g) Hydrogen
+
O2(g) Oxygen
2H2O(l) Water
114. Name some neutral oxides. Besides water (H2O), oxide such as nitrous oxide (N2O)also
known as laughing gas and carbon monoxide (CO) , so are also neutral oxides. Their aqeous solutions are neither acidic nor basic. They also do not have any effect on red and blue litmus
papers 115. How non-metals react with water Non-metals are unlike metals, do not react with water. Due to
this property , highly reactive non-metals are stored in water, like phosphorus which catches fire spontaneously in air. 149
116. How nonmetals React with acids ? Non-metals unlike metals, do not displace hydrogen from acids.
Hence non-metals do not react with dilute acids. 117. How non-metals react with bases? The reaction of non-metals with base is quite complex. Some nonmetals react with alkalis (water soluble bases).Chlorine reacts with sodium hydroxide(NaOH) to form compounds which are used
to for bleaching purposes. Cl2 +
2 NaOH
Chlorine
Sodium Hydroxide
NaOCl + Sodium hypochlorite
NaCl
+
Sodium Chloride
H2O water
White Phosphorus ( P4) reacts with aqueous sodium hydroxide (NaOH) solution to form sodium hypophosphite and phosphine gas. P4
+
White Phosphorus
3 NaOH Sodium Hydroxide
+
3H2O Water
3 NaH2PO2 +
PH3
Sodium Phosphine hypophosphite 150
118. Write a short note on wood as non-metal. wood is made of carbon which is non metal. Wood is not ductile,
cannot be drawn into wires, it is a poor conductor of heat and electricity.
119. Which material of the inside the pencil is made of? The black material present inside the pencil is called lead. It is made up of graphite, a non-metal. The writing part of lead pencil
is a mixture of graphite, wax and clay, enclosed in a wooden case. 120. Are Copper and Aluminium rusted?
Copper and Aluminium are not affected by air and moisture and hence unlike iron. do not rust.
151
Back to contents
152
1.What is meant by endothermic reaction?
Chemical changes are results of chemical reactions. Some of these chemical reactions occur due to the absorption of energy and are said endothermic reactions as heat flows in.
2. What is meant by exothermic reaction? There are some chemical reactions that occur due to the
release of energy and are said to be exothermic reaction reactions, as heat flows out. 3. Define combustion.
The process of burning of fuel by oxidation in the presence of oxygen
(present
in
the
air)
is
called
combustion.
It
is
accompanied by release of energy (exothermic process).
4. Write the chemical reaction taken place during burning ? Fuel + Oxygen
Carbon dioxide + Water + Energy 153
5. Do one experiment to show energy change in the melting and burning of wax. Write your observations and conclusion. Experiment-
Requirement- a china dish, wire gauge, tripod stand, tongs and candles.
ProcedureCut some pieces of wax from a candle and put them in the china dish. Place the china dish on the wire gauge kept in the tripod
stand. Light another candle below the china dish. Observation- Burning of solid wax of the candle which is lighted
below the china dish is converted into new gaseous products, accompanied by the release of heat energy, as a result of chemical change. ConclusionThe wax in the china does absorb the heat and melts. This is a
physical change. 154
6.Give two examples of combustion.
(i) when magnesium ribbon is burnt in air, it burns with a white glow so as to form a white powder of magnesium oxide (MgO). (ii) A piece of charcoal or coal when burnt in the presence of
oxygen, evolve carbon dioxide gas along with heat and light. 7. Write the conditions for combustion.
The following three conditions are necessary for combustion. i.Presence of combustible substance - a substances that burns.
ii. Presence of Oxygen in Adequate Amount - a supporter of conversion.
iii. Attainment
of
Ignition
Temperature
-
the
minimum
temperature to which the combustible substance, a fuel, has to be heated such that it starts burning. 155
8. What is combustible substance? Give some examples. Combustible substances are those substances which can catch
fire easily. For example, clothes, paper, wood, fuel (such as LPG, CNG, Kerosene, petrol and diesel), etc.
A combustible substance will only burn and not support the process of burning. For example, hydrogen is combustible but does not support combustion. A combustible substance can
also be called a fuel. 9. What is the role of Combustible substances in combustion? A fire cannot be started if combustible substances are absent
156
10. What is the role of oxygen in combustion? How does insufficient supply of oxygen affects combustion?
For the process of conversion to take place, the presence of air is a must. A substance can only burn in the presence of oxygen. Hence, oxygen is also called the supporter of combustion. If the supply of
oxygen is insufficient, the burning process is not completed and it is called incomplete combustion.
Due to incomplete combustion,
lesser amount of heat and light are produced. For example, coal burns completely in sufficient supply of oxygen to form carbon dioxide gas but if the supply of air is less, then a poisonous gas called carbon monoxide is evolved. C
+
Coal
C Coal
O2
Sufficient of supply of air
+
½ O2
Insufficient of supply of air
CO2 +
Heat
Carbon dioxide
CO
+
Carbon monoxide
Heat 157
11.Explain why sleeping in a close room with a burning coal fire can be suffocating.
If charcoal or coal is burnt in closed room, then it undergoes incomplete combustion to produce carbon monoxide, which is a
poisonous gas. Hence, sleeping in a close room with burning charcoal or coal fire can be suffocating. This can lead unconsciousness and even death.
12. With a experiment show that air is essential for burning. Fix a burning candle on tumbler , cover the burning candle with
a glass jar. It is observed that the flame of the burning candle flickers, produces smoke and ultimately gets extinguished. This indicates that the presence of air is necessary for the process
of burning.
158
13. Why air has to blown in chulhas around wood or coal?
For chulas air has to blown around wood or coal. This provides oxygen for the wood or coal to burn easily.
14. What a blue flame indicates? A fuel burns completely in sufficient supply of oxygen and releases energy. A blue flame seen in the burning gas or
kerosene in stoves indicates complete combustion. 15. What a yellow flame indicates? Incomplete combustion takes place when the supply of oxygen is not sufficient. It leads to yellow or smoky flame. Black layers are formed on the surface (bottom of utensil or containers) in
contact with the yellow or smoky flame.
159
16. Respiration is basically in combustion reaction. Explain. Respiration is a process of breathing and using oxygen for various biological reactions that provide the energy required by the living
organism. This energy is released by the breakdown of complex food molecules into simpler molecules in the presence of oxygen
inhaled
during
breathing.
Thus.
respiration
is
basically
in
combustion reaction.
Enzymes of our body Food + Oxygen Carbon dioxide + water +Energy inhaled 17. Define Ignition Temperature
It is the minimum temperature to which the combustible substance, a fuel, has to be heated such that it starts burning.
160
18. What do you mean by kindling temperature? Ignition Temperature is also known as kindling temperature or ignition point.
19. What will happen to white phosphorus which is kept in a room and the ordinary room temperature rise to about 35C?
Ignition temperature of white phosphorus (P4) is 35C. If the ordinary
room
temperature
rise
to
about
35C
the
white
phosphorus (P4) will get spontaneously ignited.
20. Explain why a matchstick is lighted by striking the match along with a roughened surface.
The matchstick has red phosphorus along with other chemicals. On striking, friction is created. This generates enough hit to light the matchstick or make the chemicals catch fire. The wood used
in a match is also a particular variety whose ignition temperature is as much as the heat produced by the lighted matchstick head. 161
21. When water is boiled in a paper cup it does not catch fire, why? Explain with the help of an activity.
RequirementsTwo paper cups, a candle, a matchbox and water.
ProcedureIn one paper cup pour water while keep the other as it is. Light the candle. Move the candle near the two paper cups one by one.
Observations The empty paper cup catches fire while the other paper cup becomes hot and if heating is continued water starts boiling.
Conclusion – This is due to the fact that the heat supplied to the paper cup is
transferred to the water by conduction. The water present in the paper cup keeps the temperature of the paper cup below its ignition temperature and hence , the paper cup does catch fire. 162
22. Explain the ignition of piece of paper by a match stick. when we want to ignite a piece of paper, the burning matchstick supplies heat to raise the temperature of the paper to its ignition
point (which is 233C). At this temperature, the paper will catch fire and burn.
23. In order to initiate a wood/coal fire, a simple burning matchstick will not work. Why? We have to dip a piece of cloth in kerosene and then burn the
cloth. This burning cloth when placed under a heap of wood/ coal, initiates a wood/ coal fire.
This is because the ignition
temperature of wood/coal is quite high and cannot be attained
using a lighted matchstick. On the other hand the ignition temperature of the kerosene is quite low due to which it catches
fire very quickly.
163
24. Why special care is needed to store kerosene?
The ignition temperature of the kerosene is quite low due to which it catches fire very quickly. Hence, special care is needed to store kerosene. 25. Are the ignition temperature of different substances same? The ignition temperature of different substances is different and
they catch fire at different temperatures. Some substances have low ignition temperature, other substances have moderate and still
others have high ignition temperature. 26. Some substances which catch fire only on strong heating, why? Give some examples of such substances.
Some of the substances having high ignition temperature are coal, coke, charcoal, wood. They catch fire only on strong heating.
27. What does fire control consists of ? Fire control consists of depriving of fire of fuel, oxygen or heat to prevent it from spreading or for putting it off entirely. 164
28. What do you understand by inflammable substances? Give
some examples of inflammable substances. The substances whose ignition temperature is extremely low and
which
can
catch
fire
easily
are
called
inflammable
substances. For example, white phosphorus, petrol (gasoline), Kerosine, Liquefied Petroleum Gas (LPG), Compressed Natural
Gas (CNG), Alcohol etc. Dry grass, dry wool and paper are some other examples. 29. Why care should be taken while storing and transporting
these inflatable substances. The
ignition
temperature
of
inflammable
substances
is
extremely low and can catch fire easily. Hence, care should be taken while storing and transporting these inflatable substances.
165
30. What are the three most important requirements to initiate a fire ?
The three most important requirements to initiate a fire are •
Fuel (combustible substance)
•
Air (to produce oxygen which is a supporter of combustion)
•
Heat (to increase the temperature of the fuel overcome its ignition temperature)
31. Why fire brigade pours water on the burning fuel in order to extinguishing the fire? Water is used to extinguish ordinary fires because it reduces
the temperature of the substance (that has caught fire) below the ignition temperature. Moreover, water vapour thus formed
surrounds the burning substance thereby cutting off the oxygen supply. 166
32. Why when oil catches fire, pouring of water will not help ? When oil catches fire, pouring of water will not help because
the ignition temperature of oil is low. Also, oil floats on water as oil and water do not mix with each other. Hence, water actually ends up in spreading the fire.
33. Why carbon dioxide is used in fire extinguisher ? Carbon dioxide being heavier than oxygen, acts as a blanket
and cover the fire thereby cutting off the oxygen supply.Carbon dioxide is the best extinguisher to douse the fire produced by burning of inflammable substances (such as LPG and petrol) as
well as those involving electrical appliances. Carbon dioxide does not destroy the electrical equipment while extinguish the fire.
167
34. How sand helps in extinguishing small fires? Small fires can be extinguished by throwing sand over it. For
example, when sand is thrown over the burning oil, the sand covers it like a blanket, cutting of air supply to the burning oil and the fire gets extinguished.
35. Explain the construction and working of fire Extinguisher. fire extinguishers are consists of a handled cylindrical pressure
vessels (generally of red colured cylinder) containing an agent which can be discharged to extinguished fire Most of the fire extinguishers work on either of the following
principles. •
reducing the ignition temperature of the substance that has caught fire.
•
cutting off supply of oxygen. 168
36. Where usually fire extinguishers are used? What type of fires are extinguished by a fire extinguisher? extinguishers are usually suspended on the wall in offices,
trains, malls and many other public places. A fire extinguisher is used to extinguish or control small fires by directing onto the flame a substance that cools the building material and deprived
the flame of oxygen. 37. Explain the working of soda-acid fire extinguisher.
In a soda-acid fire extinguisher, water is expelled out at a high pressure by the generation of carbon dioxide gas. The carbon dioxide (CO2) gas is produced as a result of mixing
of sodium hydrogen carbonate (NaHCO3) with sulfuric acid (H2SO4), when the extinguisher is tilted.
NaHCO3 + Sodium hydrogen carbonate
H2SO4 Sulfuric acid
Na2SO4 + Sodium sulphate
2H2O + 2 CO2 Water
Carbon dioxide
169
38. Who invented the first automatic fire extinguisher and when? The first automatic fire extinguisher was invented in England in
1723 by chemist called Ambrose Godfrey. 39. Who invented the modern-day fire extinguisher and when? Describe its construction.
The modern-day fire extinguisher was invented by British Captain, George William Manby in 1818. It consisted of a copper vessel having three gallons of potassium carbonate (pearl ash)
solution contained with the compressed air. 40. Explain the term “Flame”?
Flames are associated with the fires or combustion. Flame is basically a region where burning or conversion of fuel takes place to produce heat and light
170
41. Are all burning substances produce flame? Explain your answer with example.
All substances which burnt do not produce the flame. Only those substances which vaporize or burning produce a flame. For example charcoal (or coal) does not vaporize and so does not produce a flame. It simply glows on the other hand, a candle, when burnt gives light in the form of a flame.
42. With the help of an activity show that the substance that vaporize when heating burn with the flame? Procedure Hold certain pieces of camphor, charcoal and wood in a candle flame, with the help of tongs, one by one
Observation. It is observed that camphor burns with a flame, charcoal does not burn with a flame but glow and wood first burns with the flame but after sometimes simply grows like charcoal. 171
43. Why candle burn like a flame?
When the wick of the candle is lighted, solid wax melts and rises up through the wick. The heat from the flame of the matchstick vaporizers the wax and the vapours of the wax so
formed react with the oxygen to burn like a flame. The vapours stay longer in the hot regions of the flame and start burning completely in the presence of oxygen.
44. On which factors the colour of the flame depends? the colour of the flame depends on the following three factors
•
Nature of combustible substance,
•
Temperature, and
•
Availability of oxygen or air.
172
45. Write the full form of NASA. What is its discovery about flame formation ?
National Aeronautics and Space Administration (NASA) NASA discovered that gravity also plays an important role in
flame formation and composition. In microgravity or zero gravity, such as an outer space environment, the
flames become
spherical, with a tendency to become bluer and more efficient. In
zero gravity, the hot combustion products are not carried away from the fuel sources resulting in a spherical flame front.
173
46. What are the types of flames? Explain them.
A flame can be of the following two types Luminous Flame A flame which is accompanied by heat and light is called
luminous flame. It is a yellow in colour. This flame is produced by if the burning of the substance takes place in inadequate supply of oxygen leading to incomplete combustion. The yellow
colour of the flame is due to the glow of hot un-burnt carbon particles
produced
due
to
incomplete
burning.
The
tempererature of this flame is lower and it leaves behind unwanted residues and black soot. Like a candle, mustard oil and kerosene oil also produced yellow luminous frame.
174
Non-Luminous Flame A flame which is accompanied by heat but very less amount of light is a non-luminous flame. It is blue in colour. This flame is
produced if the burning of a substance takes place in the presence of adequate amount of oxygen. The temperature of this flame is quite high and it does not leave behind any residue.
Hence, the blue flame is clean. Examples or flames of the Bunsen burner and the flame of LPG gas stove their design in
such that it provides enough oxygen for complete combustion.
175
47. What are the zones of a candle flame? Explain it with the help of a diagram. A candle flame can be divided into three zones on the basis of
the different reactions taking place in the different parts of the candle flame which, in turn, depends on the amount of air received by various regions of the flame (draw figure 5.12 of
your text book). Innermost or Non-Luminous Zone
In this zone, contains un-burnt wax vapours. It appears dark black due to lack of oxygen. It is a region of no combustion. It is the least hot region of the candle.
176
Middle or Luminous Zone In this zone, the wax vapours start burning. The flame appears
yellow because the vapours are partially burnt. It is the most visible part of the flame. The oxygen available in this region is not sufficient for the wax vapours to burn completely. This is the opaque and luminous zone of the flame. Carbon particles are present in the zone. These carbon particles glow at high
temperature (590C), emit light and impart yellow colour to the zone. The temperature of the zone is not very high in comparison to outer zones of the candle flame.
Outer or Invisible Zone It is the hottest zone of the candle flame. This part of the flame
is invisible. In the zone, the combustion is complete because the oxygen supply is plentiful. The wax vapours burn completely to form water and carbon dioxide. The flames appears blue. 177
48. Why goldsmiths blow the outermost zone of a flame with a blowpipe to melt metals such as gold and silver?
The outermost zone of a flame It is the hottest zone of the candle flame. Hence, goldsmiths blow the outermost zone of a flame with a blowpipe to melt such as gold and silver. 49. Why a black deposit is formed If a piece of carbon board is held a few inches above a burning candle ?
Some carbon particles in the luminous zone do not burn at all and move out with gases. There are others that do not burn completely and form carbon monoxide gas. If a piece of carbon
board is held a few inches above a burning candle, a black deposit, which is a simple collection of
unburnt carbon
particles is formed. It is called soot.
178
50. What is candle Fish , where it is found? Candle fish, also called eulachon or oulachon or smelt, are fish
which are full of oil. When they are dried, placed upright and lit, they burn from end to end like a candle. Candle fish is a
peculiar to the specific coast of the United States. 51. What are fuels? The chemical substances which on burning in oxygen, produces
energy in the form of heat and light are known as fuels. 52. How fuels releases energy? Fuels releases energy either through chemical reactions such
as combustion or through nuclear reactions. 53. From where we obtain fuels?
Fuels are obtained from earth’s crust. They mainly contain carbon and hydrogen and sometimes small amount of sulphur or minerals. 179
54. What is an important property of a fuel?
An important property of a fuel is that its stored energy can be released when needed. The release of stored energy is controlled in such a way that energy can be harnessed to produce work.
55. What are the types of fuels on the basis of occurrence ? On the basis of occurrence fuels can be divided into the following
categories: Natural Fuels or Primary Fuels These fuels occurred naturally and are available in the direct.
These can be burnt as such to release the heat energy. example,
coal,
natural
gas,
petroleum,
wood,
cattle
For dung,
agriculture waste etc. Processed Fuels or Secondary Fuels These fuels are derived from the primary fuels by various physical
or chemical processes. For example, kerosene, diesel, charcoal, petrol, coal gas, coke , LPG, water gas (CO + H2) etc.
180
56. On the basis of their physical states, what are the various
subgroups of fuels ? Various groups on fuels on the basis of their physical states: Solid Fuels
These
are
the
temperature.
fuels
For
which
example,
exist coal,
in
solid
coke,
state
charcoal,
at
room
firewood,
agriculture wastes etc.
Liquid Fuels These
are
the
fuels
which
exist
in
liquid
state
at
room
temperature. For example, petrol, gasoline, kerosene, diesel, alcohol (ethanol), etc. Gaseous Fuels
These are the fuels which exist in gaseous state at room temperature. For example, methane, ethane biogas, petroleum
gas, natural gas, etc 181
57. What are characteristics on an Ideal Fuel?
An ideal fuel has the following characteristics: •
High calorific value,
•
burns easily at a moderate rate
•
has a moderate ignition temperature,
•
Does not produce pollutants,
•
Is cheap, readily available, can be stored and transported easily.
58. Define Calorific value or Heating value of the fuel. What is its
unit ? Calorific value or Heating value of the fuel is defined as the amount of heat evolved in kilojoules when one kilogram of the
fuel is burnt completely to form carbon dioxide gas and water. The units of calorific value of a fuel is KJ/Kg. 182
59. What are the criteria for choosing a fuel for application? Following are the criteria for choosing a fuel for application-
•Physical state of the fuel; •Calorific value; •Ignition temperature of the fuel; •Moderate rate of combustion of the fuel; •Low Content of Non-combustible Materials in the fuel;
•Easy Availability and Cost effectiveness of the Fuel; •Proper storage and transport of the fuel; •Residue from the Fuel;
•Emissions from the fuel; •Apt usability of fuels.
183
60. Why liquid fuels are most advantageous? Solid fuels are difficult to use but easy to store. Gaseous fuels
are easy to use but difficult to stores. They have to be compressed to a high pressure and then stored in a cylinder or tankers. They may be dangerous in case there is a leak, as the fuels sprayed very first. Liquid fuels are most advantageous, as they can be stored and used easily.
61. Why some fuels have low calorific value? What should be the calorific value of a fuel? Fuels containing oxygen in them have low calorific value. The
higher the calorific value of a fuel better the fuel is. A fuel which gives more calories put unit weight and would be an
ideal fuel.
184
62. What should be the Ignition temperature of a fuel?
A good fuel is one which is moderate ignition temperature (neither very high nor very low). Ignition temperature slightly higher than the room temperature is taken as satisfactory.
63. How should be the rate of combustion of a fuel? The rate of combustion of the fuels should be such that the heat released in a controlled manner. This ensures that fire neither
dies nor explodes. The fuel should burn smoothly and not sputter. Thus, the rate of oxidation reaction of a fuel should be
moderate. 64.Why
fuel
should
have
low
content of
non-combustible
materials in the fuel?
An ideal fuel should have quite low content of non combustible material. The non-combustible materials present in fuel give out
undesirable harmful gases which may cause air pollution 185
65. Why safe disposal of residue of a fuel is not easy and it poses a
problem? Some fuel leaves behind considerable amount of harmful chemicals in the residue. The problem becomes complicated when very large
amount of fuel are burnt such as in thermal power plants, thousands of tons of ash (residue) is produced everyday from burning of coal.
66. What type of pollutants are emitted from the fuels which cause air pollution? The non-combustible materials present in fuel are its impurities. One
of the sources of air pollution is the emission from the burning of fuels. All fossil fuels emit carbon dioxide gas during burning.
Moreover,
it emits suspended particulate matter (SPM), sulphur
dioxide (SO2) or carbon monoxide (CO) gases. A fuel is considered to be better if it does not produce these pollutants. When the fuel is
heated, these impurities burn to give out undesirable harmful gases. 186
67. What do you mean from apt usability of fuels? The fuel should not be more useful for purposes other than its use
as a fuel. For example, coke, though a solid fuel, is preferred to be used as a reproducing agent in industrial applications. Also, wood is a fuel but its indiscriminate denudes the forest cover. The cutting of trees can also lead to environmental degradation which can result in natural calamities such as flood droughts,
etc. Hence, wood is not an ideal fuel. 68. Why a fuel having a very high ignition temperature or very low ignition temperature are advisable to use?
The fuel having a very high ignition temperature will have to heated very strongly before it catches fire. On the other hand, if
the ignition temperature of a fuel is very low, it is risky to handle as it may catch fire itself. Therefore, these type of fuels are not advisable to use. 187
69.Which fuel has highest Calorific value? Hydrogen has the highest calorific value among all the fuels.
70. What is Ignition temperature of a fuel? Ignition temperature is the minimum temperature at which the fuel catches fire.
