Previous: Cambridge Lower Secondary Science Student Book 9

Cambridge Lower Secondary

Science STAGE 9: STUDENT’S BOOK

Lucy Hawkins, Fran Eardley, Stuart Lloyd, Gemma Young, Sheila Tarpey

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Contents How to use this book

v

Chapter 1 • Photosynthesis and plant growth 1.1 The photosynthesis equation 1.2 Water and mineral salts

3 10

End of chapter review

17

Chapter 2 • Sexual reproduction in flowering plants 2.1 Flowers and pollination 2.2 Seed dispersal

22 29

End of chapter review

35

38 45 50

3.4 Human influences on the environment End of chapter review

55 61

65 71 76

4.4 Natural selection End of chapter review End of stage review

80 86 89

96 102

End of chapter review

110

113 120

End of chapter review

125

Chapter 3 • Ecology 3.1 Food webs and energy flow 3.2 Adaptation and survival 3.3 Populations and extinction

Chapter 4 • Variation and inheritance 4.1 Using classification keys 4.2 Genes and DNA 4.3 Selective breeding Chapter 5 • The Periodic Table 5.1 Structure of an atom 5.2 Trends in the Periodic Table Chapter 6 • Preparing salts 6.1 Reactions with acids 6.2 Methods for making salts

Chapter 7 • Reactivity and rates of reaction 7.1 The reactivity series 7.2 Displacement reactions

128 134

7.3 Rates of reaction End of chapter review

137 144

iii

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Chapter 8 • Energy transfers in chemistry 8.1 Temperature changes in reactions 8.2 Exothermic and endothermic processes

147 151

8.3 Energy transfers in changes of state 157 End of chapter review 159 End of stage review 162

Chapter 9 • Electrostatics and electric currents 9.1 Charge and electrostatics 9.2 Series and parallel circuits 9.3 Explaining current in circuits

166 172 176

9.4 Voltage End of chapter review

179 183

Chapter 10 • Moments, pressure and density 10.1 Turning effect of a force 10.2 Pressure on an area 10.3 Pressure in gases and liquids

187 193 198

10.4 Density End of chapter review

202 207

11.1 Energy resources 11.2 The world’s energy needs 11.3 Conduction, convection and radiation

211 221

End of chapter review End of stage review

236 238

Periodic Table Circuit symbols Glossary Index Acknowledgements

240 241 242 248 254

Chapter 11 • Energy

228

iv

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9 Chapter 9 Electrostatics and electric currents

What’s it all about?

Electricity can kill, but without it our lives would be very different. Why does lightning happen? Why does rubbing a balloon make it stick to the wall? What makes a lamp light up?

How can we make circuits to light our homes?

Understanding what electric charge is and how it behaves will help you to answer these and many more questions.

You will learn about: • What electric charge is and how objects become charged • How charges affect each other • How electrostatic charges can be useful or dangerous • How to build and draw electric circuits • The things that affect the size of an electric current • How current behaves in different circuits • How to measure current and voltage You will build your skills in: • Choosing apparatus • Deciding which measurements to take • Assessing any hazards and working safely in experiments • Obtaining reliable results • Making conclusions using scientific knowledge and understanding Electrostatics and electric currents

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Chapter 9 . Topic 1

Learning outcomes • To describe electrostatics using the idea of charge • To investigate how charges affect each other

Charge and electrostatics Starting point You should know that…

You should be able to…

Everything is made of tiny particles called atoms

Make and record observations

Some materials, called conductors, let electricity through; others, called insulators, don’t

Identify patterns in your observations

Metals are conductors – most non-metals are insulators

Interpret your results using scientific knowledge and understanding

Charging by friction electron

nucleus

9.1 The structure of an atom.

Everything is made up of atoms. All atoms have positive charge and negative charge in them. The positive charge is in the nucleus in the centre of the atom.

The negative charge is on the electrons, which move round the outside of the nucleus. Friction can make some electrons move from one object to another. When this happens we say the object has an electrostatic charge.

166

Key terms electron: subatomic particle with negative charge.

1

Where is the positive charge in an atom?

2

What moves from one atom to another when insulators are rubbed?

electrostatic charge: charge on an insulator that has gained or lost electrons.

3

Suggest why friction can move negative electrons, but not positive charge.

insulator: material that doesn’t let electric charge move through it.

Electrostatics and electric currents

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9 .1 Activity 9.1: Investigating charging You will need a plastic ruler, a balloon, a dry cloth and some tiny pieces of tissue paper.

A1 Charge the ruler by rubbing it. Hold it close to the pieces of tissue paper and record what happens.

