Preview: Cambridge Lower Secondary Science Teacher Guide 9

Cambridge Lower Secondary

Science STAGE 9: TEACHER’S GUIDE

Lucy Hawkins, Fran Eardley, Stuart Lloyd, Gemma Young, Sheila Tarpey 244408 Checkpoint Science_Title page_TG9.indd 1

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Contents

Downloads of editable learning episodes, worksheets, practical notes and answers are available at www.collins.co.uk/CambridgeInternationalDownloads.

Introduction Mapping document

5 9

Chapter 1 ● Photosynthesis and plant growth Chapter overview 1.1 The photosynthesis equation

23 25

1.2 Water and mineral salts Checking students’ progress

34 41

Chapter 2 ● Sexual reproduction in flowering plants Chapter overview 2.1 Flowers and pollination

42 44

2.2 Seed dispersal Checking students’ progress

52 57

58 60 65

3.3 Populations and extinction 68 3.4 Human influences on the environment 72 Checking students’ progress 76

77 79 83

4.3 Selective breeding 4.4 Natural selection Checking students’ progress

86 89 91

92 93

5.2 Trends in the Periodic Table Checking students’ progress

96 99

Chapter 3 ● Ecology Chapter overview 3.1 Food webs and energy flow 3.2 Adaptation and survival Chapter 4 ● Variation and inheritance Chapter overview 4.1 Using classification keys 4.2 Genes and DNA Chapter 5 ● The Periodic Table Chapter overview 5.1 Structure of an atom Chapter 6 ● Preparing salts Chapter overview 6.1 Reactions with acids

100 101

6.2 Methods for making salts Checking students’ progress

105 109

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

110 112 118

7.3 Rates of reaction Checking students’ progress

122 129

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

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130 132

8.3 Energy transfers in changes of state 142 Checking students’ progress 145

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Chapter 9 ● Electrostatics and electric currents Chapter overview 9.1 Charge and electrostatics 9.2 Series and parallel circuits

146 148 153

9.3 Explaining current in circuits 9.4 Voltage Checking students’ progress

157 160 163

164 166 170

10.3 Pressure in gases and liquids 10.4 Density Checking students’ progress

173 177 181

182 184 188

11.3 Conduction, convection and radiation Checking students’ progress

191 200

Chapter 10 ● Moments, pressure and density Chapter overview 10.1 Turning effect of a force 10.2 Pressure on an area Chapter 11 ● Energy Chapter overview 11.1 Energy resources 11.2 The world’s energy needs Planning guide

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Chapter 9

Electrostatics and electric currents

Chapter overview In this chapter students will learn about electric charge – how it builds up and some effects of static electricity. They will investigate the flow of current in series and parallel circuits and how cells and batteries work.

Stage 9

Cambridge Lower Secondary Physics

This builds on the previous work on types of energy and energy transfers.

Topic title

Student’s Book pages

Number of 40minute periods

Overall objectives

Scientific enquiry focus

9.1 Charge and electrostatics

166–171

2–3

Describe electrostatics and the concept of charge

Make observations and measurements Interpret results using scientific knowledge and understanding

9.2 Series and parallel circuits

172–175

3

Interpret and draw simple series and parallel circuits Measure current using an ammeter Explain how current varies in series and parallel circuits

Use a range of materials and equipment and control risk Draw conclusions

9.3 Explaining current in circuits

176–178

2

Model and explain how common components affect current Investigate the effect of changing the length of a wire on its resistance

Assess and control risk Choose the best way to present results Draw conclusions

9.4 Voltage

179–182

2

Explain how a cell works Investigate ways of producing the maximum voltage from a cell

Select ideas and produce plans for testing based on previous knowledge, understanding and research Choose the best way to present results

End of chapter review

183–185

1

Check students’ progress

Background science Electrostatic charging happens when electrons are rubbed from one material to another. The material gaining electrons becomes negative and the one losing electrons becomes positive.

Like charges repel. Unlike charges attract.

The Van der Graaff generator produces a build-up of charge using friction.

Current is a flow of charge, carried by electrons. The electrons flow from the negative of a cell, round the circuit to the positive of the cell. Conventional current is described as flowing from positive to negative. At this level it is best to avoid mentioning the direction of flow as it can cause confusion.

A series circuit is made of a single loop. The current is the same all round the circuit. The electrons lose energy as they flow round the circuit, but this doesn’t affect current. A parallel circuit has two or more loops. The current splits when it reaches a junction but the current flowing into a junction is the same as the current flowing out.

Current is measured using an ammeter which must be placed in series with the component you wish to measure the current through.

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The current flowing in a circuit depends on the voltage supplied by the battery and on the resistance of the components in the circuit. The greater the resistance, the lower the current. Increasing the length of a wire will increase its resistance.

Other components affect current flow – a diode will only let current flow in one direction and a variety of switches can turn current on and off.