71. How fuel causes air pollution? The non-combustible materials present in fuel are its impurities.
When the fuel is heated, these impurities burn to give out undesirable harmful gases which may cause air pollution. 72. Why large number of precautions have to be taken to handle,
store and transport of fuels. Fuels are basically extracted and purified in factories. They have to be transported to either houses for domestic use or to
industries for industrial use. Quite a Some of the fuels may be highly inflammable. 188
73. Write the calorific values of the followingCow dung cake, wood Coal , Petrol , Kerosene, Diesel , Methane,
CNG , LPG, Biogas, Hydrogen. FUEL COW DUNG CAKE
CALORIFIC VALUE IN KJ/KG 6000-8000
WOOD
17000-22000
COAL
25000-33000
PETROL
48000
KEROSENE
46200
DIESEL
44800
METHANE
50000
CNG
50000
LPG
55000
BIOGAS HYDROGEN
35000-40000 150000 189
74. An ideal fuel should be easily available in large quantities and should also be cheap. Explain.
Some fuels have all the characteristics of an ideal fuel such as high calorific value, moderate rate of combination and low contained of non combustible materials but these can be
expensive. For example, a car runs very efficiently on high octane petrol which is a fuel. But the cost of this fuel is very
high and is also not readily available at petrol filling stations. High octane petrol is therefore not widely used. Thus an ideal fuel should be easily available in large quantities and should
also be cheap 75. What is CNG? The full form of CNG is Compressed Natural Gas . CNG has high
calorific value or 50,000 KJ/Kg and contains methane as a major constituent. It is a clean fuel. 190
76. What are the advantages of CNG as a fuel? The advantages of using CNG as a fuel are given below: •
it leaves no residue after combustion
•
it does not emit sulphur dioxide(SO2) gas and any suspended particulate matter (SPM)
•
it has a high calorific value (though less than that of hydrogen)
•
It has a reasonable cost which makes a popular fuel.
77. Write the chemical reaction taken place during burning of CNG fuel.
CH4
+
2O2
Methane Oxygen
CO2 + Carbon dioxide
2H2O + heat energy water
191
78. What is the disadvantage of using CNG as a fuel?
The disadvantage of using CNG as a fuel is that it has low ignition temperature. The barrier in its wide usage is that it is available only where arrangements for its supply through pipes have been made.
79. What are the uses of CNG? CNG is being increasingly used as a fuel in automobiles, cars, buses
and trucks and also for generating electricity. It is also helps in reducing air pollution. 80. What is LPG? The full form of LPG is Liquefied Petroleum Gas. Petroleum gas is basically a mixture of three gaseous hydrocarbons, namely ethane
(C2H6), propane (C3H8) and butane (C4H10). But the main constituent of the petroleum gas is butane. Petroleum gas can be liquefied easily by
applying pressure. In the liquefied form, it is known as (Liquefied Petroleum Gas). It is supplied to consumers in iron cylinder. LPG changes back to gas when the pressure is released at the burner. 192
81. Why ethyl mercaptan is mixed with LPG? What is the chemical formula of ethyl mercaptan ?
LPG is a colorless, odorless and inflammable gas. It is difficult to detect its leakage from the cylinders. To detect is leakage from the cylinder, it is mixed with a small amount of ethyl
mercaptan having characteristics unpleasant or foul smell. The chemical formula of ethyl mercaptan is C2H5SH. Write the characteristics of LPG gas?
characteristics of LPG gas•
The calorific value of LPG is quite high (55000 kJ/kg).
•
It does not leave any residue on burning and the emissions are free from SPM (suspended particulate matter)
193
82. Write the chemical reactions taken place when LPG is burn
in atmosphere? Following reactions are taken place during burning of LPG-
2C2H6 +
7O2
Ethane Oxygen
C3H8 + Propane
5O2 Oxygen
2C4H10 + 13O2 Butane Oxygen
4CO2 + Carbon dioxide
3CO2 +
6H2O
+ heat energy
Water
Energy
4H2O +
Carbon dioxide
heat energy
Water
Energy
8CO2 + 10H2O + heat energy Carbon dioxide
Water
Energy
194
83. What is the disadvantages of LPG as a fuel? The only problem with its usage is that LPG has quite low ignition
temperature. However, the accidents are minimum when it is used as a fuel.
84. What is the advantages of LPG over CNG? The availability of LPG is more widespread than CNG as it is supplied in iron cylinders which are easily transportable. It is
more expensive than CNG but for domestic use, its prices of subsidized by the government.
85. What are the advantages and disadvantages of Kerosene? The calorific value of kerosene is moderate. It does not leave any residue on burning. Its ignition temperature is also above the
room temperature and it can be stored safely. Further, as it is a liquid, it can be transported easily. The emissions from kerosene contain carbon monoxide gas and soot which are very hamful. 195
86. Write the chemical equation taken place during burning of kerosene?
Kerosene +
Oxygen
Carbon +
Water +
dioxide
Heat energy
87. What are the advantages and disadvantages Petrol? Petrol is a good calorific value ( 48000 Kj/kg) but it is lower than that of LPG or CNG. It leaves no residue on combustion. It
is used as a fuel for cars, motorcycles and other vehicles. Being a liquid, it can be transported easily. But petrol is costly.
It is not easy to store petrol because of its low ignition temperature. 88. Write the chemical equation taken place during burning of
Patrol? Patrol +
Oxygen
Carbon + dioxide
Water +
Heat energy 196
89. What are the advantages and disadvantages of diesel
The calorific value of diesel is slightly less than that of petrol. Like
petrol,
it
leaves
no
residue
on
combustion.
The
disadvantages of using diesel as a fuel is that, very often, its
emission contain pollutants such as suspended particulate matter (SPM) and sulphur dioxide gas. It is easy to store as diesel
because of its ignition temperature is moderate. Being a liquid, it is easy to transport. Diesel is cheaper than petrol in India 90. Why has the Delhi government banned the running of buses
on diesel within the city? The emission from burning of diesel contains pollutants such as
suspended particulate matter (SPM) and sulphur dioxide gas. Because of this reason, the Delhi Government has banned the running of buses on diesel within the city. 197
91.Write the chemical equation taken place during burning of diesel?
Diesel + Oxygen
Carbon + Sulphur + Heat + SPM + Water dioxide
dioxide energy
92. Write uses of diesel as a fuel? It is used as fuel for cars, buses, locomotives, tractors, trucks and diesel generators.
93. What are the advantages and disadvantages of Coal It has a lowest calorific value. Coal primarily contains carbon. It
burns to form carbon dioxide gas, leaving behind ash as residue. Disposing of the residue is a big problem. The emission of suspended particulate matter (SPM) and sulphur
dioxide gas from burning coal causes high levels of pollution. It is easy to store as it is a solid.
198
94. Why coal is largely used as a fuel in thermal power plants and many industries.
The advantages of using coal as a fuel in lie in its low price and deposits in India. Therefore, coal is largely used as a fuel in thermal power plants and many industries.
95. Write the chemical equation taken place during burning of diesel? Coal + Oxygen
Carbon +
Sulphur +
Ash +
Heat
dioxide
dioxide (Residue) energy
96. What is LNG?
CNG is changed to liquid form by applying high pressure and low temperature by refrigeration. The liquid thus obtained is called LNG (Liquefied Natural Gas)
199
97. Write the advantages of Hydrogen as a fuel. Hydrogen has the following advantages of fuel: •it is the highest calorific value ( 150000 kJ/kg) among the
fuels. •it leaves no residue on burning.
•it does not produce any harmful emissions on burning. •the gases emitted on burning hydrogen consists only of water.
•The disadvantage of using hydrogen as a fuel is that it has low
ignition
temperature
(below
room
temperature).
Moreover, it is costlier also. •However, hydrogen is still considered to be the future fuel.
200
98. Which fuel is the best and why? The fuels you have read about have advantages and disadvantages. It is difficult to decide which fuel is the best. However, presently
Compressed Natural Gas (CNG) is considered to be a very good fuel. But it cannot be transported conveniently. Efforts are being made to
solve its transportation problem by changing it is liquid form, at high pressure and low temperature by refrigeration. 99. What are harmful by-products of combustion of fuels?
When
a
fuel
undergoes
oxidation
or
combustion
reaction,
it
produces carbon dioxide and water. In most of the fuels, other
reaction
products
are
also
emanated.
These
include
carbon
monoxide gas, sulphur dioxide gas, carbon or soot particles. The byproducts when mixed with air, change the quality of air which we
inhale. This results in many harmful effects on human beings and environment. 201
100. What is air pollution? The imbalance caused in the atmospheric proportion of gases
by burning of fuels is termed as air pollution. 101. What are the some undesirable by-products of burning ?
Why it is harmful? During burning of some fuels some carbon particles do not burn at all while others burn incompletely. As a result, some
undesirable by-products like soot and carbon monoxide gas are formed. Besides being undesirable, they're quite harmful as well. The carbon particles can cause respiratory diseases such
as asthma. 102. What are the pollution caused by Burning of Coal?
Coal contains oxygen, sulphur, hydrogen, carbon and nitrogen. When coal is burnt, carbon dioxide, carbon monoxide, sulphur dioxide and smoke (soot) are emitted. 202
103. What is greenhouse gas ?
Carbon dioxide (CO2) gas is formed when coal is burnt in sufficient supply of air. Carbon dioxide gas is a pollutant and excess of carbon dioxide gas traps sun’s heat energy thereby increasing the
atmospheric temperature. This leads to global warming. Carbon dioxide gas is also known as greenhouse gas as it causes
greenhouse effect. 104. Exaplain in detail what is the harmful effect Carbon monoxide (CO) gas?
Carbon monoxide (CO) gas is formed when coal is burnt in insufficient supply of oxygen. It is a poisonous gas and is harmful
to our bodies. When carbon monoxide is inhaled, it combines with haemoglobin of the blood in form of carboxyhaemoglobin (COHb) which lacks the ability to carry oxygen to the tissues. This leads to
suffocation due to inadequate supply of oxygen the blood. The excess levels of carbon monoxide can even cause death.
203
105. What is acid rain? Sulphur dioxide (SO2) gas is formed when coal is burnt. It is
very poisonous, suffocating and corrosive gas. It can mix with air and moisture (present in air) so as to form sulphuric acid.
Sulphuric acid can combine with rain to form acid rain which is highly corrosive and can damage marble buildings crops even harms human beings and animals. For example, the Taj
Mahal is turning
yellowish because of this type of pollution
caused by refinery that is in its close proximity.
Oxides of Nitrogen (NOx) released by automobile exhausts are formed by the oxidation of nitrogen present in the air at high temperature. These oxides are corrosive and poisonous (toxic)
in
nature
and,
therefore,
form
undesirable
and
harmful
products. They dissolve in rainwater thereby making it acidic.
204
106. How the pollution caused by burning petroleum based products ?
Diesel and petrol are the fuels used in motor vehicles. These petroleum products contain hydrocarbons along with lead chemicals. Lead chemicals are added to make these fuels heavy and avoid knocking in the vehicles. When these products
are
burnt,
they
emit
unburnt
particles,
some
alcohols, acids and lead compounds. The vehicular engines produce heat from petrol in a very short time. This results in incomplete burning of petrol. The vehicular engines release
un-burnt hydrocarbons, carbon particles, and carbon monoxide along with some acids and alcohols in the air. The lead
compound known as Tetraethyl lead Pb(C2H5)4 , which is added to petrol to slow down its rates of combustion, is also a major pollutant. 205
107. What is smoke?
Smoke is the carbon component which is not converted into either carbon dioxide or carbon monoxide. It is black in colour. Smoke
causes air pollution. It is harmful to inhale smoke, as it causes suffocation.
Black smoke blackens clothes, buildings monuments
etc.
108. What is soot? Soot is the suspended particulate material (SPM) and affects the
respiratory system. 109. Fill in the blanks(i) Almost every change in the universe involves either a …………
(
) or a ---------- (
) of energy.
Ans - gain (absorption), loss (release)
(ii) The change can either be ----------, such as the ---------------------- or ------------- such as ------------. Ans- Physical, melting of solid to liquid, chemical , burning of a fuel
206
Back to contents 207
1.What are the Conventional and non-conventional sources of Energy
208
2. What are the most commonly used fuels in our country? How their distribution is in rural and urban areas?
The most commonly used fuels are wood, coal and petroleum. In rural areas, about 80% of the domestic requirements are made by wood, coal and cow dung cakes. In urban areas,
petroleum and natural gas are the main sources of energy. 3. What are the non renewable sources of energy? Why non renewable sources of energy are to be use judiciously?
Coal, petroleum and natural gas are non renewable sources of energy as they cannot be easily replenished.
But the fact is
that they are being used up much faster than they can be made by natural processes. Hence, we must use this reserve judiciously to meet the future demand.
209
4. What is wood? In what ways wood fuel is important to us? Wood is a small material derived mainly from trees. It is
composed of cellulose. Wood fuel is the wood used as fuel. The burning of wood is
currently the largest used of energy derived from the solid fuel biomass. Wood fuel can also be used for cooking and heating purposes and occasionally for fuelling steam engines and steam
turbines that generate electricity.
Wood fuel may be available
as firewood, charcoal, chips and sawdust. The particular form
used depends upon the factors such as source, quantity and application. Wood maybe burnt in a furnace, stove, fireplace, in a campfire or used for bonfire. Wood is the most easily available
form of fuel.
210
5. What are the various forms in which wood fuel are available? Wood fuel may be available in the form of logs, bolts and blocks
6. Name the discovery which is regarded as the greatest achievement of humanity? The discovery of ‘fire’ is regarded as one of humanity’s most
important advances and greatest achievement of humanity. 7. What is termed as deforestation?
Forest are the key sources of wood. Since wood has an infinitely number
of
uses,
indiscriminately
cut.
trees
are
being
This
has
led
degradation of, trees are
to
indiscriminately continual
loss
is or
indiscriminately cut. This has led to
degradation for forest habitat, termed as deforestation.
211
8. Enumerate some consequences of deforestation. Human activities that destroy forests maybe lead to –
•
melting of ice caps,
•
change in the climatic conditions,
•
Changing the shape of the continuance,
•
greenhouse affects,
•
soil erosion,
•
reduction in water table and
•
Landslides.
9. Why the uses of wood fuel should be discouraged?
Though wood fuel is a source of energy, its use is being discouraged nowadays because the continuous cutting of trees for human needs is adversely damaging the biotic and abiotic
components of the environment. 212
10. What are fossil fuels? How and when they were formed? Give some examples of fossil fuel.
Fossil are the dead remains of plants and animals which were buried deep inside the earth millions of years ago. Fossil fuels are derived from fossils.
They have been formed by the decomposition of animal and plant remains buried in the earth’s crust million of years ago,
even before the age of dinosaurs. The examples of fossil fuel are - coal, petroleum and natural gas.
11. Why Fossil fuels should not be used indiscriminately? Fossil fuels are practically non renewable as they take a long period (million of years) to form and hence are limited to
quantity. Once used, this cannot be replenished and may exhaust soon if they are used indiscriminately. 213
12. What are the conventional and non-conventional sources of energy?
Conventional energy sources are: (a) Fossil fuel energy
(b) Hydraulic energy (c) Nuclear energy Non-Conventional Energy Sources Introduction
(a) Solar energy (b) Wind energy
(c) Tidal energy (d) Geothermal energy (e) Energy from seas can be utilized as wave, tidal or ocean
thermal energy.
214
13. What percentage of the word’s electric power and of the worlds total energy is provided by the Fossil Fuels? Fossil Fuels have been providing 66% of the word’s electric power and 95% of the worlds total energy. 14. Why coal is called a fossil fuel? Coal was formed when the plant remains got buried, hardened and chemically changed under high temperature and pressure, under the
earth’s surface. The high pressure and intense heat ultimately converted the buried cellulosic vegetable remains into coal. Therefore, it is called a
fossil fuel. 15. How coal is formed?
The formation of coal is a very low slow process. About 300 million years ago, there were dense forest in the wetlands that got buried under the surface of the earth due to some environmental changes such as earthquakes, volcanoes and floods. Gradually, they were covered with many layers of soil and got composed. The high pressure and intense heat
ultimately converted the buried cellulosic vegetable remains into coal. 215
16. What is Coal mainly composed of?
Coal is mainly composed of carbon along with smaller amounts of hydrogen, oxygen, nitrogen and sulphur. The percentage of carbon varies in different types of coals.
17. Give some examples of solid , liquid and gaseous fuels. Example of solid fuel: wood , charcoal, peat, and coal etc.
Examples of liquid fuel: bio diesel, hydrogen fuel, and ethanol. Examples of gaseous fuels: methane, propane, and hydrogen etc. 18. What is coalification? How much time it takes to form one metre thick seam of coal? The process of coal formation is termed as coalification.
To make one metre thick seam of coal 10-30 metres thick plant material is needed.
19. What is carbonization? The formation of
coal from vegetable matter is known as
carbonization. 216
20. What is known as the carboniferous age? When was it? The longest coal forming age was known as the carboniferous
age which was approximately about 280 - 450 million years ago. 21. How coal is classified? Coal can be classified on the basis of amount of carbon it contains and the amount of heat energy it can produce. 22. On which factors, types of coal depends?
The type of coal formed depends on the vegetation that got buried under the depth at which the coal seams were formed. 23. What are the types of coal ? How much percentage of carbon
is contained by each type of coal? •
Peat - 27% of carbon.
•
Lignite - about 28% - 30% of carbon
•
Bituminous coal - approximately 78% - 87%.
•
Anthracite -approximately 94% - 98%. 217
24.What is peat?
Peat is a spongy type of organic matter with a lot of fibre. It is considered as the earliest stage in the formation of coal and the topmost layer in the coal-forming environment. The cellulose of the plant material is still evident in it. There may even be the roots of living plants in the layer. When this is buried, as a result of
temperature and pressure changes, the peat slowly turns into the matter which is richer in carbon.
25. What is lignite? lignite is the young stage of the coal formation. It has about 28% 30% of carbon. It is also has a lot of fibrous matter and has high
moisture content. It has the lowest energy content and hence, its value as a fuel is low. It is also known as brown coal.
26. What is Sub-bituminous coal? Sub-bituminous coal yields more energy than ignite on burning. It is a dull black in colour. 218
27. What is bituminous coal? Bituminous coal is the most commonly used coal because of its
higher heating value. It is shiny black in colour and has low moisture content. Its carbon content is approximately 78%87%.
28. What is Anthracite ? Anthracite is the best form of coal. It has very less moisture
content and it is also known as smokeless coal. The amount of carbon in the anthracite is approximately 94% - 98%. 29. In which parts of the world coal deposits are mostly found?
Coal deposits are found in almost all parts of world – Europe, Asia, Australia, North America and in the Arctic regions. 30. Where these deposits are found?
These deposits are found as sedimentary rocks, sandwiched between sandstone and shale. 219
31. What is the estimated reserves of coal in the world? The estimated reserves in the world amount to 1001 billion tons,
enough to last 180 years at the present rate of uses. 32. In which parts of the India coal deposits are mostly found In India, coal reserves are mainly found in West Bengal, Odisha,
Jharkhand, Andhra Pradesh, Bihar and Madhay Pradesh. 33.
When
the
Jharia
mines
in
Jharkhand
started
coal
production. The Jharia mines in Jharkhand started coal production in 1894. 34. What do you know about Tower Colliery?
The oldest and continuously working deep mine in the UK, and possibly in the world, is Tower Colliery at the northern end of South Wales valley. This colliery was started in 1805 and, at the
end of 20th Century, it was brought by its miners thereby preventing its closure. 220
35. Draw a map of India and show states having coal deposits?
221
36. Describe with a neat sketch the process of destructive Distillation of coal.
The Destructive Distillation of coal is carried out when coal is strongly heated in the absence of air at a temperature of 1273 K. During this process, coal breaks down into various components
such as coal gas, ammoniacal liquor , coal tar and coke.
destructive distillation of coal 222
37. What is Coal Gas? What are its uses? Coal Gas is a composite mixture of gases such as hydrogen
(50%), carbon monoxide (8%), methane (35%) along with other gases. Coal gas is considered as a good fuel due to its high calorific value. Earlier coal gas founds its used as cooking gas
and for street lighting purposes. These days it is
used in
industries as fuel. Since Coal gas is contains hydrogen, it is
also used to create a reducing environment for many chemical and metallurgical processes. 38. What is Ammoniacal Liquor? What is its uses?
It is a solution of ammonia in water. When it is treated with sulphuric acid, it forms ammonium sulphate which is used as fertilizer. Ammonium superphosphate is also used as fertilizer.
223
39. What is Coke? What is its uses?
It is a solid carbonaceous material (with 98 % carbon) derived from destructive
distillation
of
low
ash,
low
sulphur
containing
bituminous coal. After the elimination of coal gas and coal tar, coke
is left behind. It is an almost pure form of carbon. Coke obtained from coal is grey, hard and porous. Coke with less ash and sulphur
content is quite highly priced in the market. It burns without smoke. It is used as a fuel and as a reducing agent in smelting iron ore in a blast furnace. Coke is used to manufacture fuel gases like water gas [a mixture of hydrogen (H2) and carbon monoxide (CO) , producer gas [a mixture of carbon monoxide CO, hydrogen (H2) and
nitrogen (N2)], wood gas etc. These gases have a wide variety of application in chemical industry. Coke is used as a starting material
to make acetylene (C2H2) gas, acetic or ethanoic acid (CH3COOH) and plastics such as polyvinyl chloride (PVC). Coke is also used to reduce the oxides of iron and zinc to the respective metals. 224
40. What is Coal Tar ?
It is a viscous brown or black liquid produced by the destructive distillation of bituminous coal. It smells of naphthalene. It is a complex mixture of
about 200 organic compounds (mainly hydrocarbons). These include naphthalene,
tolune,
benzene,
phenol,
aniline
etc.
These
organic
compounds can be easily separated by the process of fractional distillation of coal tar. The composition of coal tar are generally varies according to
the variety of coal used, temperature and equipment used. 41. What are the uses of coal tar?
Coal tar was once regarded as a useless nuisance. These days, however, it has led to a whole new field of chemistry and its compounds are indispensable to a vast number of products such as drugs, dyes, explosives, perfumes, preservatives, paints, insecticides etc. As it is inflammable, it is sometimes used for heating. Coal tar can also be used in medicated shampoos, soaps and ointments. It is used for making waterproofs roofs and certain insulating compounds. The residue left behind after fraction distillation of coal tar which is used to surface the roads. Bitumen, a petroleum product, is also used for this purpose. 225
42. What are the uses of coal? Coal does not find use only as a fuel. It has a variety of users in
the modern industrial civilization. The various uses of coal are given below•
The chemical energy stored in coal is used to heat water to
produce steam the turns the turbines rotating electromagnets, which in turn generates electricity in thermal power plants.
Majority of power station in Britain use coal as their energy source. •
Coal is used as a fuel for domestic and industrial needs because it burns easily and has a high calorific value.
•
Coal is used to make fuel such coal gas, synthetic petrol,
methane and coke. •
Coal
is
used
to
manufacture
industrially
useful
organic
compounds such as benzene, naphthalene etc •
Earlier coal was used to run trains with steam engines. 226
43. What is petroleum? Why is it called as black gold? Petroleum is a naturally occurring oily liquid found under the surface of the earth. It is a mixture of hydrocarbons. Petroleum is extremely important for
the economy of the nation as it is a versatile source of energy. It is often called black gold.