A2 Blow up the balloon and rub it. Notice how the charge attracts things – try picking up paper, sticking the balloon to the wall and bending a flow of water.

A3 Record your observations.

9.2 A charged balloon can bend water.

Positive and negative charge Gaining electrons makes an object negatively charged.

Losing electrons makes it positively charged. balloon

+ + + + + + sweater

9.4 Electrons move to the balloon from the wool sweater.

9.3 When this balloon is rubbed against the sweater, electrons move to the balloon from the sweater.

Some materials gain electrons when rubbed. Polythene will gain electrons and become negative. Other materials lose electrons. Acetate will lose electrons and become positive.

Activity 9.2: Investigating how charged objects affect each other Plan how you could investigate how positive and negative charges affect each other.

A1 How will you suspend the insulators so they can move?

A2 How will you record your results?

A3 Write a conclusion about how charges affect each other.

– – –– –– – – –– – –

– – –– – –– –– – – –

9.5 These balloons are both negatively charged and they repel each other.

Charge and electrostatics

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4

Name the two different types of charge.

5

What happens if a charged object is brought close to an uncharged one?

6

What happens if two objects with the same charge are brought together?

7

Two students bring a positively charged rod close to another rod. The rods move together. One student says that the second rod must be negatively charged – the other says the opposite. Who is right?

The electrostatic generator

9.6 This machine is used to investigate electrostatic forces.

A motor turns the belt causing friction between the belt and the dome. The belt collects electrons from the dome, leaving the dome at the top positively charged.

9.7 Anything touching the dome will also become positively charged.

Activity 9.3: The electrostatic generator Take great care when using an electrostatic generator.

Your teacher may let you try some of these activities.

• Blow some soap bubbles over the dome.

• Put a stack of small foil cases on the top of the dome.

• Stand on a polythene sheet and place your hand on the dome.

A1 Record your observations and explain what happens using the words ‘attract’ and ‘repel’.

168

Electrostatics and electric currents

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9 .1 8

Why does the dome of the electrostatic generator become charged?

9

Why does your hair stand on end when you are in contact with the dome?

10

Look at figure 9.8. Explain why this child’s hair is standing on end as she comes down the plastic slide. What will happen to her hair when she reaches the ground?

9.8

Applying ideas: lightning If a smaller metal dome is brought close to the van de Graaff generator, a spark passes between the domes. This is because there is so much energy that the air allows charge to pass through it. This is what happens when storm clouds become charged. The spark is a lightning flash.

9.9 A lightning flash.

Uses and dangers of electrostatics A plane can build up a lot of charge as it lands. This could cause a dangerous spark when the plane is fuelled. A wire is used to discharge the plane to make sure this doesn’t happen.

Digital cameras contain a device called a CCD (chargecoupled device). It uses charges to detect light and create an image.

9.10 A plane being refuelled – you can see the wire used to discharge the plane.

9.11 The CCD device on a camera.

Charge and electrostatics

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Electrostatic attraction can be used to decrease the amount of pollution from factory chimneys. waste gases without smoke particles

positively charged collecting plate

chimney wall

negatively charged metal grid

waste gases containing smoke particles

9.12 A system for removing waste particles from a chimney.

The smoke particles pass through the grid and pick up electrons – this makes them negative. Higher up the chimney they are attracted to the positively charged plates.

11

Why can a charge build up on a plane?

12

Modern digital cameras use a CCD to form and store images. What did cameras use before this?

13

Does removing the smoke particles from the waste coming out of a chimney make the waste gases completely harmless?

Central Africa is the lightning capital of the world!

NASA has recorded every lightning bolt to hit the Earth.

They are more frequent over land than over the oceans, and are most frequent near the equator. This is because solid land heats up quickly, heating the air above it. This makes the air move more, causing friction and charging in the clouds, which causes lightning.

170

Electrostatics and electric currents

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9 .1

Lightning Flash Rate (flashes per km2 per year) 0.1

75.0

150.0

9.13 The lighter areas are where lightning strikes are most common.

Key facts:

Check your skills progress:

✔ All atoms contain positive charge in the nucleus and negative charge in the surrounding electrons.

I can describe how friction causes electrostatic charging.

✔ Electrons can be lost or gained by friction. ✔ Insulators may gain a net overall charge because the charges cannot move within the insulating material.

I can describe everyday effects of electrostatic charging.

I can predict whether objects will attract or repel using my knowledge of like and unlike charges.

✔ Like charges repel. Unlike charges attract.

Charge and electrostatics

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