A cell or battery supplies voltage. This is best described in terms of giving the electrons the energy needed to move round the circuit.

The voltage of a cell or battery is measured using a voltmeter which should be connected in parallel across the cell or battery. When cells are connected in series the total voltage is the sum of the voltages of the cells.

When two different metals are placed in an acid substance, there will be a voltage across them. This makes a simple cell.

Stage 9

Cambridge Lower Secondary Physics

The lightning shown in the chapter opening page occurs when friction within clouds builds up an electrostatic charge so great that the air temporarily conducts electricity, allowing this charge to flow to earth.

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9.1

Charge and electrostatics

Topic overview Student’s Book

Downloadable material

9.1a

Starting point

Page 166 Starting point table

9.1b

Charging by friction In this activity pupils consolidate their knowledge of atomic structure and consider how charges can be separated

Pages 166–167 Questions 1–3 Activity 9.1

Questions 1–2

Practical notes 9.1b

9.1c

Positive and negative charge This practical activity allows pupils to investigate attraction and repulsion due to electrostatic charges

Pages 167–168 Questions 4–7 Activity 9.2

Questions 3–6

Practical notes 9.1c Worksheet 9.1c

9.1d

The electrostatic generator This spectacular demonstration shows the power of static electricity

Pages 168–169 Questions 8–10 Activity 9.3

Questions 7–9

Practical notes 9.1d

9.1e

Applying ideas – lightning The Van der Graaff generator is linked to the natural phenomenon of lightning

Page 169

Questions 10–12

9.1f

Uses and dangers of electrostatics Some practical examples of uses and dangers are described

Pages 169–171 Questions 11–13

Topic learning objectives • 9Pm1: Describe electrostatics and the concept of charge, • • •

including digital sensors 9Eo3: Make observations and measurements 9Ec4: Draw conclusions 9Eo2: Use a range of materials and equipment and control risks

•

9Eo4: Choose the best way to present results

•

9Ep4: Select ideas and produce plans for testing based on previous knowledge, understanding and research 9Ep7: Decide which measurements and observations are necessary and what equipment to use

•

Common misunderstandings • Students may describe positive charging as occurring when an object gains positive charge. Remind them that •

protons are in the nucleus and cannot move from the atom. Positive charging is the result of losing negative charge.

Students may assume that if objects attract, they must be oppositely charged. However it could be that one is uncharged. Compare this with magnets where similar rules apply.

9.1a Starting point Review what students have learned in Chemistry about atomic structure and the positions and charges of neutrons, protons and electrons.

Stage 9

Cambridge Lower Secondary Physics

Workbook

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9.1b Charging by friction Learning outcomes • To describe electrostatics using the idea of charge • To investigate how charges affect each other Scientific enquiry outcomes • Make observations and measurements Glossary words electron, electrostatic, insulator

Resource preparation For Activity 9.1: balloons, polythene and acetate rods or plastic ruler, cloths, tissue paper.

Practical notes 9.1b

Teaching and learning ideas • Ask students to sketch a picture of an atom. Get them to pair up then form groups of four, at each stage sharing and • • •

refining their diagrams. Ask a few pairs to show their diagrams and establish a clear understanding of the nuclear model of the atom. The key things they need to know are that positive charge is in the nucleus and does not move; negative charge is carried by the electrons which can easily be lost or gained.

Demonstrate some of the effects of charging by friction, for example, rub a balloon and show it can stick to the wall.

Students can then investigate charging objects and using them to attract light objects. See Activity 9.1 on Student’s Book page 167 and Practical notes 9.1b. This can include picking up small pieces of paper (tissue paper is best), sticking balloons to walls and attracting a slow stream of water to a charged rod or plastic ruler.

Students can demonstrate what they have done to other groups and record their findings using words or diagrams.

Differentiation Students could review the work they have done earlier in the Chemistry sections on atomic structure, and develop electronic diagrams or cut-out diagrams of the particles in an atom to show how electrons are free to move but protons and neutrons are not.

Homework suggestions Extension ideas Students could investigate how the strength of the electric field (attraction) can be increased. They should consider how they might move more charges and so increase the attraction. They should also suggest how they could measure this (e.g. by counting the numbers of small pieces of paper they can pick up).

9.1c Positive and negative charge Learning outcomes • To describe electrostatics using the idea of charge • To investigate how charges affect each other Scientific enquiry outcomes • Make observations and measurements Glossary words

© HarperCollinsPublishers 2018

Stage 9

electron, electrostatic, insulator

Cambridge Lower Secondary Physics

Students should complete Workbook questions 1−2 on this topic.

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Resource preparation For Activity 9.2: polythene and acetate rods, cloths.

Practical notes 9.1c Worksheet 9.1c

Teaching and learning ideas • Refer back to the model of the atom. Explain that only negative charges can move because of their location at the • • • • •

outside of the atom.

Complete Worksheet 9.1c. Spend time ensuring students understand how positive and negative charging occurs.