44. How petroleum are formed? It is formed by the decomposition of marine microorganisms. Dead tiny
microorganisms and tiny plants that lived in the sea, settled on the ocean beds. All these got buried deeper under the hundreds of feet of sand, clay and
silt brought down by the rivers. As additional sediments piled up over a long period of time, the pressure increased and the temperature rose in the layers
below. Under such conditions, the deposits got converted into fossil fuel reserves by the catalytic action of bacteria, in the absence of water. The
buried organic matter broke down into simpler hydrocarbons (compounds made up of carbon and hydrogen only), both are gaseous and liquid. Due to
the movements in the earth, the mixture of hydrocarbons got trapped between the impenetrable layers of hardened mud and sand. These layers prevent the
oil from oozing out of the surface. This oil is called petroleum. 227
45 How much of the decaying organic matter gets converted into
petroleum.? Only 2% of the decaying organic matter gets converted into petroleum.
46. What ‘petroleum’ literally means? What is its other name? The word ‘petroleum’ literally means oil from the rocks. It is derived
from Greek words petra (rock) and oleum (oil). It is also called mineral oil. It is also called crude oil. 47.Write the properties of petroleum. petroleum or crude oil is dark brown or even green coloured viscous liquid with an unpleasant smell. It is not miscible with
water, it floats on water. 48. Where Natural gas is found?
Natural gas naturally occurring under the surface of the earth occurs above the crude oil, and water below it, trapped between the impervious rocks. 228
59. What are the uses of petroleum? It is
a source
of
chemicals
for manufacturing
fertilizers,
pesticides and plastics. 50. Where the petroleum deposits are mostly found in India?
In India, petroleum or crude oil is found in coastal regions and in the rivers basins. Petroleum was first discovered in India at Digboi in Assam. Oil reserves in India are found in Assam
(Lakuwa and Rudrasagar) and Gujrat (Ankaleswa and Kalol), Haldia, Mumbai, Vishakhapatnam, Kochi , Kandla, Chennai and
Hazira also have all reserves. This precious oil is also likely to be found in Andaman, Punjab, Kutch , Tripura, Manipur and West Bengal.
51. Which are the major oil producing countries in the world? The major oil producing countries in the world are Saudi Arabia, Iran, Iraq, Russia, the US, the UK, Mexico and China. 229
52. Which countries the petroleum deposits are mostly found in world?
Petroleum reserves are found in many countries of the world but the Middle East countries topped the list.
53. Where petroleum was first discovered in India? Petroleum was first discovered in India at Digboi in Assam. 44. Where the oil deposits under the seabed in India are
found? The oil deposits under the seabed in the offshore areas in
India are found in Bombay High as well as the offshore deltas of Godavari and Kaveri. 55. Where The word first oil well was drilled?
The word first oil well was drilled in pennysalvania, USA in the year 1859. 230
56. How petroleum be extracted?
Petroleum can be extracted from the earth by drilling an oil well. Drilling may even reach a depth of 10,000 feet . An oil well is drilled by using a drilling rig, a large structure with equipment
for drilling. When an oil well drilling reaches the required depth, natural gas comes out first with a great pressure and even petroleum comes along due to gas pressure. After the grass
pressure subsides, petroleum has to be pumped out of the well with special equipment. Earlier drilling for petroleum was done
only on land. Later, new technology was developed for drilling under the seabed. This crude oil is then transported to the refinery through pipelines
57. Where offshore drilling is done In India? In India offshore drilling is done in the Bombay High area at a distance of about 150 kilometres to the West of Mumbai city. 231
58. What is petroleum refining?
Crude oil is complex mixture of several hydrocarbons and cannot be used in the form it is obtained. It is necessary to separate petroleum into smaller fractions of hydrocarbons by a process
known as petroleum refining or petroleum fractionation. Refining of petroleum may be defined as the process of separating different
useful fractions from petroleum with simultaneous removal of the undesirable impurities by the process of fractional distillation. This is done by the fractional distillation of the crude oil in big factories called petroleum refineries 59. How many petroleum refineries are in India? Where they are
located? Where is the oldest refinery in India was set up? There are more than 17 petroleum refineries in India. Some of them
are located at Guwahati, Digboi, Barauni, Haldia, Mumbai, Kochi, Chennai, Visakhapatnam and Mathura. The oldest refinery in India was set up at Digboi in Assam in 1901. 232
60. Describe the process of refining of petroleum by fractional distillation with a neat diagram.
The process of refining of petroleum by fractional distillation is based on the fact that different fractions of the crude oil boil within the different temperature ranges are collected separately. It is carried out by hitting petroleum in a furnace at a temperature of 400C. The oil vapours rise into the fractioning
column (tall cylindrical structure) made of steel, known as distillation tower and get cooled. The tower contains a series of shallow trays that collect the liquid at the vapours condense.
The liquid on each tray is then piped off. The vapours of the higher boiling point fractions condense first near the base of the
fractionating coil, depending on their boiling point ranges. (Diagram is given in next slide) 233
The vapours of the fractions with lower boiling point condense at different heights in the fractionating column. The process is
carried out till the crude oil is separated into five or six fractions Each fraction has a different range of boiling point.
The uncondensed vapours pass out at the top of the column.
234
61. Write the name and boiling point of various fractions which are
obtained
petroleum.
from
fractional
Fraction
Petroleum gas Petrol and naphtha (Gasoline)
distillation
of
refining
of
Boiling point range < 40C 40C - 170C
Kerosene
150C - 240C
Diesel oil
220C - 350C
Lubricating oil
> 350C
Fuel oil
> 500C
Paraffin waxes
Solid
Bitumen
Solid
235
62. Write the uses of various fractions which are obtained from fractional distillation of refining of petroleum.
Fraction Uses Petroleum gas Fuel, used as such or liquefied into LPG* Petrol and naphtha Fuel for cars, chemicals for factories, (gasoline) aviation fuel, solvent for dry cleaning and insecticides. Kerosene Special grade kerosene is used to jet fuel. Household fuel is for used for cooking or for lightning lanterns. Diesel oil Fuel or automobiles, train engines and electric generators. Lubricating oil Polishes and waxes, oil for lubricating machinery. Fuel oil Fuel for ships and power stations. Paraffin waxes Candles polishes, ointment, vaseline, wax, papers, waterproofing materials and gases. Bitumen Tar for roads, pains and waterproofing materials for roofs. 236
63. What is LPG ?
LPG is a Liquefied Petroleum Gas, It is liquefied under pressure, and filled in cylinders to be supplied for domestic use. LPG
consists of mainly butane (C4H10). It is highly volatile and comes out as gas when the knob of the cylinder is turned on and burns easily in the burner with a blue flame.
64. What are known as petrochemicals? What are their uses? Give some examples of petrochemicals.
Petrochemicals are the organ compounds obtained from the various petroleum fractions and natural gas. hese compounds are useful in the preparation of a wide range of material such as plastics, fibers, dyes, medicine, pesticide, explosives, detergents and other such compounds.
Some examples of petrochemicals are benzene, ethylene, tolune, methyl alcohol, formaldehyde, acetone, acetic acid and hydrogen. 237
65. What are petroleum based plastics? Polythene, polyvinyl chloride (PVC) and Bakelite are petroleum based plastics. 66. What is the role natural gas in agriculture?
Hydrogen gas obtained from natural gas is used in the manufacture of fertilizers such as ammonium nitrate and urea which are
indispensable for agriculture. 67. What is the India’s current oil reserves? India’s current oil reserves are about 5 million barrels and 30% of
its energy needs are met through oil. 68. What is the need to produce synthetic petroleum and synthetic
coal? how they are produced? The oil reserves are limited and are first depleting with modern usage. This has created a need to produce substitute like synthetic petroleum for machines and vehicles. Petroleum hydrocarbons are refined to a desired purity to produce synthetic fuel. 238
69. What are synthetic fuel or synfuel? What are Synthetic fuel or synfuel is any liquid fuel obtained from
coal, natural gas or biomass. Synfuel sometimes refers to fuels derived from other solids such as oil shales, tar sands, waste plastics or from the fermentation of biomass.
70. Which is the situation that initiated the need to produce synthetic fuel or synfuel?
Acute shortage of liquid fuels at the time of world wars had initiated the need for this technology. 71. What are process to prepare synfuel?
Berguis process, Carrick process and Fisher Tropsch process (Coal to liquid technology or CTL technology), are some of the few methods used to prepare synfuel.
239
72. When coal to liquid (CTL) technology was used and in which country?
The coal to liquid (CTL) technology was used in South Africa to meet its energy needs during its isolation under apartheid. This process has received renewed attention in the quest to produce low-sulphur containing diesel fuel in order to minimise the environmental impact from the use of diesel engines.
South Africa has been producing fuels by the CTL technology since 1955 and is the only country in the world today to have a commercial CTL plants.
73. How Synthetic (artificial) coal are produced? Synthetic (artificial) coal has been produced in the laboratory for
subjecting peat to a high pressure of 40 megapascal and a maximum temperature of 60C which is attended gradually. Instead of peat , lignite can also be used. 240
74. The carbon-dry synthetic process? Why this process is oreferred over other processes ? The carbon-dry synthetic process involves converting high-moisture,
high-sulphur and high nitrogen containing sub-bituminous coal into high calorific value coal with low moisture, low suplhur and low
nitrogen content. Carbon-dry synthetic process is preferred over others as the temperature involved is between 400 F to 700 F (204C-370C) and
the process can be carried out at ordinary atmospheric pressure. 75. What is natural gas ?
Natural gas is a gaseous fuel consisting of primarily of methane, CH4 (70 % to 90 %) but also includes significant quantities of other hydrocarbons. It is found in oil fields either in dissolved form or in isolated form in national gas fields and coal beds. It is often informally referred to as simply gas, especially when compared to
other energy sources such as electricity. 241
76. Why before use of natural gas it has to be undergo extensive processing?
Before natural gas can be used as a fuel, it must undergo extensive
processing to
remove
all
materials
other than
methane.
77. What is dry natural gas? Natural gas consisting only of methane is called dry natural gas.
78. What are the disadvantages of natural gas to use? The major difficulty in use of natural gas is a storage and
transportation because it’s low density. Natural gas pipelines may be economical but impractical for transportation across oceans.
242
79. What are the uses of Natural gas? Natural gas is a major source of electricity generation in
thermal power plants through the use of gas turbines and steam turbines. It burns cleaner than other fossil fuels and produces less carbon dioxide per unit energy released. Compress natural gas CNG
is an environmentally cleaner
alternative to other automobile fuel such as gasoline and
diesel. CNG is being used in public transport vehicles to reduce air pollution in cities. 80. Why Compress natural gas safer than other motor fuels in
the event of if fuels spill? It is also safer than other motor fuels in the event of if fuels
spill because being lighter than air. It disperses quickly.
243
81. Where network of natural gas pipelines exists in India? A network of natural gas pipelines exists in some parts of Delhi and Vadodara (Gujrat). 82. Where India has the reserve of natural gas? India has a very vast reserve of natural gas in Tripura, Rajasthan, and Maharashtra and in the Krishna-Godavari delta.
83. What is renewable source of energy? Give some examples of is renewable source of energy.
Renewable source of energy can produce energy continuously in nature and are almost inexhaustible, at least as long as the life exists on this
earth. Renewable energy sources include wood, wind water, geothermal power, tidal waves and solar energy.
244
84. What is non-renewable source of energy? Give some examples of
is non-renewable source of energy. non-renewable source of energy have accumulated over ages and
hence
ones
exhausted,
cannot
be
quickly
replenished.
Non
renewable energy sources are crude oil (petroleum), natural gas, coal and uranium.
85. Why there is an urgent necessity of, renewable and nonconventional sources of energy?
Presently, the rate at which the non-renewable sources of energy are being consumed is higher than the rate at which they are formed. It is estimated that their stocks are likely to be exhausted by the middle of the 21st century. Hence, there is a likelihood of an energy crisis. For avoiding the problem of an energy crisis, scientists
all over the world are trying to find ways and means of getting all types of energies from the alternative sources, that is, renewable
and non-conventional sources. 245
86. What is MNRE? What is its function? MNRE stands for Ministry of Renewable Energy. Its function is to tap the alternative sources of energy. It has tapped nearly all sources of energy
like solar energy, wave energy, wind and energy from biomass and water.
87. What we need to do for conservation of energy? The things that can be done for the conservation of energy are given below•
Use only renewable energy sources.
•
In domestic stoves, use high efficiency which burn with a blue flame (indicating complete combustion producing more heat) and not with
a yellow flame (indicating incomplete combustion, producing less heat).
•
Use vessels with a flat bottom for heating instead of vessel with a round bottom.
•
Use energy saving devices like pressure cookers for cooking.
•
Use casseroles for keeping their eatable hot instead of hitting them again and again. 246
•
Cover the vessel while cooking vegetables, dal , meat, etc to prevent heat loss and, the liquid start boiling reduce the
flame. •
Use solar cookers and solar water heaters, wherever possible.
•
Switch off lights and fans when not in use.
•
Use room heaters, coolers and air conditioners only when
absolutely necessary. •
In winters sit in the sun to warm you instead of using a heater inside the room.
•
Use Compact Fluorescent Lamps (CFL’s) LED bulbs and tube
lights,
which
consume
less
energy,
instead
of
incandescence lamps.
•
Plants trees along with the roads. 247
88. What is PCRA? What are the tips given by them for conservation of while driving?
In order to save petrol/diesel while driving, the Petroleum Conservation
Research
Association
(PCRA)
has
given
the
following tips.
•
Always drive a moderate and constant speed
•
While waiting at the traffic signals or anywhere else, switch
the engine off. •
Keeping the tyre pressure of your vehicle perfect.
•
Ensure regular maintenance of the vehicles.
All the above situation would not only be ensure the longevity of the vehicles but would also help in saving the energy reservoir for the future generations.
248
Back to contents 249
1. Which species are known as flora and fauna? Ans. The species of plants taken all together is known as flora.
Similarly, the species of animals taken together is known as fauna. 2. How men are dependent on the living world for their survival?
Ans. For food , medicine, fibers, timber, rubber and even clothes human beings is dependent on the living world for their survival . 3. Which is the most serious aspect of the loss of biodiversity
Ans. The most serious aspect of the loss of biodiversity is the extinction of species
4. What are the natural causes of deforestation of forest? Ans. Natural causes of deforestation are forest fires and severe droughts.
5. How deforestation resulting in droughts? Ans. The increase in temperature of the earth disturbs the water
cycle. This may reduce the rainfall, resulting in droughts. 250
6. How deforestation resulting in desertification? Deforestation results in soil erosion and degradation of land.
Loose soil particles get transported with surface run-offs. This leads to the removal of the top fertile soil and exposure of hard and rocky layer of soil. Gradually, with the loss of fertility , high wind velocity, low rainfall and extremes of temperature, the fertile land converts into deserts. This is called desertification.
7. How Denudation leads to serious problems of floods? Ans. Denudation in the catchment areas of rivers leads to serious problems of floods.
8. How Deforestation decrease the ground water level ? Ans. Deforestation causes decrease in rainfall and also reduces
the water holding capacity of the soil and movement of water from the soil surface into the ground. This decreases the ground water level. 251
9. What are the causes of destruction of natural habitat ? Ans. The causes of destruction of natural habitat are
• House Construction • Dam construction
• Setting up of industries • Road construction • Cutting of trees for timber and fuel wood.
• Overgrazing by cattle 10.
What was the result of introduction of exotic predatory fish,
Nile perch, into the Lake Victoria in South Africa? Ans. As exotic predatory fish, the Nile perch, was introduced into Lake Victoria in South Africa, it threatened the entire ecosystem of
the lake by eliminating several native species that were endemic to this lake.
252
11. People of which part of India practice Jhum or shifting
cultivation? Ans. In India, the people of Eastern and Northern Eastern region practice Jhum or shifting cultivation on hill slopes. About 85% of the
total cultivation in the North East India is by shifting cultivation. 12. When IUCN red list was initiated ?
Ans. It was initiated in 1963. 13. What are Rare and Threatened species? Ans. Earlier , species were commonly considered only under the following two categoriesRare Species - These are the species with a small population
worldwide, usually a number less than 10,000, not presently endangered or vulnerable but at risk.
Threatened species- These are species which are now listed in the categories - endangered, vulnerable or rare. 253
14. Give three examples of each of the following Red List Categories species-
(i) Extinction (EX), (ii)
Extinct in the Wild (EW) , (iii) Critically
Endangered , (iv) (CR) Endangered (EN), , (v) Vulnerable (VU) , (vi) Near Threatened (NT) , (vii) Least concern (LC) Ans. Extinction (EX) - Dodo, Thylacine and passenger pigeon. Extinct in the Wild (EW) -
Abingdon Island tortoise, Red tailed
black shark and South China tiger, Critically Endangered (CR) - One horned Rhino, Jerdon’s courser , Arakan forest Turtle
Endangered (EN) – Indian rhinoceros, crocodile, blue whale Vulnerable (VU) - Cheetah, gaur, lion
Near Threatened (NT) Small- clawed otter , blue-billed duck, bald eagle. Least concern (LC) - Brown rat , mountain quail and wood pigeon 254
15. Write the one word substitute of the following 1. The variety and variability among living organisms and their
ecological complexes. 2. Destruction of forest cover of India due to cutting of trees 3. Conversion of fertile land into deserts.
4. The species restricted to a particular area or region 5. New species entering a geographical region
6. The species whose no member is alive and whose chances for further evolution are lost 7. Long compilation of rare and endangered species that is
maintained by IUCN 8. The division of large continuous areas of habitat into two or more fragments.
255
16. Clearing of patch or areas of land in the forest by burning the natural vegetation to carry out cultivation for two years till
the yield begins to decline and then shift into a new area Ans. 1. Biodiversity,
2. Deforestation , 3. Desertification, 4. Endemic Species,
5. Exotic Species, 6. Extinct species,
7. Red Data Book, 8. Habitat Fragmentation, 9. Shifting cultivation.
256
17. Describe the causes and consequences of deforestation.
Consequences of deforestation Cutting of trees may have following serious consequences.
(i)
Golbal
warning
Deforestation
has
caused
a
serious
imbalance of Oxygen (O2)and Carbon dioxide (CO2) in the atmosphere. You know that plants take up carbon dioxide for
photosynthesis.
As deforestation decreases the number of
trees , the level of carbon dioxide in the atmosphere increases. This leads to global warming as carbon dioxide traps the heat of the sun’s rays. (ii) Draughts - The increase in temperature of the earth
disturbs the water cycle. This may reduce the rainfall, resulting in droughts. 257
(iii) Desertification - Deforestation results in soil erosion and degradation of land. Loose soil particles get transported with surface run-offs. This leads to the removal of the top fertile soil
and exposure of hard and rocky layer of soil. Gradually , with the loss of fertility , high wind velocity, low rainfall and extremes of
temperature, the fertile land converts into deserts (iv) Floods- Denudation in the catchment areas of rivers leads to serious problems of floods.
(v) Decreases in the ground water level - Deforestation causes decrease in rainfall and also reduces the water holding capacity of the soil and movement of water from the soil surface into the
ground. (vi) Deforestation leads to the extinction of many wild animals and
plants. Deforestation will also cause shortage of forest productsfirewood, timber , honey gum, sealing wax, paper , etc. 258
18. Why there is an urgent need for conservation of biodiversity? Ans. In recent years, the biodiversity of our planet has declined
markedly, mainly due to human practice such as deforestation, pollution, toxic wastes and industrial expansion. This rapid decline in biodiversity has led to serious problems such as global
warming zones, ozone layer depletion and natural resource exhaustion. Thus, there is an urgent need for conservation of
biodiversity 19. What conservation of our biodiversity refers to? And what for it aim to?
Conservation of our biodiversity refers to human efforts to correct, reverse or prevent or put an end to those activities that are causing decline in biodiversity. The aim is to prevent
endangered species from extinction. 259
20. What is the most effective and efficient mechanisms for conserving biodiversity?
Ans. The most effective and efficient mechanisms for conserving biodiversity is to prevent further destruction or
degradation of natural habitats. 21. Name the basic strategies of biodiversity conservation? There are two basic strategies of biodiversity conservation
(a) In Situ Conservation Strategies (b) Ex Situ Conservation strategies
260
Basic strategies of biodiversity conservation (figure 7.8) Biodiversity conservation In Situ conservation Protected areas
Wildlife Sanctuaries, National parks
Ex Situ conservation Seed banks
Botanical Gardens, Zoological Gardens
Biosphere Reserves
261
22. Explain (a) In Situ Conservation Strategies (b) Ex Situ Conservation strategies
Ans. (a) In Situ Conservation Strategies - These strategies deal with conservation of living organisms through their maintenance
within their natural habitats. These include an extensive system of
protected
areas
such
as
national
parks,
sanctuaries,
biosphere reserves and forest reserves. (b) Ex Situ Conservation strategies- Ex Situ conservation implies the conservation outside the natural habitats. These Include
zoos, botanical gardens, seed banks and gene banks.
262
23. Which are called protected areas? Give same examples. Protected areas are areas of land or sea specially dedicated to
the protection and maintenance of biodiversity.
Examples
of protected areas are National parks, wildlife sanctuaries and
biosphere reserves. How protected areas are managed These are managed through legal means and have been set up
within the legal framework of Indian Wildlife (Protection) Act 1972.
263
24. Which are called National parks?
A national park is a large area dedicated to conserve •the environment,
•natural resources and •the wildlife 25. What are the features of a national Park?
In a national park. • private rights of non existent. • forestry operations, grazing of animals, fishing and hunting of
animals are prohibited. • the visitors are allowed to enter only for study, cultural and
recreative purposes • the exploitation habitat for wildlife is banned. 264
26. Match the following column
National Park
City, State
1. Kanha National Park
(a) Junagadh Gujarat
2. Corbett National Park
(b) Sawai Madhopur, Rajasthan
3. Simlipal National Park
(C) Mandla, Madhya Pradesh
4. Gir National Forest
(d) Jorhat, Assam
5. Bandipur National Park.
(e) Mayurbhanj, Odisha
6. Ranthambore National Park (f) Mysore, Karnataka
7. Kaziranga National Park
(g) Nainital, Uttarakhand
Ans. 1- (c), 2 (g), 3 (e) , 4 (a) , 5 (f), 6 (b), 7 (d) 265
27 Name any three animal conserved by each of the following National park(i) Kanha National Park, (ii) Corbett National Park (iii) Simlipal National Park (iv) Gir National Forest (v) Bandipur National Park. (vi) Ranthambore National Park (vii) Kaziranga National Park
SN
National Park
Animals Conserved
1
Kanha National Park
Tiger, Chital, Sambar, sloth beer, barasingha
2
Corbett National Park
Tiger, Panther, elephant, deer, python antelope.
3
Simlipal National Park
Tiger , leopard , Sambar , Elephant , chital, wild boar
4
Gir National Forest
Asiatic lion, panther, hyena, chinkara
5
Bandipur National Park.
Elephant, Tiger, Jackal , gaur
6
Ranthambore National
Tiger, leopard, hyena. Nilgai, Green pigeon, Macaque.
Park
7
Kaziranga National Park
Rhinoceros, wild buffalo, elephant, tiger 266
28.Which are called wildlife Sanctuaries? A wildlife sanctuary is similar to a national park. However, it aims only at conservation of the species.
29. What are the features of wildlife sanctuaries ? The wildlife sanctuaries are the following features -
•
The borders of the sanctuaries are not limited by state legislation
•
It is a protected area for the protection of wild animals in
their natural habitat. •
In a sanctuary, no human activity is allowed which disturbs the wildlife or their natural habitat
•
Cultivation of land and building houses is not allowed
•
A wildlife sanctuary is not for recreation and enjoyment of
the public. It does not allow easy access to the visitors. 267
•
The Killing, hunting or capturing of any species any species is prohibited except by or under the control of of highest authority in the department which is responsible for the
management of the sanctuary. •
•
Private ownership may be allowed to continue in a sanctuary.
Forestry and other usages can also be permitted but to the extent that they do not affect the wildlife adversely.
268
30. What are the Difference between National Park and Wildlife sanctuaries ?
SN 1
National Park
Wildlife sanctuaries
A national park is a large A wildlife sanctuary is similar area dedicated to conserve to a national park. However, it
the
environment,
natural aims only at conservation of
resources, and the wildlife the species. therein.
2
The
borders
of
the The borders of the sanctuaries
sanctuaries are limited by are state legislation.
3
private existent.
rights
not
limited
by
state
legislation
of
non Private allowed
ownership to
may
continue
in
be a
sanctuary. 269
SN
4
National Park
Wildlife sanctuaries
the visitors are allowed no
human
activity
is
allowed
to enter only for study, which disturbs the wildlife or their cultural and recreative natural
purposes.
habitat,
A
wildlife
the sanctuary is not for recreation
exploitation habitat for and enjoyment of the public. It
wildlife is banned
does not allow easy access to the visitors
5
forestry
grazing
operations, Forestry and other usages can
of
animals, also
be
permitted
but
to
the
fishing and hunting of extent that they do not affect the animals are prohibited.
wildlife adversely.
270
31. Match the following column
Wildlife sanctuary
City, State
1. Manas wildlife sanctuary
a. Alwar Rajasthan
2. Periyar wildlife sanctuary
b. Jalpaiguri West Bengal
3. Debrigarh
c. Barpeta, Assam
4. Sariska Wildlife century
d . Bargarh, Odisha
5. Mudumalai
e. Idukki, Kerala
6. Jaldapara
f. Nilgiris, Tamil Nadu
7 . Dachigram
g . Srinagar
Ans. 1- (c), 2 - (e), 3 - (d) , 4 - (a) , 5 - (f), 6 - (b), 7- (g) 271
32. Name any three animal conserved by each of the following Wildlife sanctuary
(i) Manas wildlife sanctuary, (ii) Dachigram (iii)Periyar
wildlife
sanctuary (iv) Debrigarh (v) Sariska Wildlife century (v) Mudumalai
(vii) Jaldapara SN
Wildlife Sanctuary
Animals Conserved
1
Manas wildlife sanctuary
Elephant, tiger, gaur, golden langur , rhinoceros
2
Dachigram
Ibex, goat, black bear, golden eagln, hangul
3
Periyar wildlife sanctuary
Elephant, barking deer, gaur sambar
4
Debrigarh
Leopard, sambar, bison, hayna chital, chinkara
5
Sariska Wildlife century
Tiger, Jungle cat, hyna, chital
6
Mudumalai
Elephant, gaur, flying squirrel, Sambar
7
Jaldapara
Rhinoceros, elephant, Indian bison, variety of birds 272
33. Which are called Biosphere Reserves? Biosphere reserves are areas dedicated for preservation of •
Cultural and traditional lifestyle of the tribal people of the area
•
Biodiversity of the region,
•
Genetic resources of plants and animals, and
•
Natural ecosystems in the area.
34. What are the features of Biosphere Reserves? •
It may contain other protected areas in it too, such as National park and Wildlife sanctuaries.
•
Cultivation of land and building houses is permitted in the peripheral areas
•
The economic activity of the people and protection of biodiversity regions are managed.
•
Commercial exploitation of natural resources is not permitted.
However, tourism is allowed in the peripheral areas of the reserves 273
35. Name some of the important Biosphere Reserves of India and the states in which they are located.
Biosphere
State
Nanda Devi
Uttarakhand
Sundarban
West Bengal
Pachmarhi
Madhya Pradesh
Nilgiri
Junction of Tamil Nadu, Kerala and Karnataka
Kaziranga
Assam
Kanha
Madhya Pradesh
Rann of kutch
Gujarat
274
36. Why conservation of Forest is important task ? Much of the diversity is present in the forest areas. Forests
contribute to the economic development of a country by providing goods and services to the people. They play a vital role in maintaining the oxygen supply in air we breathe and in regulating the climatic conditions. Therefore conservation of forests becomes necessary and the most important task.
37. Based on the importance of forests how forests are classified ? Keeping in view the importance of forests, these are classified
into three types:(a) Reserved forest,
(b) Protected forests and (c) Unclassed forests. 275
38. Which are called Reserved forest Reserve forests are those which are protected by the Government
of India. Land rights to these forests are typically acquired by the Government of India. In such forests rights to all activities such as hunting, grazing etc are banned unless specific orders are issued otherwise.
However,
such
rights
are
sometimes
given
to
communities who depend on the forests for their survival.
Typically reserve forests are often upgraded to the National Park status. 39. Give one Example of upgradation of National Park to a reserve
forest. Sariska National Park was declared a forest in 1955, upgraded to
the status of a wildlife sanctuary in 1958 and became a tiger reserve in 1978. 276
40. Which are called Protected forests? Protected forests are similar to reserved forests except that
hunting, grazing, etc are allowed unless specific orders are issued otherwise.
41. What are the kinds of Protected forests? There are of two kinds Protected forests •
demarcated protected forest
•
and intercalated protected forest
These are based on whether the limits of the forest have been
specified by a formal notification. 42. Which are called Unclassed forests? Unclassed forests:
•
They are large inaccessible forests
•
Many of these are unoccupied
They are ecologically and economically less important 277
43. What are the strategies can be adopted to prevent the depletion of
forest cover in the reserved forests? The strategies are1. The use of firewood for cooking food should be discouraged. 2. The villagers should be provided with some alternate environmentalfriendly sources of energy such as biogas.
3. An extensive reforestation/afforestation programme should be followed by the practice of renewing the forest by planting seedlings
or small trees. 4. Forest fires, a major cause of destruction of the forest cover, should be controlled immediately by using aircrafts which spray fire
extinguishing solution over the burning forest 5. Overgrazing by cattle should be prevented.
44. What is called as natural reforestation If the deforested area is left undisturbed , it reestablishes itself. This process is called natural reforestation 278
45. Write short notes on (a) Project Tiger At the time of Independence, there were 30,000 tigers in India.
The number dwindled to only 1827 in 1972. decline in Tiger population is mainly due to hunting for its skin and bones In
response to the alarming decrease in tiger population, an operation called “Project Tiger” was initiated on April 1, 1973. The objective of the project was to conserve the animal and
preserve its habitat. The project was initiated with nine tiger reserves located in nine different states. The project was initially successful and a number of tigers increased gradually to 4200 in
the early 1990s but their number came down to 3500 in 2002. In 2006, all the 16 tigers in Sariska Tiger Reserve reported to have
been killed by poachers and hunters. 279
46. (b) Chipko Movement In 1970, Gopeswar and some 20 villages of the Tehri-Garhwal
district of Uttar Pradesh (now Uttarakhand) were devastated by floods due to deforestation. The villages, under the leadership of Chandi Prasad Bhatt, pledged that they would not let any feeling
of trees. They wanted to save the trees even at the cost of their
lives. Woman started hugging the trees when the forest
contractors tried to cut them down. The forest were, thus saved because of this hugging act. This
movement
called
Chipko
Movement,
became
very
successful and was popularized all over the world by Sunderial Bahuguna. The movement advocates the slogan of planting trees for 5 Fs- Food, Fodder, Fuel, Fiber and Fertilizers.
280
(c) Recycling of paper Paper is one of the important products that we get from the
forest. One tone of paper is made out from 17 full grown trees, thus by saving one paper , in a day, many trees can be saved in a
year. All kinds of used papers, packing boards, etc. can be recycled at least 5-7 times to form fresh writing paper. This will not only save our trees but also save energy and the water
required to manufacture paper. Also, it will reduce the problem of garbage disposal and pollution caused by the industries that are
manufacturing paper.
281
(d) When National Forest policy implemented by Government of India? What is the objective of This Policy.
Government of India implemented the National Forest policy in 1952, which aimed at increasing the forest coverage to one
third of the total land area of the country. The Indian Government
revised this policy in 1980. This act aimed at
preservation and conservation of the natural forest along with
meeting the basic needs of the people. 47. Which are called Zoological Gardens?
Zoological gardens or parks or zoos are places where the wild animals are kept in a protected environment on the human care for public display. As far as possible, all the animals in a
zoo are provided with conditions similar to their natural habitats. The aim is to enable us to learn about their behaviour and food habits. 282
48. How plant species are conserved in a Botanical Gardens? Botanical gardens play an important role in the conservation of
plant species. they have collections of plants for reference. Plant species are grown for identification purposes and each of these
plants is labeled to indicate its scientific name, common name and vernacular name. 49. What is Green Book and who publish it?
Botanical Survey of India (BSI) publishes the Green book that enlists rare, endangered and endemic plant species growing in the
botanical gardens of the country. 50. What are the other methods for the conservation of biodiversity? •
The other methods for the conservation of biodiversity are establishment of
•
seed banks,
•
pollen (storage) banks and
•
tissue labs. 283
51.
Which
species are
called Endemic Species
why
their
distribution is restricted in one area.
Different parts of the world have their own flora and fauna depending on the environmental conditions prevailing In that
origin. flora and fauna of different parts of the world do not show any uniform pattern of distribution. The species which have restricted distribution and are found only in restricted areas are
called endemic species. Endemic species are not found anywhere else.
What are the reason for non uniform distribution of species and endemism. The reasons are as below :-
•
Physical Factors.
•
Climatic factors.
•
Biological Factors. 284
52. How Physical Factors affects the distribution of endemic species? Mountain ranges, large water bodies, land masses limit the
distribution of many terrestrial species, For example the Great Himalayan ranges harbour various endemic species of plants
and animals. How Climatic factors affects the distribution of endemic species
In extreme temperatures, only a few animals and plants can survive, for example the Himalayan ranges harbour a wide range of animals that can survive in extreme cold.
285
53. How Biological Factors affects the distribution of endemic species ?
Vegetation is a biological barrier that affects distribution of species. Plants serve as food and as a means of shelter for animals. Thus, depending upon the selective food habits,
animals are confined to areas that have vegetation of their choice, for primates like monkeys prefer to live in tropical forests where they feed on fruits, nuts, birds and insects.
54. What is the function of the central Zoo Authority of India? The
central
Zoo
Authority
of
India
provides
financial
assistance to zoos and also approves donations to animals, both domestic and foreign for breeding programmes.
286
55.What is Migration ? Migration includes movements of birds and other animals over
varied
distances
made
in
response
to
changes
in
food
availability, habitat or weather. 56. What are the types of migration?
Migration is of two types• Permanent migration
• Seasonal Migration 57. What is Permanent migration? This type of migration occurs due to un-favourable climatic
factors or shortage of food, water or shelter. Under the influence of these conditions, animals permanently migrate to other parts where conditions are favourable. Many species of butterfly
exhibit permanent migration. 287
58. What is Seasonal Migration? This kind of
migration occurs for food, breeding places,
favourable day length and climatic conditions. It is marked by its annual seasonality. The animals leave their original homes in a
particular season and return back once it is over. 59. Write one paragraph about Migratory birds? Some of the wetlands in India are popular for migratory birds.
During winters, birds such as Siberian cranes came in large numbers to Bharatpur (Rajasthan) and Rann of Kutch (Gujarat).
At a place where the desert merges with sea, Flamingos with their brilliant pink plumage come in thousands to build nest in mounds of mud and raise their young ones
288
60. Fill in the blanks India has 80 National parks. The earliest national parks in the US is Yellows National Park The earliest national parks in Australia is Royal National Park
In India the Jim Corbett National Park was the first one to be established. At present India has 614 protected areas out of which 100 national parks and 514 Wildlife sanctuaries. India has a rich flora. With about 47000 plant species, India is tenth
in the world and fourth in Asia in plant diversity. Reserved forest cover 54.4 % of the total forest area of 76.5 million
hectares of land. Protected forests cover 29.2% of the total forest area. Unclassed forests cover 16.4% of the total forest area
Every year, we are losing forest at the rate of 1.5 million hectares. 289
Pachmarhi Biosphere Reserve that consists of one national park and two Wildlife sanctuaries.
Till date, there are 13 biosphere reserves in India. Today, there are 27 Tiger reserves in India. In India there are 169 zoos. A famous botanical garden of India is the Indian botanical garden situated at Howrah (Kolkata).
National Botanical Research Institute (NBRI) located at Lucknow (UP) also has a large collection of plants. Ladakh’s freezing high altitude is the home for yak , the Tibetan
antelope, blue sheep and wild ass A few examples of exhibiting seasonal migration are Siberian
cranes, salmons and sea lions.
290
A. Fill in the blanks 1. The diversity can be in the form of ……. , …….. ,……….., ………… and ………… constitution.
Ans - size, structure, behaviour, habits, genetic 2. Biodiversity differs from …………….. Ans. place to place 3. The total number of species present on the earth varies from 5
to 50 million and averages 14 million. Out of these only about ………. are known and described. Ans. 50%
4. About ……….. of the known fauna are insects Ans. 85%
291
5. IUCN Red list of threatened species has recognized nine
……………………. of the species. These categories signify the …………………………… of species.
Ans. Red List Categories, conservation status 6. The presence of different forms of …………………is called biodiversity
Ans. living organism. 7.
Increasing
demands
of
………………….
have
threatened
biodiversity
Ans. human population 8. The most serious loss of biodiversity is ……………. of species.
Ans. extinction
292
9. ………………….. has resulted in destruction of habitats, degradation of environment and habitat fragmentation. Ans. Expanding human population
10. ………………… for loss of habitat due to various needs of human population has serious consequences, such as global
warming, floods , droughts and desertification Ans. Deforestation 11.
An
international
organization,
………………,
maintains
records of endangered species and rare species in the Red Data Book Ans. IUCN
12. Continuous depletion of ……………has led to serious loss of biodiversity.
Ans. wildlife 293
Back to contents 294
1. Are the variety of organisms inhabited in our earth are different on
basic character? The variety of organisms inhabited in our earth, though they look different from each other, yet their basic characteristics features, such as, they eat and digest food, respire, excrete wastes and produce their own kind, are common.
2. What constitute the organ made of living organism? Each part or organ of the body of living organisms is made up of tissues
which are group of similar cells performing a specific function. 3. What is cell? Cell is the basic structural and functional unit of all living forms. It is the basic structural unit of life. Just like a brick is a building block of the one in our house, a cell is a unit of building block of all living
organisms. A cell is considered of functional unit because it performs all the biological process such as respiration, excretion and growth
necessary for the survival of an organism. 295
4. Who discovered the cell? The cells were first discovered by an English scientist Robert
Hooke in 1665. 5. Cells have been a part of the Living Organism since the
origin of life buy why they were not studied earlier? A majority of the cells are invisible to the naked eye as they are extremely small in size, and, therefore, were not studied
earlier. 6. How cells were look like in Robert Hooke’s microscope? In Robert Hooke’s microscope cells were look like a thin slice
of dried cork and honeycomb like structures. Actually, the cells were dead cells of the cork, present in the bark of a tree.
7. Why cells are also called hollow room? Cells are like small compartments bound by firm cell walls 296
8.Who is Antonie van Leeuwenhoek ? What is his contribution towards the study of cell? Antonie van Leeuwenhoek is a Dutch scientist who in 1674, discovered the living cells under his improved microscope. The cell
studied by him were bacteria, protozoa, red cells (RBC) and other microorganisms. 9.What is range of improved microscopes? These microscopes can be used to observe objects as small as one thousand of mm (10-6 m).
10. Collect some pond water in a beaker. Take 2-3 drops of water on the glass slide and try to observe with naked eyes. Now put this
glass slide under microscope and look carefully. What do you observe? There are many kinds of organism in the pond water which are not
visible with the naked eye. A microscope magnifies the microscopic objects and organism and unable to see them. 297
11.Describe Cell theory. Cell Theory:
•
In 1838, a German botanist suggested that all plants are made up of cells.
•
In 1839, another German scientist suggested that all animals are made up of cells.
•
The above Discoveries lead to a general cell theory, which
states that the basic unit of structure and the function of all living organisms is the cell. •
Later, R. Virchow, another scientist suggested that all cells
arise from pre-existing cells by cells division. •
Now, a cells is regarded the smallest unit of life. A cell has
a definite structure and it performs a definite function.
298
12. Based on the number of
cells what the types of
organisms?
Different living organisms are made up of different number of cells. Based on the number of constituent cells, the organisms
are of two types. Unicellular organism and multi-cellular organism Organisms that are made up of only a single cell are called
unicellular
organism.
A
few
examples
are
Amoeba,
Paramecium and euglena. Organism composed of many cells are called multi-cellular
organisms. For example, plants and animals are made up of millions of cells. A normal adult man has 100 trillion cells
(1014)
299
13. How the size of an organism related with number of cells? The number of cells in an organism is related to the size of the body. As the size of the organism increases, the number of the
cells also increases. Thus, smaller organisms have less number of cells as compared to the larger ones such as elephant and man.
14. Due to small number of cells , small organism face any disadvantages?
The small organism are not in any way at a disadvantage. Their bodies function as efficiently as those of larger organisms. 15. What is the importance of number of cells in an organism?
The increase in the number of cells is attributed to the capability of a cell to divide. After reaching a certain size, the
cells divide into two. The two resultant daughter cells grow and divide again to cause an increase in the size of organisms. 300
16.What is the importance of shape of cells? The cells in multicellular plants and animals have a variety of
shapes. Though these are generally round or spherical, other shapes are also commonly found. These various shapes of the cells are related to the functions performed by them.
17.What is the shape of nerve cell? Draw a diagram of nerve cells.
The nerve cells are a elongated and branched. These are adapted to transmit signals at a faster pace. (fig 8.4 of the text book)
18.What is the shape of muscle cell? Draw a diagram of muscle cells.
Muscle cells are spindle shaped and thin. These features are helps them to contract and relax. (fig 8.4 of the text book) 301
19.What is the shape of skin cell? Draw a diagram of skin cells. Skin cells are flat in shape, which enables them to cover a large
area. 20.Oral cavity is made up of which type of cells? What is its function?
Squamous (thin, flat) cells Inner lining of the mouth or oral cavity is made up of squamous (thin, flat) cells. This perform a protective lining in the mouth.
21. What is the shape of Amoeba? What is pseudopodia? Amoeba as an irregular shape. It forms a projections called
pseudopodia for feeding and locomotion and changes its shape all the time.
302
22. What are columnar cell? Certain organisms are lined by columnar (taller than broad)
cells, which increase their surface area. They also help in secretion, absorption and storage of food. 23. What is the shape of red blood cell? Draw a diagram of
red blood cells. Red blood cells are minute, bioconcave cells to carry
maximum of the oxygen into the body. 24. What is the shape of red blood cell? White blood cells can change their shape which helps, them
to squeeze through the capillary walls. 25. What type of cells plantd have? The plants have thick walled cells (rigid cell wall) which
provide them support and strength. 303
26. If you gently scrape the inner lining of your cheek with the help of a toothpick to take the whitish scraped material on a glass slide and spread it and then put a drop of water and place
a coverslip on it and observe it in the slide under the microscope, What do you observe? Explain with a diagram A large number of cells, which are squamous in shape, are seen.
The inner lining of our cheek consists of squamous cell. These cells can be seen more clearly if stained with a dye, such as
methylene blue. (draw diagram of fig 8.5 (a) 27. What is the average of atypical cell ? The average size of a typical cell is about 0.02 µm in diameter.
The smallest cell of size 0.1 micron or 0.1 µm is PPLO (PleuroPneumonia-like organism) or mycoplasma.
304
28. Which type of cell in human body is the smallest? In human body, the red blood cells are the smallest, with the size
of 7 µm and nerve cell are the longest with the size of 90 µm. 29. What is the size of human egg? Human egg is 100 µm in size.
30. What is the size of egg of ostrich ? The egg of an ostrich measures 170 mm x 130 mm and is the
largest animal cell. 31. What are the shape of muscle cells in animals and fibres in plants ?
Muscle cells in animals and fibres in plants such as Jute and hemp are a few centimetres long. 32. Is the cell egg of a cell is unicellular or multi-cellular?
the egg of a hens are made up of a single cell. 305
33. Is the size of the cell is related with the size of the animal.? Explain. The size of the cell is not related with the size of the animal.
The cells in the body of a whale or an elephant are not necessarily bigger than those in a rat. 34. What are the main part of a typical cell?
A typical cell consists of three main parts: •
Cell membrane,
•
Cytoplasm and
•
Nucleus
306
35. Draw a neat diagram of an animal cell. Diagram of an animal cell
307
36. Draw a neat diagram of an Plant cell. Diagram of an animal cell
308
37. What is cell membrane? What is its function? The cell membrane is a thin delicate and living membrane. It forms the outer boundary of the cell and separates it from the
surroundings and also from other cells. The functions of the cell membrane are:
•
It protects the cell.
•
It gives the shape and rigidity of the cell.
•
It regulates the flow of substances, both in and out of the
cell, for example, glucose and oxygen and carbon dioxide can exit the cells. 38. What is Plasma membrane?
The cell membrane is also called as plasma membrane.
309
39. What is cell wall?
The plant cells have an outer layer, called cell wall, which surrounds the cell membrane. It is made up of cellulose. It is nonliving and rigid layer. It gives a definite shape to the plant cells and
provides support to the plant body as plants are devoid of any skeletal support. The cell wall is absent in animal cells.
40. What is cell wall composed of. The cell wall of plant cell is composed of cellulose. 41. What is the role cellulose in digestive system of human and animals? Human beings cannot digest cellulose because of lack of cellulose
digestive enzymes. Therefore, cellulose acts as roughage in our diet. However, certain animals like ruminants and termites can
digest
cellulose
as
these
have
the
cellulose
digesting
microorganism in their digestive tract. These microorganism have enzymes called cellulose that help in cellulose digestion. 310
42.
How
is
the
onion
membranous
peel
look
like
under
a
microscope? Give some examples of cells which are similar in appearance as onion cell? The onion peel shows a tilled floor like appearance. It is made up of rectangular cells.
Examples :- Tradescantia, Elodea or Rhoeo. 43. Draw a neat diagram of enlarged onion peel cell.
Draw fig 8.7 of the text book
44. Draw a neat diagram of Cytoplasm. Diagram of Cytoplasm
311
45. Describe Cytoplasm and its function. Cytoplasm is basically a jelly like substance that occupies the
space between the cell membrane and the nuclear membrane. It is a watery fluid which contains various compounds such as Carbohydrates, proteins, fats, nucleic acid and mineral salts. Most of the cell functions take place within the cytoplasm. In the cytoplasm, new substances are synthesized, energy is
produced and utilised. The cytoplasm contains several smaller components called cell organelles. Most of these are bounded by a membrane and
perform specific functions. One of the most important cell organelle is the nucleus. The cytoplasm bound by a cell
membrane, along with the nucleus, is termed as protoplasm.
312
46. What is cell organelles? The cytoplasm contains several smaller components called cell
organelles. Most of these are bounded by a membrane and perform specific functions. One of the most important cell organelle is the nucleus.