Explain that in conductors this effect is not noticed because charges will flow and balance out.

Explain to pupils that whether an insulator becomes positive or negative depends on what it is made of (they are not required to know which materials charge which way). Tell them that polythene becomes negative and acetate positive. They will use this to investigate how the charges affect each other.

Demonstrate to the pupils how to charge and suspend a rod. Talk about how to avoid discharging the rod (do not touch the rubbed end while hanging the rod in the paper stirrup). Discuss why different cloths should be used for the different rods (cloths become charged too).

Allow the students to carry out the investigation and draw conclusions. Refer to Activity 9.2 on Student’s Book page 167 and Practical notes 9.1c.

Discuss any anomalous results. In particular, students may get attraction between identical rods. This is likely to be because one of the rods has not been charged, or has lost its charge when put down or held. Any charged rod will attract an uncharged one. Link this to the idea that only repulsion can give proof of charging.

Differentiation The Worksheet provides support for students as the first diagram can be roughly copied in order to make the second diagram.

Homework suggestions Students should complete Workbook questions 3–6 on this topic.

Extension ideas Students could select other materials and predict whether or not they might be charged, then design tests of their predictions, as well as write explanations of the results they obtain.

Learning outcomes • To describe electrostatics using the idea of charge • To investigate how charges affect each other Scientific enquiry outcomes • Make and record observations • Interpret observations using scientific knowledge and understanding Glossary words electron, electrostatic, insulator

Resource preparation For Activity 9.3: Van de Graaff generator, wooden ruler, plane mirror, polythene sheet, bubble blowing kit, foil cases.

See Practical notes 9.1d for details of safe and entertaining use of the Van der Graaff generator. This is a potentially hazardous demonstration but is one which students will not forget. The demonstration should be practised beforehand.

Practical notes 9.1d

Stage 9

Cambridge Lower Secondary Physics

9.1d The electrostatic generator

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Teaching and learning ideas • Always begin by emphasising safety. Students are not allowed to touch the generator without permission and should • • • • • •

not touch another student who is being charged by it. Establish that although it can give a shock, this is painful rather than dangerous. Be clear that only volunteers will get a shock.

Talk through the construction of the generator, linking this to prior learning – friction between the belt and dome builds up charge. The dome is electrically insulated so charge can build up on it.

Begin with demonstrations showing attraction and repulsion. Uncharged bubbles are attracted to the dome. Metal cake cases placed in a pile on the dome become charged and so repel each other causing them to fly off the dome.

Charge a volunteer student and watch as their hair stands on end due to repulsion between the hairs.

Demonstrate discharge via sparks. This can be a spark from the dome to the smaller dome, or from a charged student to an uncharged peer. Make the link to lightning.

Students who do not wish to get a shock on discharge can allow charge to flow away slowly down a wooden metre ruler.

Students can answer questions 8–10 from the Student’s Book (page 169) to check their understanding of the generator. It is also useful to discuss real life situations where they have experienced electrostatic charging. Use questioning to elicit the common factors – friction between insulators.

Homework suggestions Students should complete Workbook questions 7–9 on this topic.

Extension ideas Students could develop models or explanations for more everyday situations in which charging and discharging can occur; this may include plastic slides as in the Student’s Book photograph, trampolines or escalators.

9.1e Applying ideas – lightning Learning outcomes • To describe electrostatics using the idea of charge • To investigate how charges affect each other Glossary word electrostatic

•

on the generator.

Workbook questions 10–12 go into further applications of electrostatics; these could be discussed in class or set as research activities for students.

Differentiation Video explanations of how charge builds up in clouds and on the ground, and how a lightning strike occurs, can be useful for students to understand the stages of the process.

Homework suggestions Students should complete Workbook question 12 on this topic.

Extension ideas

Stage 9

Students could use the stages described in Workbook question 12 to develop models of how the electric charge is transferred and to develop a set of safety instructions for anyone caught outside when a thunderstorm occurs.

Cambridge Lower Secondary Physics

Teaching and learning ideas • Refer back to the photograph at the start of the chapter. Compare the lightning flash with the spark they have seen

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9.1f Uses and dangers of electrostatics Learning outcomes • To describe electrostatics using the idea of charge • To investigate how charges affect each other Teaching and learning ideas • This is an opportunity for students to carry out research and present their findings to the class.

• Begin by discussing dangers – students will recognise why sparks can cause danger in situations where there could

be a build-up of flammable materials. They can be introduced to uses using the examples in the Student’s Book, and any other situations which are relevant, such as photocopiers, and charging metal and paint to improve the efficiency of spray painting. Students can then carry out their own research and present their findings.

Homework suggestions Students should complete questions 11–13 from the Student’s Book (page 170).

Extension ideas

Stage 9

Cambridge Lower Secondary Physics

Students could use the stages described in Workbook questions 10 and 11 to develop models of how the electric charge is transferred and sustained in order for the applications to work.

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