47. What is protoplasm explain it with a diagram? The cytoplasm bound by a cell membrane, along with the nucleus, is termed as protoplasm.
protoplasm 313
48.Describe Nucleus with the help of adiagram. Nucleus is a small spherical body present in the cell. In a
majority of cells, it lies in the centre. However, in the case of plant cell, it is present at the periphery of the cells. The nucleus, like the brain of animals, is the control centre of the cell. It
directs the growth of the cell and regulates all the activities that occur within the cell. The nucleus consists of the following parts:
•
Nuclear membrane
•
Nucleoplasm
•
Nucleolus
•
Chromosomes
314
49. Describe Nuclear membrane It is thin double membrane structure that nucleoplasm and
separate it from the cytoplasm. It is porous and, thus regulate the movement of the materials in and out of the nucleus. 50. Describe Nucleoplasm
It is the fluid part of the nucleus in which are suspended the nucleus and chromosomes. Like cytoplasm, it is also made up of
a watery fluid in which several compounds are dissolved. It is also known as Kayroplasm. 51. Describe Nucleolus
It is a small, dense, spherical body present within the cell. Nucleolus
manufactures
ribosomes,
which
pass
into
the
cytoplasm and aid in protein synthesis.
315
52. Describe Chromosomes The nucleus contains in network of fibrous materials made up of
DNA and proteins called chromatin. The condensed chromatin forms fibre-like structures chromosomes during cell division. They carry
genes and help in the inheritance of character from the parents to the next generation. In human beings each body cell contains 46 chromosomes.
53. How many chromosomes are there in each cell of a human body? Each
cell
of
human
body
contains
twenty
three
pairs
of
three
pairs
of
chromosome. 54. What are somatic chromosome or autosome? Each
cell
of
human
body
contains
twenty
chromosome. Out of which twenty-two pairs of chromosomes, called somatic chromosome or autosomes, control the characteristic
features and the body functions 316
55. Which chromosome determines that whether the offspring will be male or female?
Each cell of human body contains twenty three pairs of chromosome. Out of which one pair of sex chromosomes decides whether the offspring will be male or female. It is also control the development of the secondary sexual characters that distinguish a male from a female.
56. What is Kayroplasm cytoplasm is also known as Kayroplasm. 57. What is Gene
Genes are the units of inheritance that are present in the chromosomes. They pass on the hereditary characters from
parents to their offspring. Different combination of the genes are responsible for the different characteristics that each one of us posses. 317
58. What are the types of cells based on the organisation of the
nuclear region (nucleus)? Based on the organisation of the nuclear region (nucleus) the cell can be categorised into two types, that is Eukaryotic cells
and prokaryotic cell. 59. What is the meaning of Eukaryotic? Describe Eukaryotic cell. Give some examples of Eukaryotic cell.
The meaning of Eukaryotic is true nucleus, that is eu= true, karyon= nucleus.
Eukaryotic cell are the cells which have a well-organized nuclear region with a distinct nuclear membrane. The organisms composed of such cells are called eukaryotes.
A few examples of Eukaryotic cells are the cells of plants and animals. 318
60. What is the meaning of Prokaryotic? Describe Prokaryotic cells. Give some examples of Prokaryotic cells. The meaning of Prokaryotic is primitive nucleus, Pro= primitive, karyon= nucleus.
Prokaryotic cells do not have a well organised nucleus. The nucleus region is not surrounded by nuclear membrane and, thus is in direct contact with the cytoplasm. The organism processes the cell are called prokaryotes. A few example of these are bacteria and blue green algae.
61. What are the other prominent cell organelles present in the cytoplasm of eukaryotes, besides the nucleus.
There are many other cell organelles present in the cytoplasm of eukaryotes most prominent of these are : •
Mitochondria,
•
Vacuoles and
•
Plastids. 319
62. Describe Mitochondria. Why Mitochondria called powerhouse of the cell?
These are small, spherical or rod-shaped organelles scattered in the cytoplasm of all the eukaryotic cells (all the animal and plant cells). These contains large number of enzymes that
oxidise food molecules during respiration and provide energy to the body. Therefore, these are called powerhouse of the cell.
63. What are Vacuoles? These are the sac-like structures, bounded by a membrane. As compared to the animal cells, which have very small vacuoles,
plant cells are very large vacuoles filled with watery fluid that contains many dissolved substances. In Amoeba, a few small vacuoles contain food particles and are known as food vacuoles.
320
64. What are Plastids? Plant cells contain special organelles that contain pigments of
different colours. These are called plastids and are the largest organelles in the plant cell. Plastids are absent in animal cells.
65. What are the types of plastids,based on their colour? Based on their colour, these are of the following types : •
Leucoplast: These are the colourless plastids which contains
starch, for example potato has lots of leucoplasts. •
Chromoplasts:
These plastids are yellow, orange or red in
colour. They provide colour in the flowers and fruits and vegetables like tomato and carrot. •
Chloroplasts: These are green in colour as they contain the green pigment chlorophyll present in green plant parts of a plant. You have studied in the previous class that chlorophyll
helps
in
the
photosynthesis.
manufacture
of
food
by
the
process
of 321
66. What are the function of following Cell organelles?
Golgi bodies , Endoplasmic reticulum, Ribosomes , Lysosomes, Centrosomes. Cell organelles and their functions. Cell organelles
function
Golgi bodies
Secrete substances.
Endoplasmic reticulum
Make transport system.
Ribosomes
Responsible for protein synthesis
Lysosomes
Destroy old body cells, and foreign bodies
Centrosomes
Control cell division, present only in animal cells.
322
67. Draw the diagram of sections of leaf, steam, stomach and kidney. Section of leaf.
323
Section of steam.
324
Section of stomach.
325
Section of Kidney
326
68. Though the cells differ in size and shape , how is it possible to make the existence of an individual possible?
All types of cells have almost common organelles. Therefore, although the cells differ in size and shape, they are similar in their fine structure. Difference in shape, size and various
combinations of the cells helps in carrying out different function. For performing these functions, cells join together to
form tissues. The tissues join to form organs. A set of organs together constitute the organ system such as a digestive system and the respiratory system. All these systems work in
coordination to make the existence of an individual possible.
327
69. Compare between plant and animal cells. Difference between Plant cell and Animal cell S.No 1
Plant Cell
Animal cell
Cells wall composed of cellulose, is Cell wall is absent
present outside the cell membrane 2
Chloroplast pigments
containing
and
other
chlorophyll Plastids are absent
plastids,
are
present in the cytoplasm. 3
it has one or two large vecuoles filled Vacuoles with watery fluid
4
are
extremely
small or absent
Centrosome that helps in cell division Centrosomes is present is absent
5
The Stored food material is starch
The Stored food material is glycogen
6
Nucleus is present at the Periphery of Nucleus the cell
is
the
centrally
located in most of the cells 328
70. Describe cell division and growth, with the help of a nest
diagram. Give some examples of cell division. Animals and plants are multicellular organisms, consisting of a large number of cells. All these cells arise from a single cell
called fertilized egg or zygote. It divides repeatedly and produces a large number of cells by the process of cell division
and, thus, a multicellular organism develops. The cell division is always
followed by the growth of the cell, where the size of
the cell doubles before the cell division again. This is how all animals and plants
grow. 329
Some cells of the body keep on dividing throughout life, for example each second, about 30 lakh blood cells die and are
replaced by new blood cells. The cells of the skin keep on the dividing throughout the life replacing the cells that are almost from the surface. Moreover, they help in the healings of wounds and injurious. 71. Why nerve cell cannot be replaced after a certain age?
The nerve cell of the brain can not divide and, thus, cannot be replaced after a certain age.
330
Back to contents 331
What is non-uniform motion? The motion of a body becomes non-uniform when either its speed or is direction changes and this keeps on happening very
often. When does our bicycle start moving faster?
The bicycle start moving faster when the cyclist put in “effort” by pedalling faster. When does a bullock cart move faster?
bullock cart move faster when the bullock
pushing the cart
harder.
When does a moving car slowdown on stop? Moving car slowdown on when the driver applying the brakes. What is effort?
The effort is usually in the form of ‘push’ or ‘pull’. We use the use the term ‘Force’ for it. 332
What is the cause behind a non-uniform motion? It is always the action of one or the other force that makes a
body move with a non-uniform motion, that is, makes it change either its speed or its direction of motion. The speed of an object increases if the force is applied in the direction of its
motion. The speed decreases when the force is applied opposite to the direction of its motion. How the strength of a force is represented?
The strength of a force is represented by its magnitude. Is the force have any direction?
It is needed to specify the direction of force. The force can be changed by either changing its direction or magnitude of both.
333
What is meant by applying force? Give some examples of force applied.
Applying force means make an effort to push or pull a body. Pushing or pulling harder only means exerting a greater force. We can have many
examples of a push or a pull from our daily life. A door can be opened or closed by a push or a pull. For pushing or pulling a heavy Iron door, we usually have to apply greater force than that needed for a wooden door. What are the Effects of force? •
A Force can produce motion.
•
A force may only tend to produce motion.
•
A force can stop motion.
•
A force may only tends to stop motion.
•
A force may speed up or slow down a moving object.
•
A force can also change the direction of motion of a body.
•
A force can change the shape of an object.
•
A force can change the size of an object.
334
Give an example that a force can produce motion. Small box, fitted with wheels, is lying in one corner of a room it needs to be move to another corner of the Room. We pull its strap and move it to the desired corner.
Give an example that a force may only tend to produce motion. While going to school, Varun finds a heavy stone lying on the road. He pushes hard at it but does not succeed in moving it. Here, the force applied by him could not produce any motion but only tended to do so.
Give an example that a force can stop motion. Ritesh is slowly riding his bicycle. His friends Sachin pulls at its
carrier. The bicycle comes to rest. Thus a force can stop motion. Give an example that a force may only tends to stop motion. If the bicycle is moving fast, the force applied may not succeed in
stopping motion but may only slow it down. Thus, in some cases a force may only tends to stop motion. 335
Give an example that a force may speed up or slow down a moving object. Gautam sees a labourer pulling a cart on the road. He plans some mischief and start pulling the cart backward. The cart slows down
and the labourer feels unhappy. Now, Gautam start pushing the cart forward. Cart starts moving faster when the labourer feels happy. When the speed of motion is changed? When the force is applied on an object in the direction of motion, its speed increases. However, if the force is applied on the object in the
direction opposite to the direction of motion, its speed decreases Give an example that a force can also change the direction of motion
of a body. A bowler of an opponent team delivers a fast ball directed at the Wicket. The batsman hits it with his bat and sends it racing towards
the boundary. The batsman’s hit produces a force that changes the direction of motion of the ball. 336
What is state of motion?
A change in either the speed of an object or its direction of motion or both of this, is described as a change in the state of motion of the object. The state of motion of an object can be
described by its speed and direction whereas the state of rest is described by a state of zero speed.
Give an example that a force can change the shape of an object. Take a lump of moulding clay and press it to make various toys. Here, a little effort helps us to mould the clay into various
variety of shapes. Give an example that a force can change the size of an object. Take a rubber band and stretch it. It gets elongated. Similarly, a
spring when stretched gets elongated. It becomes shorter when compressed. 337
Define force. What is the SI unit of force? A force is a push or a pull which produces or tends to produce, stops or
tends to stop, motion. It may also change the speed or the direction of motion or the shape and/or size of a body. The SI unit of force is newton (N).
Explain are balanced and unbalanced forces? If two forces acting on an object in the same direction, the net force as
acting on the object is equal to the sum of the two forces. On the other hand, if the two forces are acting in opposite direction, then the net force acting on the object is equal to the difference between the two forces. If two equal forces act on a stationary object, the difference is zero. So, the object does not move. Here, the two forces balance each other and the net force is zero. These forces are called balanced forces. If two unequal forces act on stationary object, then the object starts moving in the direction of
the larger force. However, the difference between the between the two forces should be sufficient enough to move the object. Here, the net force is
in the direction of the larger force and is called an unbalanced force. 338
Mention the effect of the force associated with the following
event A goalkeeper hitting at the football.
A Hockey player intercepting a ball in a match A wicket keeper catching the ball snicked by a batsman. A batsman hitting a ball for a six.
A footballer giving a sidewise kick to a ball. An iron smith hammering a piece of red hot iron. A Lady using a rolling pin to roll out dough for making chapattis.
A girl squeezing toothpaste from a tube. Aa person squeezing a lemon on his salad.
A man suspending a gas cylinder from a weighing spring
339
Event A goalkeeper hitting at the football –
Effect of the force Force can produce motion
A Hockey player intercepting a ball in Force can stop the motion a match A wicket keeper catching the ball Force can stop the motion snicked by a batsman.
A batsman hitting a ball for a six.
A force can also change the direction of motion of a body
A footballer giving a sidewise kick to A force can also change the a ball. direction of motion of a body An iron smith hammering a piece of A force can change the shape of red hot iron. an object. A girl squeezing toothpaste from a A force can change the size of an tube. object. A Lady using a rolling pin to roll out A force can change the shape of dough for making chapattis. an object. A person squeezing a lemon on his A force can change the size of an salad. object. A man suspending a gas cylinder from Balance force. a weighing spring 340
What are the types of forces?
Types of forces•
Muscular force
•
Impact force
•
Force of friction
•
Force of gravity
•
Force of gravitation
•
Electrical Force
•
Magnetic force
•
Contact and non-contact forces
341
Define muscular force?
The force applied by the muscle of our body is termed the muscular force. Give an example of muscular force.
Ram has a beautiful well-mown grassy lawn. Every Sunday he cuts its grass with a lawn-mower. It takes him half an hour to complete the
mowing and he feels dead tired. For pushing the lawnmower, he has to apply force. This force is applied by the muscles of his arms, which get tired after work. Define Impact force The force produced by the impact of an object, on another, is the
impact force Give an example of impact force.
At a inter class cricket match, Varun delivered a real fast ball that uprooted the wicket. Here, the impact of the fast moving ball succeed in uprooting the wicket. 342
Give an example of force of friction.
Roll a ball on the rough road outside your house it stops after moving across a short distance. Now, roll it on the smooth floor of a room. It moves through a much longer distance before its stop. The moving ball stops because of the existence of a force due to the roughness of the floor. This force acts between any two surfaces in
contact and tries to opposite the motion. It is more between two rough surfaces and less between two smooth one.
Define force of friction. The force acting between any two surfaces in contact and tending to oppose motion is called force of friction.
Why when all objects are dropped falls freely towards the ground? A stone or an apple, when released from a certain height, falls
freely towards the ground this is because of the force of gravity exerted by the earth on all objects on or near its surface. 343
Explain an activity to show the force of friction. A sheet having a rough surface is taken and kept on top of a table. Also, a rectangular wooden block is taken and a nail is
fixed on one of its sides and with it a long thread is attached. The block is placed on the rough surface of the sheet; the thread
is taken down the table and a small weight attach is attached to its free end. It is observed that the block does not move. This is because of the force of friction between the block and the rough
surface of the sheet. The block will move only by attaching a sufficiently large weight to the free end of the string.
Define force of gravitation A force of attraction is exist between any two masses in the universe. This is a universal and is known as a the force of
gravitation. 344
What are the effects of force of gravitation? The force of gravitation keeps the planets moving around the
sun and moon orbiting around the earth. Even the tides in the sea are caused by the gravitational force between earth and the moon.
Define electrical force. The force exerted by an electrically charged body is termed as
the electrical force. Give an example of electrical force. If we comb our dry hair vigorously and then bring the comb near
tiny bits of paper, we observed that they are drawn towards the comb. Vigorous rubbing makes the dry comb electrically charged. Due to the presence of this charge the comb attracts
tiny bits of paper. 345
Explain an activity to show that oppositely charged object
attract each other while similarly charged object repel each other. A Pitch ball is taken and suspend it by using a cotton thread,
from a stand. A glass rod is taken and it is vigorously rubbed on a piece of silk and then quickly these rubbed glass rod is
brought near to (but not touching) the pitch ball. It is observed that the pitch ball gets attracted toward the glass rod, however, if it comes in contact with glass rod, it (immediately) get
repelled. Initial attraction of the pitch ball is due to the force of attraction between oppositely charged object. Its subsequent repulsion, after coming in contact with (rubbed) glass rod is due
to the electrical force of repulsion between similarly charged object. 346
Define magnetic force. The force associated with the magnet is called the magnetic force.
Give an example of magnetic force. A magnet and attracts iron nail, pins and other iron objects. It can also attract or repel another management.
Explain an activity to show to separate a mixture of iron feelings and sand.
A mixture of sand and some finely powder iron filing are taken and the mixture is spread on a sheet of paper. A strong bar magnet is held and one of its end is moved rapidly through this mixture. The filling clung to the magnet’s end are put on a separate sheet of paper. This process is repeated a few times. And thus it is possible
to separate out the iron feeling, from the sand , in the mixture. We make use of the magnetic force, between the strong bar magnet,
and the iron feelings, to carry out this separation. 347
Define contact and non-contact forces. •
The forces come into play only when the two objects are in contact with each other are called contact forces.
•
Some forces seen to act even when there is no direct contact between the two objects, these forces are called non-contact
forces . Give some examples of contact forces.
A batsman hit a ball a horse pull cart. Which type of forces are categorised as contact force?
Muscular forces, impact forces and frictional forces are contact forces. They come into play only when two objects are in direct
contact with each other. What is nuclear forces. The forces almost disappear when the same particles are outside the nucleus are called nuclear forces. 348
Give some examples of non contact forces.
A magnet attract or repel another magnet even from a distance. A charged ebonite rod attract or repel another charged rod even from a distance. What are the forces categorised as non contact forces? The gravitational , electric and magnetic forces are known to be non contact forces. What are the different types of forces seen on nature? Explain. are the
different types of forces seen on nature can be explained through mainly
four types of forces. These forces are - Gravitational force,
Electromagnetic (electrical and magnetic) force, Weak force and Strong force.
Most of the forces that come into play in our daily life situations are electromagnetic in nature. For very large or astronomical objects, the gravitational forces are the most important ones. The weak and strong forces are important mainly within the nuclei (the very tiny central core) of atoms. 349
Explain an activity with a drawing to show that compression of a
spring increases as the compressing force increases. Give an example where this principle is used. On strong spring like the one used in a sofa set is taken and its
height from the floor is measured. It is, say, about 15 cm. One brick is placed on the spring and it is observed
that the spring gets
compressed. The height is measured again. It is found to be , say, about 14 cm. This shows that the length of the spring has decreased by (about) 1 cm. Now, one more brick is placed on the spring and difference in the compression of the spring is observed and it is found that the decrease in the length (or compression) of
the
spring
is
(about)
length(compression)
2
caused
cm by
this two
time.
The
bricks
is
decrease double
in the
compression produced by one brick. From this, it is seen that compression of a spring increases as the compressing force increases. 350
This principle holds for the extension of a spring ‘hooked’ at its upper end and having a weight suspended at its lower end. This implies that a spring can be used for the measurement of forces.
It is this idea that is used in designing a spring balance. We use a spring balance for measuring weights. He was the inventor of the spring balance.
Who is the inventor of the spring balance? Robert Hooke discovered that the extent to which an elastic
body stretches out of shape is in direct proportion to the force acting on it. He was the inventor of the spring balance. 351
Explain an activity to show that the extension of the spring is due to the force of gravity acting on the masses. A spring about 10 cm long with its two ends twisted into hooks is
suspended in the wall or in a wooden frame from a peg fixed on the wall. A pan from the hook is
also suspended at the lower end of the spring. A needle about 6 to 7
cm long is fixed at the lower end of the spring. A paper strip is pasted on the wall behind the
spring as shown in the figure.
352
When there is no weight placed on the pan, the position of the needle
on the paper strip as is marked zero. Now a weight of 10 g is added. It is observed that the needle moves downward. its new position as 10. By go on adding weights of 10 g and every time marked the corresponding position of the needle as 20, 30, 40, 50 etc the spring balance is now ready for use. Here the extension of the spring is due to the force of gravity acting on the masses of 10 g , 20 g , 30 g etc. The calibrated scale can then be used to measure weights.
Describe a laboratory spring balance. Spring balance
consists of a spring fixed
inside a metal case. The front has a brass sheet with a slit in it. A scale is etched on this brass sheet near this slit. The pointer moves through the slit on this scale. The position of a pointer on a scale indicates the
Fig 11.15 :
force applied at the hook attached to the
Spring
lower end of the spring.
Balance 353
To use a spring balance for measuring the weight of a given object,
the spring balance (by its hook) is to be suspended from a suitable support. The object to be weighed is attached at its lower end. The pointer of the spring balance comes to rest after a short while. The
position indicates the weight of the suspended object. Define friction
It is a force that is always present between any two surfaces in contact and it opposes the motion. Give some example of friction and explain it. A ball rolling down the floor and then stopped after moving some distance is an example of friction.
When the movement of a ball
rolled down on a floor is observed it is
found that it moves for a
while, slow down, and then stops. It is a force that speeds up or
slows down an object.
Therefore, the ball rolling down the floor
must have experienced a force that opposed its motion. This force is the force of friction. 354
What are the factors that affects friction? •
It is an opposing force that always opposes the motion between any two surfaces in contact.
•
It depends on the smoothness as well as a nature of the surface in contact.
Give an example to show that the force of friction depends on the smoothness as well as a nature of the surface in contact The force of friction always opposes motion but is magnitude is not always the same. If two similar rubber balls are thrown with equal force, one on a rough road and the other on a smooth cemented floor. The rubber ball rolling on the rough road stops earlier than the one rolling on the smooth floor. This is because opposite force of friction on the rough road is greater than that of the cemented floor. Thus, the force of friction depends on the smoothness of a surface in contact.
If this experiment is repeated with a metal ball instead of a rubber ball. We find that the metal ball rolls over long distances than a rubber ball on each of
the surfaces. (of course, in this case also, the metal ball rolling on the rough surface stops earlier), We observe here that a force of friction also depends on
the nature of the surfaces in contact. 355
Explain friction can be regarded as the force arising from interlocking of irregularities on the surface of the bodies in
contact. A saw is used by a carpenter. When the teeth of two such saws
get interlocked, it becomes very difficult to slide one over the other. An object or a surface may appear smooth to naked eye but,
when
seen
through
a
microscope,
it
shows
many
irregularities. Even the smooth edge of a blade may look somewhat like a saw so when seen through a powerful microscope. These irregularities in the surface of the bodies
get interlocked, like the saw teeth and the relative motion between them is made difficult. The rougher the surface, the
greater are the irregularities. The opposing force, of friction, is always greater in such a case. 356
What are the types of friction?
We can classify friction on the basis of the relative motion between bodies. •
Static friction - when two non moving bodies are in contact
with each other, the friction present between them is called static friction. Static friction has to overcome before the bodies can move.
•
Kinetic or dynamic friction - when a body starts moving over a surface, the friction between it and the surface is known as
a Kinetic or dynamic friction. •
Sliding friction - The friction produces due to the sliding is called sliding friction.
•
Rolling friction - The fiction that which arise in when the body rolls over a surface is called rolling friction. 357
Explain why is it easier to roll a given object than to slide it. Suppose, we have a box full of cloths. If we try to slide it from
one corner of the room to another, we find it quite difficult and tiring. This is because we need quite a large force to slide the object. The friction, produces here due to the sliding is called
sliding friction. Now, a box that is fitted with wheels is taken, it is quite easy, even for a child to move the box even though it is
full of close from one place to another. This is because the fiction that now comes into play is rolling friction which arise in the body rolls over a surface. It is observed that under
identical conditions, rolling friction is much less than the sliding friction. Therefore, it is easier to roll a given object that to slide it.
358
What are the methods used to reduce or minimise friction? To reduce or minimise friction following methods are used : •
Smoothening of the surfaces.
•
Replacing sliding friction with rolling friction.
•
Oiling or lubricating the moving parts of the machines.
•
Use ball bearings.
•
Streamline the shapes of moving bodies.
Define lubricants
lubricants are defined as those substances which reduces friction. Why we oil or lubricate the moving parts of the machines?
When we oil or lubricate the moving parts of the machines, a thin film of the oil or the lubricants comes in between the
layers in contact. This reduces the friction between them considerably 359
What are the ball and roller bearing? Where are they used and why? Ball bearings or roller bearings consists of small balls or rollers
made of steel. These are places between the moving surfaces and use of this bearings reduces the friction to 1/20th or 1/30th
of its original value. What is streamline shapes, what are its benefit. It have been observed that racing cars and aeroplanes have
specially designed bodies. These type of shapes are called streamline shape. Nature, too, has blessed that fast moving animals such as the cheetah and fish with streamlined bodies.
These special shapes helps in reducing the friction produced by air or water, called drag, when they move through them.
360
What is drag on which factors drag depends? The friction produced by air or water, called drag. The frictional
force or drag experienced by an object when moving through air or water , commonly called fluids, depends on the speed and
shape of the object and on the nature of the fluid as well. Why friction regarded it as a curse Or
What are the harmful effects of friction •
Friction also produces heat - the heat produced due to friction
provides quite problematic. A rapidly
operating machine
produces a lot of heat which results in a lot of energy. The heat so produced can also damage the machine. To prevent
this, we employ various methods to reduce friction. •
Friction between the two surfaces causes their wear and tear. 361
Why we often say friction as boon or a necessary evil? It may appear that since the force of friction always opposes the motion, it is always a curse. This is not so, because very often the force of friction is always a boon or, as we often say, a necessary evil. In fact life would have been almost impossible if there were no fiction. Friction help us to work and to drive for vehicles. It is also helped us to produce heat.
Explain an two activities to show that friction between the two surfaces causes their wear and tear.
(i) A cardboard or a plyboard is taken and when it is rubbed with a piece of sandpaper vigorously it is observed that tiny filings on the plyboard
start falling on and around the board. Thus, it may concluded that friction between the two surfaces causes their wear and tear. (ii) A pencil is taken and some words or sentences are written on a paper. When an eraser is used to erase these words written by the pencil it is observed that as the written words get erased , tiny filings of
the eraser fall on the paper. Thus, it may concluded that friction between the two surfaces causes their wear and tear. 362
Write some of the benefits of friction?
•
Friction helps our feet to grip the road and unable us too walk.
•
The trades on the tyres increase friction and provide them with a better grip on the road
•
While applying brakes to our bicycle or vehicles the resulting fiction stops the movement of the wheels
•
When a matchstick struck against the rough surface of the matchbox, we use friction to produce heat and thus, to light the matchstick.
How friction helps our feet to grip the road and unable us too walk? In an effort to walk, we push the earth backward. In return, the
earth pushes us forward and we are able to walk. On a highly polished floors, there is very little grip between the floor and our
shoes due to lack of frictions. Hence on a polished floor the moment we try to push the earth backward, we slip and fall. So it is the friction that helps our feet to grip the road and unable us too walk 363
Why corrugations are made on the soles of our shoes?
corrugations are made on the soles of our shoes to increase friction between feet and the ground and help us to have a better grip on the road.
Why trades are made on the tyres of the wheel of the vehicles? New tyres all vehicles have many trades or corrugations on them. The trades on the tyres increase
friction and provide
them with a better grip on the road. When the treads of a tyre loses its grip on the road and the vehicles tends to skid.
How friction is used to stop motion of a bicycle. while applying brakes to our bicycle friction is used. When we apply brakes to our bicycle, we are actually clamping rubber
blocks against revolving rim of the wheel. The resulting fiction stops the movement of the wheels. 364
Why trolley wheels have rubber washers.
Sometimes, we also use different material to increase friction. For example, trolley wheels have rubber washers. Why a wet glass slip more easily from our hands than a dry
one? How slipping is prevented? Wet surfaces generally reduces friction. A wet glass tends to slip more easily from our hands than a dry one. Therefore,
friction can be increased by making the service dry. Why when any object starts slipping from our hand we hold it
more firmly? We can increase the grip by increasing the pressure on the surfaces on contact. Thus when any object starts slipping
from our hand, we hold it more firmly. This results in an increase of friction between the object and our hand. 365
Back to contents 366
1. Explain how the effect of force is depends on the area on which it acts ?
Effect of a force depends on the area on which it acts.This can be explained with help of follwing example. Consider an example of a girl walking on a soft ground the
force pressing the ground downwards is the weight of the girl. However,
the depth of her feet impression on the ground
increases when she uses shoes with pointed heels compared
to the impression produced by flat-heeled shoes. Clearly, it is the decrease in the area of contact of her feet
with the ground and that has contributed to an increase in the depth of impression of her feet. Thus, it appears that, the effect of a force increases with the decrease in the area.
367
2. Why it is more difficult to fix a blunt nail than a sharp nail? It is more difficult to fix a blunt nail than a sharp nail because of
the sharper the nail, the smaller is its area of contact with the wood and, therefore, the greater is the effect of a given force on
it. 3. Why it is easier to cut fruits and vegetables with a sharp knife than with a blunt one?
it is easier to cut fruits and vegetables with a sharp knife than with a blunt one because the sharper end has a smaller contact
area than the blunt end. 4. Why school bags have wide shoulder straps. School bags have wide shoulder straps because broad straps
increases the surface area on which the force is acting and thereby reducing the pressure on the shoulder of the student who is carrying the bag. 368
5. Write the factors on which effect of given force depends? The effect on which effect of a given force depends are-
•
magnitude of the given force and
•
the area over which the force acts.
6. Define pressure and write its formula. Pressure is defined as the ratio of
the force, acting
perpendicular to the area, and the area on which it acts.
Formula for finding pressure – Pressure =
7. What are the units of pressure? The unit of pressure are kgwt/metre2 or Newton/ metre2.
8. What is the SI unit of pressure? The SI unit of pressure Newton/ metre2. 369
9. What is the name of the SI unit of pressure? What is its abbreviation?
The name of the SI unit of pressure is pascal. It is abbreviated as Pa.
10. Define one pascal. The pressure, at a given surface, equals one pascal when a force of one Newton acts perpendicularly to 1 square metre
area of that surface. That is : 1 Pascal = 1 Newton per square metre (
)
11. Establish a relation between kgwt/ m2 and Pascal Since 1 kg wt = 9.8 Newton, We have
1 kgwt/ m2 = 9.8
= 9.8 pascal
370
12. Give an example where the idea pressure is used by nature? Or
Why the elephants have broad feet? The broad feet of the elephant increase the area of its contact
with the ground. This reduces the pressure of its weight on the earth and the feet do not sink too much in the ground. 13. Why Buses and trucks generally have double wheels at the
back? Buses and trucks generally have double wheels at the back.
which increases their area over which their weight acts and hence, reduces their pressure on the ground. 14. Why heavy duty tractor have broad iron belts?
Heavy duty tractor have broad iron belts which increases their area over which their weight acts and hence, reduces their pressure on the ground. 371
15. Why the foundations of buildings and dams are made broader? The foundations of buildings and dams are made broader. This
makes their overall weight act over a larger area and reduces their pressure on the ground. 16. Why it is easier to glide on snow on a pair of skies than walk across as such one’s shoes? The use of skis increases area over which is the weight of the
man acts. Therefore, his pressure on the snow decreases and he can glide across without sinking deep into the snow. 17. Why needles are made pointed and why nails have a sharp
end? When we apply some force a pointed needle or a sharp nail, the
resulting pressure becomes quite large this is because the pointed needle or the sharp ended nail to penetrate into the cloth or wall respectively. 372
18.Why a gas balloon often bust if too much air is blown into it? This is because of the increase in the pressure of air over the
thin membrane that comprises the surface of the balloon. This membrane bust when the pressure on the air inside it exceeds a certain limit.
19. Why a bicycle tube feel hard ,when air pumps it? When air is pumped into a bicycle tube that air exerts pressure
into the bicycle tube. As a results the tube gets inflated and it feel hard . 20. In which direction gases exert pressure on a open or closed
container? All gases exert pressure on the button, the walls and the top (if present) on their container.
373
21. What is the atmospheric pressure? Explain it. The pressure due to the air in the atmosphere is called atmospheric
pressure. The vast mass Atmospheric pressure of air extends up to a height of about 200 Km which has weight. The weight of this huge column of air exerts a pressure . This weight of air acting per unit area is known as the pressure of the atmosphere or atmospheric pressure.
22. What is barometer ? Who invented it? Barometer
is
an
instrument
used
for
measuring
atmospheric
pressure. It was invented in 1643 by Evangelista Torricelli. 23. What is the liquid used in barometer invented by Evangelista Torricelli ?
Evangelista To used a column of water to make his barometer. Latter on by which liquid the column of water is replaced in
barometer? Later, water column of the barometer was replaced with pure mercury.
374
With a neat diagram describe the construction and working
principle of a mercurial barometer. The mercurial barometer consists of a long glass tube filled with Mercury.
The open end of the tube is inverted in a small cup of mercury called cistern. The
air
exerts
pressure
on
the
mercury in cistern and it is able to hold mercury to a certain level of the
column. The increase in air pressure increases the level of mercury in the column and decrease in air pressure
decreases the level of mercury in the column. In this away the pressure is
measure by looking at the rise and fall of mercury.
375
Who is Otto Von Guericke ? Describe his experiment about the atmospheric pressure?
In the seventh century, a German scientist by the name of Otto Von Guericke performed an interesting experiment to show how large is atmospheric pressure.
Experiment- Two hollow hemispherical vessels of identical size were fitted into each other. The two hemisphere were tight fitting and become air tight when join together. A vacuum pump
was used to evacuate the air present inside it them. It was found that two teams of eight horses each, pulling the two
hemispheres in opposite directions, were needed to separate them. It was atmospheric pressure acting from outside that was keeping the two hemispheres pressed against each other.
376
In what unit atmospheric pressure is usually expressed? Atmospheric pressure is usually expressed in ‘millimetres of
mercury’. abbreviated as ‘mm mercury’. What is the normal atmospheric pressure? The normal atmospheric pressure, at the sea level, is 760 mm of mercury. Take a small glass tumbler, water and a sheet of cardboard.
First fill the glass tumbler right up to the top with water. Place a sheet of cardboard on it. Press it well with the hand and invert it quickly and carefully, taking care that there are no air bubbles
in between the water and the cardboard what do you observe? Explain the reason behind it?
It is observed that the water in the tumbler does not spill. This is because the weight of the water in the tumbler is supported by the pressure of the atmosphere acting from below. 377
Take a tin can with a tight-fitting stopper.
First, pour little
water into the tin can and heat it over a burner. Keep on heating until steam start forming so that it dries out most of
the air from the tin can. Remove the tin can from the burner and fit the stopper at its mouth tightly. What happens to the
tin can after sometime? After sometime, the tin can get crushed. When cooled, the steam inside the tin can condensed. Now there is nothing
inside the tin can to balance the outside atmospheric pressure. Therefore, the atmospheric pressure, acting on from outside, crushes the tin can. Thus, air exerts pressure.
378
After sometime, the tin can get crushed. When cooled, the steam inside the tin can condensed. Now there is nothing inside the tin can to balance
the
outside
atmospheric
pressure.
Therefore, the atmospheric pressure, acting on
from outside, crushes the tin can. Thus, air exerts pressure. Warning - Do this activity only under the supervision of your teacher/parents.
379
We find it very difficult to push down on the empty inverted glass bottle or any other such container into a tank filled with
water, Why? The pressure exerted by the water opposes the downward movement of the air present in the container and thus resists it
when it is pushed down. When we tilt this container and let water flow into it, it becomes a very easy to lower the container into the tank.
How much force is exerted by the atmosphere on all human beings and animals on the earth?
The atmosphere exerts a force equal to the weight of about 100 persons on each square metre at sea level.
380
How does human body withstand atmospheric pressure? Why do
they do not get crushed under this pressure? Human beings and animals do not feel any discomfort because their bodies get a accustomed to this to this pressure. Human
beings and animals develop and internal pressure that balances atmospheric pressure and this prevents from and prevents them
from getting crushed. This internal pressure is provided by the fluids present within our body cells. When people normal living in plains, go to high mountains, quite
often they find blood oozing out from their nose, Why? Their internal pressure, which was conditioned to balance the atmospheric pressure in plains now finds a reduced pressure (on
the high mountains) opposing it and the excess pressure inside causes the blood to ooze out. 381
Why astronauts wear specially made suits to go into space? Astronauts wear specially made suits to go into space where
the
external
pressure
is
much
lower
than
the
normal
atmospheric pressure. Their special suits maintain a pressure between the suit and the body which is equal to the atmospheric pressure in space. This prevents the body cells from bursting under the (high) internal pressure within the
human body. Why deep sea divers need special protective suits ? Human body is capable of withstanding pressure up to 40 m in
deep water. Therefore deep sea divers need special protective suits to protect themselves from excessive pressure at
greater depth. Of course, the bodies of deep sea animals are tuned to this type of excessive pressure and they can stay in deep seas without discomfort. 382
Give three examples of role of atmospheric pressure in our day to day life.
Examples of make use of air pressure in our day to day life are given below : •
While having it cold drink, when we suck it through a straw, we take out some air present in. This lowers the pressure of the air therefore the outside air then pushes the cold drink
into our mouth through the straw. •
While filling a medicine dropper or a fountain pain, we push out the air in it by pressing the rubber cap or the rubber
tube. This reduces the pressure inside the tube. Now, the higher pressure of the air outside
again
pushes the medicine
or the ink into the dropper or the fountain pain. The doctors also use the same principle when they will fill their syringe with medicine for injection purposes. 383
•
A vacuum cleaner is a device used for removing dust and paper pieces quickly and effectively from homes and offices. Here the air inside a collecting bag it sucked out
by electric motor. The outside air then rushes into the bag, taking along the dust and paper pieces present on
its way. In which directions liquids exerts pressure on the walls of the containers they are poured into?
Liquids exert pressure at the bottom , the walls and the top (if present) of the container they are poured into. The container can be open vessel or a closed vessel.
384
Fix a Rubber Balloon at the lower end of an open glass tube. Pour some water into it and observe the Balloon. Now, pour some more water into the tube and again observe the balloon. What happens to the balloon? Explain with a neat sketch. It is observe that the balloon starts bulging outwards as water
is poured into the tube. The bulge increases with an increase in the height of the liquid column. This shows that the liquid column exerts a pressure on the bottom. This pressure
increases with an increase in the height of the liquid column.
385
Take two identical thin glass tubes and close their one in which two identical balloons. Now pour a certain amount of water in one in one of the tubes and an equal amount of glycerine in
other tube. What happens to the balloon? Explain with a neat sketch. The balloon at the end of the tube filled with the glycerine
bulges out more than that at the end of the tube filled with the water.
This shows that the pressure of a liquid depends on its density. It is more for a denser liquid then for a lighter liquid.
386
Show an experiment, with the help of neat sketch , that the pressure remains the same in all direction at a given depth. Material requires- U-tube manometer, a thistle funnel, a rubber tube, a tall vessel or a beaker and some water.
Procedure - (figure 12.22) Cover the mouth of the thistle funnel with the rubber sheet. Connect it to the manometer by using a rubber tube. Now immerse the funnel into the tall vessel containing water. Keeping the funnel at a particular depth, change its position so that is mouth is directed downwards, upwards and sideways in turn. Care
to be taken that the depth of the centre of the rubber sheet does not change.
Observation- The manometer reading in all the position of the funnel (for which the centre of the rubber sheet will is at same depth) , the manometer reading does not change.
Conclusion- This shows that the pressure remains the same in all direction at a given depth 387
Take two plastic containers. In one container, make three holes at different heights and into other, make three holes at
same height. Now. keep both the container under a tap and let the water flow out through the holes. What do you observe? Explain with a neat sketch. It will ne observed that from the container A, water from the lowest hole come out with the greatest force and falls at the
maximum distance from the base, while water from the highest hole falls at the minimum distance from the base on the other hand, in container B water comes out from all the holes with
the same force and falls at the same distance from the base. This shows that water or any liquid exert pressure on the sides
of the container and this pressure increases with increasing depth. On the other hand, at the same height, pressure is same in all the directions. 388
Write the properties of the pressure of a liquid in an open vessel. •
The pressure of a liquid column increases with an increase in
its density. •
Liquids exert pressure on the bottom as well as the sides of the container.
•
The pressure of a liquid, at a given depth, is the same in all the directions.
•
The pressure of a liquid column current increase with an increase in its depth.
In which direction the liquid in closed vaseel exerts pressure?
We know that liquids do not have no shape of their own. Hence, when a liquid is present in a closed vessel and is pressed at one point, it spreads out equally in all possible directions. The
following simple experiments demonstrate this property of liquids. 389
Take a tube fitted with a piston. fill it with coloured water and attached a rubber balloon, having some holes in it, at its lower
end. On pushing down the piston, you will observe that the water comes out of the same forces in all the direction from the
various holes. What do you conclude? Explain with a neat sketch. We conclude that the pressure applied at any point on a liquid, present in a closed vessel is transmitted equally in all the
directions. (draw the figure 12.9 pressure of a liquid in a closed vessel is transmitted equally in all directions)
390
Explain an activity with the help of neat sketch to show an
pressure applied at one end of the water contained in the U-tube is transmitted equally in all directions.
A U-tube, with equal sized limbs, filled with water and fitted with two pistons as shown in the figure (Draw the Figure 12.20 of the text book: Pressure applied at one end of the tube is transmitted
equally in all directions.) When one kg weight is keep on one piston it is observed that this piston starts moving downwards and other piston starts
moving upwards. This upward movement of the other piston stops only another one kg weight keep on it as well. This shows
that the pressure applied at one end of the water contained in the U-tube is transmitted equally in all directions. Thus the pressure applied at any point on an enclosed liquid is
transmitted equally throughout the liquid. 391
State Pascal's law According to Pascal’s Law, the pressure exerted at any point on
an enclosed liquid is transmitted equally in all directions throughout the liquid. What are the uses of Pascal Law Many practical devices such as hydraulic Jack / lift , the hydraulic brakes and the Brahma press used to press bales of
cotton , etc make use of Pascal’s Law.
392
What is monometer? Describe its construction and working with the help of a neat sketch.
Manometer is a simple device used for measuring pressure. It is made by taking a U-tube with equal-sized limbs. The U-tube is
fixed on a suitable wooden stand. A suitable scale is placed in between the two limbs of the U-Tube. The U-tube is (about half) filled with coloured liquid. We find the level of the liquid is the same in the
two limbs when both the ends of U-tube are ‘open to the atmosphere’. As shown in the figure (next page)
However, if a rubber tube connected to a pump is fitted on one of the limbs on the U-tube and the pump is compressed, the level of the liquid in this limb goes down and in the other limb, it goes up. When one of the limbs is connected to a vessel that is being evacuated , the level of the liquid in it goes up. The difference in the levels of the
liquid in the two limbs of the U-Tube can be used to measure the pressure of a gas connected in a vessel.
393
394
How can you make a simple improvised pressure detector by using a U-tube show it?
An U-tube will be taken and (half) fill it with water. Add some crystal of potassium permanganate for colouring the water. Now fix this U-tube on a Thermocol board. Fix a (correct size)
strip of centimetre graph paper between the two limbs of the Utube. Thus our simple pressure detector is ready. Connect one side of this U-tube to the opening of a partially
filled up football (use your imagination and improvisation for making this connection). You will find the water level in this
limb goes down. Note the difference in the label of coloured water of the U-tube on the graph paper scale. This differences indicate that the differences in the pressure of the air inside
the football and the outside atmospheric air. (draw Figure 12.23 of the text book: A pressure detector) 395
Back to contents 396
1. What type of sound we hear every day?
We hear different types of sounds- the sounds of the morning alarm , the chirping of birds, the voice of parents asking children to get out of their beds, the teacher teaching in the
class, the horns of the cars and the buses on the road, the barking of dogs, the mooing of cows and the songs on the radio
or tape recorder and many more. 2. What is the difference between Music and Noise? Sound which produces soothing or pleasant effect are called
musical sound or simply music and the sound which produces an unpleasant effect is known as noise.
3. What is sound? Sound is something that produces a sensation of hearing in your ears. 397
4. Vibration is the source of sound, explain?
It turns out that whenever an object is producing sound, it has a ‘to and fro’ motion associated with it. We can thus say that the sounds are produced by making an object move to and fro that is by making them vibrate. We can therefore, regard vibration as the source or the cause of sound. 5. Explain an activity to show with a sketch that vibrating object produces sound.
A ruler is taken and its one end is pressed on the table with your left
hand and the other free end of the ruler is Pulled with the right hand and let it go. It is observed that the ruler is seen vibrating and a humming
sound
is heard. This is due to the humming
sound produced by the to and fro motion or the vibration of the ruler. 398
6. Give two example and explain an activity to show with a sketch that
vibrating object produces sound. (i) A rubber band is taken and it is held between the finger and the thumb as shown in the figure. Then the rubber band is Plucked . It is observed that The
plugged rubber band is seen moving to and fro and a humming sound is heard . The humming sound, here to
is clearly being produced by the vibrating rubber band. (ii) If a drum is struck one will hear the sound but do
not notice any to and fro motion of the drum skin or membrane. Now if some small thermocol balls are put on the drum and struck it again it is observed that a sound is heard and the thermocol balls are jumping up and down on the drum skin or membrane. The jumping
balls show that the skin of the drum is vibrating. Thus , when a drum is producing sound, its skin is in a state
of vibration. 399
7. What is tuning fork A tuning fork is made up of two metal prongs,
bent into a U shape, with a stem at its lower end. It is a simple instrument used to produce
a pure sound. 8. Explain an activity making use of a tuning fork to show that the prongs of a tuning fork are vibrating when it is producing sound. If a tuning fork is struck lightly against a rubber pad one can hear its pure musical sound but are not easily able to see any vibration. If the prongs
of a sounding tuning fork are touched to a bead which is suspended from a string as shown in the
figure the bead files away, which indicates that the prongs of a tuning fork are vibrating when it is producing sound. 400
9. Give two examples to show that the prongs of a tuning fork are
vibrating when it is producing sound. (i) When the prongs of the sounding tuning fork is put just below the surface of water in a beaker it is
observed that water is bubbling and vibrating this indicates that the sound is produced sue to the
vibrations in the prongs of a sounding tuning fork. (ii) Some wax is attached to the pin fixed on the prongs of a tuning fork. When the tuning fork is struck lightly against a rubber pad it will produce sound. Now if the pin of the prong of the tuning fork is lightly touched against a piece of blackened glass, a wavy line is traced on the glass.
This indicates that when a tuning fork is producing sound it is vibrating. These experiments show that a body
producing sound is always in a state of vibration. Whenever the vibration of the
body stop, the sound produced by it also stops.
401
10. What is Oscillation? Give an example. Repeated ‘to and fro’ motion of a body is called oscillation. The
swing on which children play is in a state of oscillation. A simple pendulum is another example of oscillating body. 11. What is simple pendulum? A simple pendulum consists of a weight,
called bob, suspended by a thread. We can make a simple pendulum by taking a metal bob (provided with a hook) and
tying a string to it. This combination, when
suspended
from
a
stand
or
a
support, becomes a simple pendulum. If we displace this metal bob to one side and then let it go, it starts oscillating and
keeps on oscillating for sometime. 402
12. What is Amplitude? The Amplitude of a sound equals to the maximum
displacement of the vibrating source from its normal or mean position. The a magnitude of
displacement
from
mean
position
‘O’
to
is
maximum when the bob is either at ‘A’ or at ‘B’. This maximum displacement of vibrating particle
from its mean position is known as Amplitude. 13. How amplitude is related to the sound? The amplitude determines the loudness of the sound produced
by the body. The more the amplitude of a vibrating body, the louder is the sound produced by it.
403
14. Explain one oscillation.
In the oscillation of a swing or the pendulum of a wall clock , they go to one extreme ‘A’, come back to ‘O’, go to the other extreme ‘B’, on the other side, again come back to ‘O’ and again go to the first extreme ‘A’. The One complete cycle of motion (A-O-B-O-A) of the oscillating body is known as one oscillation.
15. What is Time period? What is its unit of measurement? The time period of an oscillating body is the time taken by it to complete one cycle of its to and fro motion that is to complete one oscillation. It is measured in units of second. 16. What is frequency? What is its unit of measurement?
The frequency of a sound equals the number of vibrations completed by its source in once second or the frequency of an oscillating body is the
number complete oscillation made by it in second. it is measured in units of Hertz (Hz). 404
17. Frequency of an oscillating body is 50 Hz, explain. It implies that it can complete 50 oscillation in one second, that
is, takes just 1/50 second to complete one oscillation. 18. What is the relation of frequency of the vibrating sound with
sound? The frequency of a given sound determine sharpness or shrillness of sound. If we increase the frequency of vibration,
the sound produced becomes sharpener and shriller. Decrease in frequency, on the other hand tends to make the sound flat.
19. What is Pitch? How it is related with frequency of sound? The pitch of a sound is that characteristic of the sound which determines the extent of it shrillness or flatness. Higher pitch
produces shriller sound and lower pitch produces flatter sound. If frequency of the sound is high the pith is high and if the frequency of the sound is less pitch is low. 405
20. What is the frequency of human voice in general? Is the frequency of voice of a male and female and babies are similar? The frequency of the human voice generally lies between 1000 Hz and 1500 Hz. The frequency of a female voice is generally more than that of the all male voice. Thus female voice is a higher pitch and small babies have an even higher pitch.
21. The light of the sun and the stars is able to reach us but we can not hear sounds of any event that may be taking place in these heavenly
bodies, why? While The atmosphere of the earth extends only to a height of a few
hundred kilometres. There is no air or any other medium beyond that, that is, there is a vacuum in outer space. The light of the sun and the stars is able to reach even though this vacuum because light can travel through vacuum, sound cannot do so. Sound needs a medium for propagation. therefore we do not keep on getting sounds of any event
that may be taking place in these heavenly bodies. 406
22. How astronauts talk to one another in moon?
The moon has no air or atmosphere. it is, all vacuum on its surface. So astronauts cannot talk directly to one another on the moon, they communicate through wireless sets using radio waves, which
can travel through vacuum. 23. What are the mediums which sound can propagate?
Sound an travels through gases like air, through liquids and solids. 24. Explain an activity to check that sound travels through liquid also? Two wooden blocks or two stones are taken and when these are struck together one can hear the sound produced by them. These
are then held in a tub of water and strike them again and when one press his ear to the side of the tub a clear sound. Can be heard.
This clearly indicated that the sound reached the ear through water. 407
25. Explain an activity to show that Sound needs a medium for
propagation to show that Sound needs a medium for propagation. An arrangement is made as shown in the figure. When the bells is connected to the battery or a source of electricity, it starts ringing. If
the vacuum pump inside the jar is started it starts evacuating air from the jar in which the bell is kept. It is observed that the sound of
the bell keeps on getting the dimmer and dimmer. After some time the sound of the bell is not audible at all but still the hammer can be seen vibrating. If the vacuum pump is stopped now and the jar is removed the sound of the bell is again audible. This is so, because a sound, associated with
the vibrating bell, does not reach us when the air around it is removed. Its sound can reach
us only when there is air around it. Thus, sound needs a medium for its propagation. 408
26. Give an example that shows sound can travel through liquids. Marine animals like dolphins and whales communicate with one
another, even when they are far away from each other. This is due to the fact that sound can travel through liquids. 27. Give an example that shows sound can travel through solids faster than air. People living near railway tracks often press their ears against
the track. This helps them to detect whether a train is coming or not. This way they can often predict the arrival of the train long before it is seen or heard. This is because the sound produced by
the moving wheels of trains travels much faster through the track. Therefore, it is heard through the track much before it is
heard through the air. This shows that sound travels faster through solids. 409
28. Explain an activity that demonstrate the passage of sound through solids.
A toy telephone is made by taking two empty and clean ice cream cups. A small hole at the bottom of each cup is made and a long string is passed through them. A knot or a match box is tied at each end so that the string does not slip through the holes. These cups are used as two telephones and two person can talk to themselves
standing at a distance while keeping the thread stretched tightly. One may not be able to hear voice of other directly through air but
able to hear him quite clearly through this telephone. The voice now reaches through the string connecting the two cups. 29. Speed of sound depends on which factor?
The speed of sound depends upon the nature of the medium through which it travels. In general, sound travels slowly in gases, faster in
liquids and fastest in solids. 410
30. What is the sound of iron , water and air Medium
Speed of sound
Iron
5000 metre per second
Water
1500 metre per second
Air
340 metre per second
31. What are the types of sound? There are two types of sound (i) Audible and (ii) Inaudible sounds
•
Audible sounds- All sound that we can hear through our ears are known as audible sounds.
•
Inaudible sounds - All sound that we fail to hear through our ears are known as inaudible sounds.
411
32. What is threshold of hearing? An audible sound has to have a certain minimum loudness. We call this minimum loudness, that the human ear is able to detect, the threshold of hearing. It has the same value for normal human ears. A sound less louder than the threshold of hearing is , therefore , an inaudible sound. 33. Explain an activity to show that is not only the amplitude of a
vibrating body but also its frequency that decides whether it is going to produce an audible or an inaudible sound.
A simple pendulum has been made by attaching a metal bob to a one metre long string. This pendulum can make to oscillate by taking its bob
to one side and then letting it go. The oscillating simple pendulum is a vibrating body. It could, therefore, be a source of sound. However, even if we increase the amplitude of this Pendulum up to its maximum limit, the sound could not be heard. This is due the fact that not only the amplitude of a vibrating body but also its frequency that decides whether it is going
to produce an audible or an inaudible sound. 412
34. Define audible and in-audible sound in terms of threshold of hearing and its frequency.
•
Audible sound - if its loudness is equal to or more than the threshold of hearing and its frequency lies between 20 Hz
and 20,000 Hz. •
Inaudible sound - if its loudness is less than the threshold of hearing and its frequency is less than 20 Hz or more than
(nearly) 20,000 Hz. 35. What are infrasonic and ultrasonic sound?
•
Infrasonic sound- Inaudible sound having a frequency less than 20 Hz are known as infrasonic sound.
•
Ultrasonic sound - Inaudible sound having a frequency more
than 20,000 Hz are known as ultrasonic.
413
36. Write some uses of Ultrasonic sound.
Ultrasonic sound are of great use to animals like bats. Bats are able to find their way at night by producing and detecting sounds of frequency more than 20000 Hz. Animals like leopards, monkey, deer and dogs can also hear ultrasonic. 37. What is Galton’s whistle?
There are special whistle, known as Galton’s whistle, that can produce sounds of frequency more than 20,000 Hz. The owners of the dogs can
use these whistle to give signals to the dogs without knowledge of any person standing nearby. 38. What are the difference between noise and music Noise is an unpleasant sound and that often produces an irritating sound effect us.
Sounds, which produces a pleasing and relaxing effect are called musical Sound or simply music. Thu musical sound or music is a
pleasant sound that produces a soothing and relaxing effect on us. 414
39. What are the causes of difference between the musical sound and noise? The reason for the difference between the musical sound and noise is that, a musical sound originates from a source that vibrates in a very systematic way. There is sense of continuity and rhythm in its vibration and there are no sudden breaks or jerks. On the other hand, noise arises from the vibrations that are quite irregular and often have a sense of
discontinuity with sudden breaks or jerks coming in a random and unpredictable manner.
40. Why we should make efforts to reduce noise? Is loud music desirable?
Music makes one feel very happy. There are a number of reasons to believe that musical sound improve our health and keep in a positive frame of mind. In fact music is now regarded as health tonic. Therefore, we should make efforts to reduce noise and to have more of soothing soft musical sound around us. However, remember that loud music too is not
desirable. 415
41. Which factors affects the nature of a sound? The overall effect of sound on as is determined mainly by three factors
(i) the loudness (ii) the pitch and
(iii) the quality of that sound. 42. On which factor loudness of a sound depends? The loudness of a sound depends on the amplitude of vibration of its source. The more the amplitude, the louder is the sound. 43. On which factor frequency of a sound depends?
The pitch of a sound decided its shrillness or flatness. It depends on the frequency of the sound source.
44. On which factor quality of a sound depends? The quality of the sound is determined by the combination of all the frequencies and their relative loudness. It determines the overall
character of the sound. 416
45. What is the unit of measurement of sound? Loudness of sound is measured in decibels(dB).
46. What are the loudness of following sound? Breathing, Radio Music, Loud noise, Traffic noise, Aircraft Noise. Sound
Loudness in dB
Breathing
10
Radio music
50
Loud noise
60
Traffic noise
60- 90
Aircraft noise
120
47. Why we rarely forget a sound having heard it once? Each sound is a characteristic of the object that produces it.
Because of this we rarely forget a sound having heard it once. We can quickly recognised that sound when we hear it again we can
recognise a person from the sound of his voice even without seeing him.
417
48. Explain one activity to show that sound depends upon loudness and pitch. (i) One drum is taken and some ping-pong balls are placed on it. When the drum lightly struck and then more forcefully, it is observed that the ping pong ball dance a little. A low sound is produced when the drum was struck lightly. When the drum was struck forcefully the ping pong balls dance violently and sound produced is louder. Thus loudness of a sound
increases with an increase in the amplitude of vibration of a vibrating body. Now, if two drums are taken , one small and one big and vibrate
them with same amplitude. It is observed that you get louder sound from the bigger drum. Thus loudness of a sound also increases with an increase
in the area of the vibrating body. (ii) One bicycle is taken and is place upside down. At first the wheel is slowly rotated and then rotated faster and the spokes are touched lightly with a ruler it is observed that a low sound is produced when the wheel is rotating slowly. A shrill sound with higher pitch is heard when the wheel is
rotating faster. Thus the pitch of a sound increases with frequency. 418
49. Give an example to show that pitch of a sound increases with an increase in the frequency of vibration.
A postcard is rubbed against a comb teeth slowly. A low sound is produced. When the same postcard is rubbed faster against the comb teeth rapidly it is observed that a the pitch of the sound is
increased. Thus the pitch of a sound increases with an increase in the frequency of vibration.
50. Name some of the various type of musical instrument. Are the overall quality or character of the sound produced by each same? Various musical instruments are - for example the sitar, the drum,
the flute and harmonium. They all produces pleasant musical sound but overall quality or character of the sound produced by each has unique nature of its own.
51. Who is Amjad Ali Khan? He is a maestro of sarod. 419
52. What is string instruments? How sitar produces sound?
The Sitar is an example of a category of musical instruments known as string instruments. We pluck the string in a sitar to produce its sound. By adjusting the length and tension of the
string, we can change the overall quality of the sound produced by it. However, its sound is always pleasing and soothing. 53. How the sound is produced by a guitar, the piano and the
violin? The guitar, the piano and the violin are some other string
instruments. As in a sitar, we pluck the string in guitar to make it vibrate. However we strike the strings (key) in a piano and draw a bar across the strings in a violin to make them vibrate.
420
54. What is percussion musical instrument? How sound is produced by it? Give some example
A drum is an example of percussion musical instrument. In such instruments we make a leather membrane to vibrate by striking it either with a hammer or a stick or with hands. The sound produced by a drum is a musical rhythmic sound. The tabla, the dholak and the dafli are some of other percussion instruments.
55. What are wind instruments? Give some example. The flute is a well-known example of this category. It is in the form of a hollow pipe. There are a suitable number of carefully
and correctly positioned holes in this pipe. We blow the air through this pipe and closing the holes properly, we get different
pleasing and, melodious notes through it. The whistle, the clarinet and the Shehnai are some other example of wind instrument. 421
56. Who is Zakir Hussain? He is an well-known maestro of Tabla.
57. Who is Hariprasad Chaurasia? He is well known maestro of flute. 58. Who was Ustad Bismillah Khan?
He was a well known maestro of Shehnai . 59. What are reed instrument? Give some example. We also have musical instruments like the harmonium and the
mouth organ. They belong to a category known as the reed instrument. They contain metal reeds which produce pleasing
sounds when air is blown through them.
422
60. What are the ways by which musical instruments produces sound?
Musical instruments produce sound in four ways. •
by vibrating strings,
•
by vibrating membranes
•
by vibrating columns of air, and
•
by vibrating metal reads.
61. How music can be produced from the bowl made of china clay? What is the name of this type of musical instrument. Seven small bawls made from china clay are taken and water is
poured up to different levels in each bowl. These bowls now arranged in a series starting from the least filled to the maximum
filled. When with the help of two wooden sticks, the bowls are struck gently over one by one, a musical sound can be heard. This type of instrument is known as Jal Tarang. 423
62. How sound is produced by human beings? Sound is associated with what vibrations. We have two vocal
cords stretched across the voice box in our throat. When our lungs force air through them, they vibrate and produce sound. The vocal cords behave like strings of a musical instrument.
When these are completely relaxed, air passes out between them without vibrating them and without producing any sound. When they are stretched , they vibrate and produce sound. The
variation in the in the pitch are due to the variation in the degree of stretching of the vocal cords achieved automatically, when we
talk or when we sing. 63. Why female voice is high pitched and that of male? The vocal cords of women are shorter than those of the man.
This is the reason why female voice is high pitched and that of male is low-pitched. 424
64. How sound is produced by animals?
Some animals also makes sounds with the help of their voice boxes. Birds chirp or sing and frog croak with the help of voice boxes.
While croaking frogs puff up their throat like a balloon, and a bird’s lungs force air through its voice boxes. All animals do not necessarily have a voice box, for example
bees have no voice boxes. They make sound by moving their wings up and down very fast and so do the mosquitoes.
However, the grasshoppers rub their legs against their wings to produce sound. 65. Name the produced by some animals.
Sound produced by different animals areDogs bark, Cats mew, Lions roar, Cows moo, Birds chirps, Mosquito buzz, The cuckoo sings and so on. 425
66. Give an example that it is possible to guess the well being and mental state of different animals by the changes in the quality of their sounds at
different times. It is possible to guess the well being and mental state of different animals by the changes in the quality of their sounds at different times. This is also true for human beings. For example, a mother knows the difference between the cry of a child when the child is hungry, in pain or discomfort. Specialist can tell us a lot about the animals and the birds from the sounds they are producing at any given time. From the sound produced by
a buzzing of bee wings, experienced beekeepers can know whether the bees are going for money or are returning to the beehive. When the bees
are going to for honey , they are lighter and they buzz their wing faster. Therefore, the sound produced by them is of higher pitch. When they
returning to the beehive they are loaded with honey and, therefore, are heavier, so they buzz their wings at a slower rate and produce sound of a lower pitch. An experienced beekeeper can detect this change in pitch and, therefore, come to the correct conclusion 426
67. Why noise pollution a health hazard?
Doctors and all other health experts , tell us that noise is a health hazard . It makes us irritable and adds to our level of mental
tension.
It is harmful for our ears and other body organs. Noise
pollution can lead to lack of sleep, high blood pressure, anxiety or even temporary or permanent impairment of hearing.
68. How we can reduce noise pollution? We should try to identify the main sources of noise in our
neighborhood and try to minimise their noise level. This would help us to save ourselves from this new health hazard. 69. Give some examples of noise and music Noise- Honking of vehicle’s horn in a traffic jam, street dogs start barking to one another , there is a neighborhood fighting where men
and women are shouting loudly and simultaneously at one another. Music - listening to a sarod recital by Amjad Ali Khan or a live
concert by Lata Mangeshkar 427
70. Is the plugging for ears with cotton wool will save us from the harmful effects of loud and noisy sound? What is the best
way to protect our ears from the harmful effect? The common notation that plugging for ears with cotton wool will save us from the harmful effects of loud and noisy sound is
not quit correct. This, at the best, has only a partial shielding effect. The best way to protect our ears from the harmful effects of loud and noisy sounds is to avoid them all together.
71. What are the bass and treble controls of a radio or a music system?
The bass control make the sound flatter, the treble control makes the sound sharper. By adjusting these two control desired quality of sound is obtained.
428
Key word. 1. Amplitude- Mean displacement from the ‘mean’ or ‘normal’ position of a vibrating body
2. Audible sound- Sound that we can hear through our ears. 3. Frequency- Number of complete oscillation made by a body in one second.
4. Inaudible sound - sound that we cannot hear through our ears. 5. Infrasonic- Inaudible sounds,
having a frequency
less than 20 Hz. 6. Music- A pleasant sound that often produces a
soothing relaxing effect.
429
7. Noise- An unpleasant sound that often produces and irritating affect human beings.
8. oscillation- ‘To and fro’ movement repeatedly from one position to another and back again 9. Sound - something that produces the sensation of hearing in our ears.
10. Time periods- The time taken by a body to complete on cycle for its ‘to and fro’ motion. 11. Tuning fork : an instrument used to produce a pure
sound. 12. Ultrasonics- Inaudible sound having a frequency greater than 20000 Hz.
430
Round Up.
1. We live in a world full of sounds. Some of the sounds are pleasant , while the others are unpleasant. 2. We often say that often say that sound is a something
that
produces
the
sensation
of
hearing in our in our ears. We make sounds by
things to move ‘to and fro’ that is by making them vibrate. 3. Sound is consequence of the vibration of any object in a medium . 431
4. The amplitude of an oscillation by is equal to its maximum displacement from its mean or normal position. 5. The loudness of a sound is determined by the amplitude of the vibrating body produces it.
6. The frequency of vibration of a vibrating body control the pitch of the sound produced by it. 7. Sound cannot travel through vacuum. 8 Sound can travel through solids, liquids and gases 432
9. Sounds are audible or inaudible, depending upon
their amplitude and frequency 10. A normal ear can hear sounds of frequencies from 20 Hz to 20,000 Hz. These frequencies make up the sonic sounds.
11. Sound frequencies are greater than 20,000 Hz are called ultrasonics, while those of frequencies less than 20 Hz are for infrasonics. 12. Some animals like dogs, leopards, bats, deer and
monkeys can hear ultrasonic sounds. Bats , in particular make use of ultrasonic sound for finding their way around. 433
13. we call a pleasant sound music on musical sound, We use musical instruments to produce
such sounds. 14. Very loud sounds are harmful for our ears. 15. Loudness, which depends on amplitude, is a physiological effect of a sound 16.
Quality
of
sound
is
determined
by
the
amplitude and frequency of different components
present in it.
434
Evaluate your grasp 1. what is the cause of sound? 2. Define the term ‘amplitude’.
3. Define the term ‘time period, 4.
What
is
the
unit
of
time
period
and
frequency? 5. Which property of sound is related to its amplitude?
6. Which property of sound is related to its frequency?
435
Evaluate your grasp 1. Can sound through vacuum? 2. State the condition under which can give
sound is •audible and •inaudible 3. What is the mean by noise? 4. What kind of source produces a musical sound?
5. Name the three factors which affect the nature of a given sound. 436
Judge yourself judge yourself A) Answer the following question 1. Name
some
pleasant
and
some
unpleasant
sounds 2. What effect does an increasing frequency have
on the sound produced? 3. Define the following terms: (a) audible sound and (b) inaudible sound 4. Name two properties which decide whether a
given sound is audible or inaudible 5. Name the states of matter in which sound travels the (a)fasted and (b) slowest. 437
B) Answer the following questions in detail. 1. Describe an experiment to show that a body producing sound is in a state of vibration.
2. What is the tuning fork? What is its special property? 3. What is the role of bass and treble controls of music system?
4. Describe an experiment to show that sound needs a material medium for its propagation 5. Is noise pollution a health hazard? What can you do to minimise noise?
438
C. State whether the following statements are true or false. If false give the correct statement. 1. Of the three states of matter, sound travels the
faster through gases. 2. The lower the frequency of vibration of the body, the more shrill is the sound produced by it 3. The sound is in a sitar is produced by plucking its
string. 4. It is only the extent of “loudness’ of a given sound that determines whether it is audible or inaudible. 5. Noise pollution is now regarded as a serious
health hazards. 439
Back to contents 440
1. What is sky? The vast void or empty space above the earth is known as the
sky. The sky has a special blue colour of its own. During the day, we often see clouds floating in the sky. The bright Sun that lights up the day and provides us lots of light and heat. The
appearance of the sky changes dramatically after the sunset. Moon whose size keeps on varying night after night and a large
number of tiny shining stars scattered throughout the sky. 2. What are stars? Why stars are look tiny? Why they are not visible on day? Stars are bright objects like the sun?
Many of these stars are much bigger and brighter than the sun. But these stars are much farther from the earth than is the sun. That is the reason these stars look tiny and dim in
comparison to the sun . This is also why they are not visible in the bright sunlight. 441
3. What are planets? What are the major difference between stars and planets ?
The stars are often seen as twinkling. We can also observe some tiny shining objects that do not twinkle. These are the planets. The major difference between
stars and planets is that stars
have their own light while planets do not. Planets shine because of the sunlight reflected from their surface.
4. What are called celestial objects or heavenly bodies? The moon, the planets, the stars and other smaller bodies make up the sky and are called celestial objects or heavenly bodies.
5. What is universe? How big is it? Everything that you can see is in the universe. The whole of
space is called the universe. It is so big that it is difficult to imagine. Actually we do not know exactly how big the universe is. 442
6. What Solar system consists of? The solar system consists of the sun, the eight planets and
their satellites (or moons) and thousands of other smaller heavenly bodies such as asteroids, comets and meteors.
7. What is orbit? Which planet have smallest and which planet have largest orbit? The planets revolve around the sun in somewhat elongated
oval-shaped
or
elliptical
paths
called
orbits.
The
orbits,
however, have different sizes - the orbit of Mercury is the smallest and that of Neptune is the largest.
8. Name the planets in ascending order of their distance from the sun?
In ascending order of their distance from the sun, the 8 planets are
Mercury
,Venus,
Mars
,Jupiter
,Saturn,
Uranus,
and
Neptune . 443
9. What is Milky Way Galaxy? How many galaxies are their in the solar
family? The
solar
family
is
just
one
member
of
a
group
of
about
1,00,00,00,00,000 (100 billion) stars known as the Milky Way Galaxy. This Galaxy (a group of very large number of stars) is not the only Galaxy in the universe. It has now been estimated that there are at least a thousand million of such galaxies, each containing from a few hundred million to a few thousand million stars .
10. What is the unit for measuring distances between celestial objects? Explain.
The celestial objects are separated from one another by very large distances. For example, the distance of the sun from the earth is
approximately 15,00,00,000 km. The distances of stars and other celestial objects outside the solar system are even larger. Kilometre is, therefore, not an appropriate unit for measuring such large distances. The unit often used for measuring distances between celestial of date is a light year. 444
11. Define one light year? One light year is defined as the distance, moved by light, in one year.
12. What is the speed of light? The speed of light is 300,000 Km per second.(3 x 10-8 m/s). This is the limit for the highest speed that can be achieved in the entire universe. No other object can ever surpass the speed of light. 13.How much time it takes by the light from the sun to reach the
earth? The light from the sun takes about eight minutes to reach the earth.
14. What is the distance of the sun from the earth on Light years? The distance of the sun , from the earth , is eight Light minutes. 15. A star is twenty light years away from the earth. Explain it.
A star is twenty light years away from the earth means , that the distance is such that the light, from that star takes twenty years to
reach the earth. 445
16. Why The Sun looks much larger than stars?
Sun looks much larger because it is millions of times closer to the earth than the other stars. It is only a medium sized star. Some stars are much bigger.
17. The sun is in the centre of the solar system, explain. The sun is in the centre of the solar system. It has a gravity
which pulls on the planets and keeps the solar system together. Million of objects travel around it. The biggest of these are the eight primary planets. Each planet rotates as it revolves around
the sun. 18. Which member is the largest and the heaviest member on the
solar system. The sun is the largest and the heaviest member of our solar system. 446
19. What is nuclear fusion? The outer surface of the sun is at a temperature of nearly 6,000
K. Its inner core is much hotter. The hydrogen nuclei, present in the sun, fuse together to form helium nuclei. This reaction is called nuclear fusion. 20. Without the sun's warmth and energy , no living things could survive on the earth, explain.
The
hydrogen nuclei, present in the sun, fuse together to form
helium nuclei. This reaction is called nuclear fusion. It is this reaction that generates the heat and light energy radiated by the
sun. Without the sun's warmth and energy , no living things could survive on the earth. The sun powers the water cycle and keeps
the air moving on the earth.
447
21. Why earth also shines like other stars when seen from the
surface of the moon? The sun is the source of heat and light for all the planets and their satellites. Some of this light is reflected back to make them
shine and become visible. That’s is the reason why earth also shines like other stars when seen from the surface of the moon? 22. Compare physical quantities of earth and sun?
The sun is very large and massive compared to the earth. The average density of the sun is about 1/4 the average density of
the earth, but its mass is more than a million times the mass of the earth, and its diameter is about a hundred times that of the earth.
23. What is planet? A planet is a heavenly or celestial body moving around the sun
and reflects light from the sun. 448
24. How many planets are their in solar system? There are 8 planets in our solar system. 25. What is the shape of a planet? why ? All of these are round. They are made round by gravity.
26. What are the groups of planets based on their distances from the sun? Explain the each group.
Based on their distances from the sun, planets have been divided into two groups. inner planets and outer planets. The planets Mercury, Venus, Earth and Mars, all receive substantial
amount of solar energy and are known as the inner planets. All of these four are made up of rocks hard enough to stand on.
The other 4 planets Jupiter, Saturn, Uranus and Neptune are comparatively too far away from the sun and are known as the outer planets. These four planets are made of gas or liquid. One cannot stand on them 449
27. Why Pluto is called as dwarf planet?
Pluto was once thought to be a planet. Now it is called a dwarf planet. It also orbits around the sun at a much farther distance than the eight primary planets. 28. Which planet is the nearest to the sun? Mercury is nearest to the sun. 29. Which planet has the highest revolving speed? Mercury has the highest revolving speed among all the planets.
30. When we can see mercury planet in the sky? It is visible in the sky, very close to the horizon for a short period, just
before sunrise or just after sunset. 31. Why one part of the mercury planet has always day and is very hot?
The Mercury always projects the same side to the sun so that its one part always has day and is very hot. 32. What is the colour of mercury? It is yellowish Orange in colour. 450
33. Which planet is the smallest in the solar system? Mercury is the smallest planet in the solar system.
34. What is the geographical feature of Mercury? Mercury has craters everywhere.
35. What is temperature of mercury in the sun facing side? It is hot , 427C on the sun facing side. 36. Describe Mercury or Budh.
Mercury is nearest to the sun and its revolving speed is the highest of all the
planets. It is visible in the sky , very close to the horizon for a short period , just before sunrise or just after sunset. It
always projects the same side to the sun so that its one part always has day and is very hot. It is yellowish Orange in colour. 451
37. Which planet is the brightest of all the planets? Venus is the brightest of all the planets. 38. What is the colour of the Venus? It is a silvery blue in colour 39. What is the surface temperature of Venus? Venus is a very hot planet. Its surface temperature is around 480
degrees Celsius. 40. Why Venus is often called a Morning or an Evening Star?
Venus can be seen up to 4 hours before sunrise or 4 hours after sunset, but never late at night. So, it is often called a Morning or an Evening
Star. 41. Why Venus is brightest of all the celestial bodies? Venus is even Brighter than the mercury and is, therefore, the brightest of all the celestial bodies visible in the night sky except moon. Its brightness is associated with its cloudy atmosphere that is a very good
reflector of sunlight (almost 75% of the incident sunlight gets reflected by it) which falls on its surface. 452
42. What makes the Venus the hottest planet on the solar system?
Venus is covered with thick poisonous clouds. These clouds keep the heat in, so Venus is so hot 43. Describe the Venus or Shukra.
Venus is the brightest of all the planets. It is a silvery blue in colour and is a very hot planet. Its
surface
temperature
is
around
480 degrees celsius. Venus, like Mercury,
can be seen up to 4
hours before sunrise or 4 hours after sunset, but never late at
night. So, it is often called a Morning or an Evening Star. 453
44. What makes the Earth or Prithvi unique planet in the universe?
Earth is perhaps the only unique planet in the universe that contains oxygen and water - the two things necessary to sustain life . Astronauts have reported that the Earth looks like a
beautiful light blue ball from the moon. It is the only planet to have oceans. Earth is the only planet that has life on it. Plants
and
animals
need
water,
the
right
air,
and
the
perfect
temperature to survive. earth is the ideal place to live. 45. How earth is protected from the sun's rays?
Our planet is surrounded by a thick layer of gases , called the atmosphere, held in place by gravity. It is like a bubble protecting us from the sun's rays.
454
46. What are the two main motions associated with it? How much time is taken by each type of motion? The Earth has two main motions associated with it are revolution and rotation. •
Its revolution around the sun for which it takes nearly 365.25
days(1 year) and •
Its rotation about its own axis which takes nearly 24 hours (1 day). It is the combined effect of these two motions that bring about changes in seasons.
47. In what way the earth’s rotation is associated with the seasons
of the earth? The axis of rotation of earth remains tilted in the same direction
throughout its revolution around the sun. When the northern hemisphere is tilted towards the sun, it is summer season there and winter in the southern hemisphere. The reverse happens when the
southern hemisphere is tilted towards the sun. 455
48. What is earth’s equatorial plane and orbital plane? How
they are related explain with a sketch. The plane in which earth’s equator lies is called the equatorial plane.
The plane containing the orbit of the earth around the Sun is called the orbital plane. The
two
planes
do
not
coincide nor are they are parallel, they are inclined to each other at an angle
of 23.5 degree. This means that the axis of earth is
tilted at an angle of 23.5 degrees
with
respect
to
the vertical line. 456
49. What is the colour of the Mars? Mars is a reddish-orange planet. 50. What we know Mars ? Although it looks red hot, it is actually very very cold. It has valleys and volcanoes like the earth. Mars has canyons, which may have once been
rivers. There is some evidence of presence of snow on Mars. Huge red dust storms rage over its surface. There are certain blue , green and grey
regions over the Mars’ surface. 51.Why we know a lot more about this planet than about others?
We know a lot more about Mars than about others because of its favourable positions, it comes as close as within 5,60,00,000 km of the earth. 52. What are the evidence considered that there is some sort of life in mars? There is some evidence of presence of snow on Mars. If there was water, there may also have been life. There are certain blue, green and grey
regions over the Mars’ surface. These are often considered as an evidence of some sort of life on Mars.
457
53. Which one is the biggest planet of the solar system? How
much nigger is it? Jupiter is the biggest planet of the solar system, even bigger than all the other planets combined.
54. Why Jupiter is often referred to as icy giant of the sky? Jupiter is very cold and therefore is often referred to as icy
giant of the sky. 55. Describe the physical features of the planet Jupiter. Jupiter is the first of the four gas planets. Bright yellow and red
clouds swirl around it. Jupiter has no hard surface at all. It has 67 moons, of which, the largest four can often be seen with a
pair of binoculars. It also has faint rings around it. 56. What happens if astronauts flew to Jupiter? If astronauts flew to Jupiter, they would find no where to land. 458
57. What is great red spot? Jupiter has a great red spot, which is a giant swirling storm.
58. When Jupiter can be seen on the sky? Jupiter can be seen as a very bright star for about half the year in the evening sky.
59. What is size and temperature of Jupiter? Saturn is the next in size to Jupiter and is also a very cold planet.
60. What is the unique distinctive feature of Jupiter? Jupiter has a unique distinctive feature from the rest of the planets, i.e., a system of rings around it. Because of these rings
Saturn is one of the most fascinating and impressive objects in the night sky. 61. What is the colour and density of Jupiter?
It appears yellowish in colour and has a density even less than that of water. 459
62. How many moon Saturn has? Which is the biggest moon of Jupiter?
Saturn has many moons. These number is believed to be 62, though there may be more. All of these are quite small except for
one call Titan, which is a little larger than the earth's moon. 63.
When
Uranus
or
Indra
and
Neptune
or
Varuna
were
discovered?
These planets are only discovered during the 18th and 19th centuries after the invention of the telescope. 64. What are the similarities between Uranus and Neptune?
These planets are of twin size, with Uranus somewhat bigger than Neptune. They are called blue planets and are very cold.
Both are made up of gas and liquid. 65. Which planets are called blue planet ? Uranus and Neptune are called blue planets. 460
66. How is the weather of the Neptune? Neptune has the most violent weather in the solar system. Winds blowing at 2000 kph keep changing Neptune’s surface constantly. 67. Our ancestors were aware of 5 planets, which they are? What is
the Greek word of those planets? Our ancestors were aware of 5 planets that could be seen by the naked eye. These were Mercury , Venus , Mars , Jupiter and Saturn. The Greek word for these planets are wanderer. 68. Write a short note on Pluto.
Pluto was earlier considered as planet which was discovered in 1930. The most distant of the 9 planets (including Pluto). It is a
small object that receives almost no solar heat and is very cold indeed. Recently, it has been suggested that Pluto should not be regarded as a planet. There are reasons to believe that they Pluto
was once a moon of Neptune that escaped into its own orbit. It is not regarded as a planet now. 461
69 Fill up the table for inner planets MERCURY Diameter Distance from the sun
4,880 km
VENUS
EARTH
12,102 km 12,755 km
57 108 109 million km million km million km
MARS 6,795 km 228 million km
Revolution time
88 days
225 days
1 year
1.88 years (687 days )
Rotation time
59 days
243 days
24 hours
24.6 hours
None
None
One
Two
Number of moons
462
70. Fill up the table for Outer planets
Diameter Distance from the sun
JUPITER
SATURN
URANUS
NEPTUNE
142,984 km
120,540 km
51,118 km
49,495 km
778 1427 3000 million km million km million km
4,500 million km
Revolution time
12 years
29 years
84 years
165 years
Rotation time
10 hours
10.6 hours
17 hours
16 hours
Number of moons
79
62
27
14
Number of rings:
4
Thousand s
13
5
463
71. Which celestial body in the space is the nearest to earth ? The moon is the nearest to the earth in space.
72. What is a natural satellite? Give an example. A natural satellite is a heavenly body that revolves around a planet . Moon is a natural satellite of the earth. Of the eight planets, only Mercury and Venus have no satellite or moon. 73. What are the physical and geographical features of moon? The moon has no air or water on it. Its diameter is about four times lesser than the diameter of the earth and its mass is about eight times
lesser than the earth. It has no light of its own. It is observed that silvery glow is only due to the light of the sun reflected by its surface.
Its surface is covered with hard and loose dust and it has many uplands (mountains) and valleys that are filled with dry rock materials. Some of
them have heights comparable to those of the mountains on the earth. The moon is covered with craters where huge rocks called meteorites have hit it in the past. The moon has dark patches that we call seas, which are not filled with water like seas on the earth . 464
74. Why moon appears the biggest and brightest object in the night sky?
The moon is much smaller than stars but it appears the biggest and brightest object in the night sky because of its nearness. 75. How far is moon from earth?
Moon is about 3,84,400 kilometers away from earth. 76. Why the moon is covered with craters? The moon is covered with craters where huge rocks called
meteorites have hit it in the past. 77. What are the dark patches seen in the moon?
The moon has dark patches that we call seas, which are not filled with water like seas on the earth .
465
78. Why only one side of the moon is always seen from earth? The takes the same time,
27 days and 7 hours , to revolve
around the earth as well as to spin, or rotate once about its own axis. Therefore, we on the earth always see only one side, the front side, of the moon. It's other or back side is not visible
from the Earth.
466
79. Why we see various phases of the moon? The changes in the shape of the moon , or the various phases of
the moon are due to the (daily) change in its position relative to the sun. we see it in different shapes depending on how much
light shines on it. 80. How much time is taken for the transition from the new moon position to the full moon position?
The transition from the new moon position. when its other or back side is getting illuminated by the sun to the full moon
position , when its front side is getting illuminated by the sun, takes place is nearly 15 days. 81. How much time is taken by the moon to going back from new
moon position to the new moon again? The full cycle of going back to the new moon position from new moon position gets completed in 29 days and 12 hours. 467
468
82. What is ARMALCOLITE? ARMALCOLITE
is
an
Apollo
project
expeditions
to
moon.
The
various Apollo project expeditions have added to our wealth of Information and knowledge about the moon. One such expedition led to the discovery of a new mineral on the moon. This mineral was named as ARMALCOLITE in honour of the first three astronauts to walk on the surface of the moon. Neil Armstrong, Edwin Aldrin and Collins - on July 20, 1969.
83. Write a short notes on stars. A star is an extremely hot heavenly body that emits heat and light of his
own . It also appears to twinkling and has a regular motion of its own. Thus, a star is an extremely bright heavenly body that has a regular
motion and appears to twinkle in the sky. Beyond our solar system are billions of stars. Sun is the nearest star to our earth. The other stars appear very small to us due to their large distances from us. Most of the stars are very large objects having a spherical ball-like shape. Many of them are much bigger and massive
compared to the Sun. 469
84. What is pole star?
The Pole Star is a very special star in the northern hemisphere. It does not appear to show the (apparent) motion from the east to west like all the other stars do. It is known as the Dhruv Tara in
Hindi . The pole star ,present in the northern hemisphere, owes its name to a Greek word Polos which means Pivot. This star is
located at the north pole of the celestial spirit celestial sphere. 85. What are Constellations? There are many groups of stars which do not change their positions relative to one another. Therefore, such groups always have the same shape and relative orientation. It was thought that
these groups of stars resemble pictures of gods, animals or some other well-known objects. Each group was accordingly given a
name that indicated its similarity to some well known objects. These groups called constellations. Thus , a constellation is a group of stars forming recognizable shape or pattern. 470
86. What is the other name of Ursa Major? What is its Indian name? The other name of Ursa Major is Great Ursa and its Indian name is Vrihad Saptarishi. 87. What is the other name of Ursa minor? What is its Indian name?
The other name of major Ursa Minor is and its Indian name is Laghu Saptarishi or Dhruva Matsya. 88. What is Indian name of Scorpio? The Indian name of Scorpio is Vrischika. 89. What is the other name of Orion? What is its Indian name?
The other name of Orion is Hunter Vyada or Mriga. 90. What is the other name of Cassiopeia? What is its Indian name?
The other name of Cassiopeia is queen on her throne and its Indian name is Sarmishtha. 91. Which constellation is referred as summer constellation?
Ursa Major is referred to as a summer constellation. 471
92. When and in which part of sky Ursa Major can be seen in
sky? Ursa Major can be seen clearly in the northern part of the sky during the month of April.
93. What is the shape of the Major Ursa? Its shape seems to form the outline of a great bear and also
resembles a large ladle or a question mark. 94. How many stars are contained in Major Ursa? It contains 7 bright stars.
95. Which constellation is also called Big Dipper. Major Ursa is also called the Big Dipper.
96. How many stars are there in Ursa Minor? This constellation also contains 7 Stars but they are less Bright than those in the Ursa major 472
97. What is the shape of Ursa Minor? In this constellation, the 7 stars are close to each other and
appear to form the outline of a little bear. 98. When and in which part of the sky Ursa Minor can be seen? This constellation is seen in the summer season. It can be seen in the northern part of the sky during the month of July. 99. Why Ursa Minor is also called Pole star Constellation?
One of the seven stars in the Ursa Minor constellation is Pole
Star
itself.
We,
therefore,
also
call
this
Pole
the Star
Constellation .
100. How many stars are there in Scorpio? what is its shape look like?
This constellation is also a summer constellation and has 7 stars in it. these 7 stars are so arranged that they appear to resemble a scorpion . 473
101. When Orion is seen in the sky? This constellation is visible during the winter season. 102. How many stars are there in Orion? what is its shape look like? It has 7 prominent stars which appear to form the main body of a
hunter. There are some additional faint stars in this constellation which can be linked to the head and limbs of a hunter. 103. Which one is the brightest star in sky? Where is it located? Sirius is the brightest star in the sky. The star is located close to Orion.
104. How many stars are there in Cassiopeia? What is its shape? The 5 stars of this constellation appears to resemble the shape of a
queen sitting on her throne. 105. When Cassiopeia can be seen on the sky? We usually observe this constellation during the winter season.
474
106. What are Asteroid , Meteoroid and Comets There are some minor bodies in the solar system besides
planets and their moons. These are the asteroids , meteoroids and comets.
107. What is Asteroids? Where they are located? The asteroids or planetoids, are very minor planets that are found in great numbers in belt between orbits of Mars and
Jupiter. 108.What is Asteroids similarity with other planet? They revolve around the sun, too, just like all the planets do.
109. How one can observe Asteroids? These asteroids can only be seen through large telescopes.
475
110. What is Meteoroids? It is a very diverse group of small celestial bodies in the solar
system that moves around the sun. These are very
small
objects whose eccentric orbits can bring them into the earth’s
atmosphere. 111. Why meteors are known as shooting stars? The heat produced by their friction against the atmospheric air
causes them to get vaporized and produce a brilliant tail. For this reason, meteors are also known as shooting stars .
112. What are meteorites? Some meteors are large enough to survive and reach the earth’s surface. Such meteors are known as meteorites.
113.Why huge craters are formed in the earth? When a meteor hits the earth, it makes a huge crater.
476
114. What are known meteor showers? When earth crosses the tail of any comet, many a time a sea of
meteors is seen. These are known as meteor showers. 115. What is may be the one reason of died out of dinosaurs? It is assumed that the dinosaurs died out as a result of an enormous meteorite hitting the earth about 65 million years ago. 116. What are Comets?
A comet appears as a bright head with a long tail. Comets are very large but unsubstantial objects that develop very long tails when their orbits bring them close to the sun. The orbits of most
of the comet are such that they move around the sun once and the vanish, never to be seen again. But,some comets reappear at
regular intervals and are bright enough to be seen by the naked eye. 477
117. What is Halley’s Comet? When it was last appeared? When it will be appeared again?
The orbits of most of the comet are such that they move around the sun once and the vanish, never to be seen again. A few like Halley’s Comet are, however, exceptions to this. Halley’s comet made its last two appearances in 1910 and 1986. It is again expected to be visible around 2062.
118. What is satellites? Just as a celestial body which revolves around the sun is called a planet, in the same way, a celestial body that revolves around
a planet is called satellite. 119.When is the best time to spot the satellites in sky?
Just after dusk is a good time to spot the satellites. If the sky is clear , they look like moving stars. 478
120. What are the types of satellites ? How they differ? What are the similarities between them? Moon is a natural satellite of the earth. Similarly, many other planets have their own moon or moons. An artificial satellite is one which is
made by humans. There are many artificial satellites that are revolving around the earth. All the satellites- both natural and artificial - revolve around the planets due to the gravitational pull of the planets. Like the planets , the satellites too do not have light of their own. They shine in space and become visible to us because
they reflect the light of the sun falling on them . 121.How artificial satellites are positioned in their orbits in the sky?
Artificial satellites are carried into space and placed in there orbits with the help of rockets. They are so positioned that the earth's gravity keeps them circling the earth without drifting away. The
distance of the artificial satellites from the earth and their speed of revolution can be adjusted according to our needs . 479
122. How artificial satellites are worked?
Artificial satellites are loaded with a large variety of instruments and equipment depending upon the purpose for which they have been launched. For example, they may be carrying cameras, infrared sensors, telescopes and sound and picture relaying machines that continuously send information to the earth. Computers on the earth receive and process the signals. Solar cells and solar panels provide the electric power needed to run the instruments year after year.
123. What are the applications of remote sensing satellites? Remote Sensing satellites collect information and scan the earth very
closely with the cameras and infrared sensors while orbiting high above the earth. They can see the details on the earth up to a fraction of a
metre quite precisely. 124. What are the applications of Communication satellites? Communication satellites can send radio and television programs around the world. These are indispensable for telephone calls and internet. 480
125. What are the application of Weather forecasting satellites?
Weather forecasting satellites watch weather (rainfall, snowfall and clouds) and can warn people about floods, cyclones and hurricanes. They also inform us about pollution of air and water.
126.What are the application of Navigation satellites ? Navigation satellites can guide cars , ships and aircraft , and help us
(if we get lost) even if it is cloudy. 127.What are the application of Spy satellites? Spy satellites are used by armies to watch troop movements, movement of ships, aircraft an missile launches. 128. What are the application of Space satellites?
Space satellites , equipped with huge telescopes , orbit the earth, they watch space , other planets , stars and galaxies.
129. What are the other applications of satellites? There are numerous other applications such as surveying the natural resources , crops , fishing zones so on. 481
130. How we identify north direction?
We can find our north direction with the help of a magnetic compass or by observing the rising sun. 131. How one can identify Polar star?
Look at the night sky along the north direction and tilt the eye above the horizon through an angle nearly equal to the latitude of
the place. Now it is to be tried to locate a star of average brightness which has no other visible stars in its neighborhood. This is the Pole star.
The location Pole star can be confirmed by looking for the
constellation Ursa Minor in its neighbourhood. The constellation has seven stars( Laghu Saptarishi) and looks like a kite having a thread
at its corner. The pole star is at the end of the thread. The constellation Ursa Major is also in the neighbourhood of the pole
star. Ursa Major has 7 stars in it and the Pole star lies on the joing 2 stars (called pointers) of this constellation
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