Science at key stage 3    (Year 9)

• Remind pupils of their experience of energy transfers and transformations in years 7 and 8 with demonstrations of 'useful changes', eg working a model steam engine, a spring-driven clock, eating food. Help pupils associate the presence of energy with the different situations in the demonstrations, eg steam-engine fuel, flame, hot water, movement, and to use the terms 'kinetic', 'potential', 'chemical energy', 'heat', 'light' and 'sound' as ways of describing energy in such situations.
• Ask pupils to explore a circus of toys and devices that work by transferring and/or transforming energy. Ask pupils to identify the source of energy and the use to which it is put. Include a range of electrical toys and devices, eg
• battery-operated and clockwork/spring-operated vehicles
• yo-yo (if possible one that lights up at maximum speed)
• battery-operated and manually operated fans
• electromagnet for lifting
• electric bell or buzzer
• solar-powered calculator or motor
• low-voltage heater that is set to get warm, not hot, to the touch
• toys that feature light-emitting diodes (LEDs)
• simple control circuit, eg one that sounds a buzzer when a light sensor is covered

• Elicit from pupils' observations the conclusion that electrical energy is a convenient way to do many useful things. Recall pupils' year 7 work on fuels as energy stores and elicit other ways that energy can be stored, eg compressed spring - potential; flywheel - kinetic; battery - chemical. Contrast this with electricity, which cannot be stored.

• Review pupils' understanding of simple circuits - the requirements for current to flow, and the effect of the number of cells or components in series and parallel circuits (unit 7J 'Electrical circuits') - by using quiz cards that describe real circuits with faults and by measuring currents in circuits.

• Ask pupils to construct simple series circuits incorporating several components and batteries or power supplies of different voltages. Help them to connect the voltmeter across each component in turn, without breaking the circuit. Individual readings can be seen to add to the total voltage. Encourage pupils to associate large voltage changes with large energy transfers by the components, eg bright bulbs.

• Introduce a model to associate energy transfer with voltage, eg the 'almost Monopoly' or 'pocket money' analogy, where pupils are given money that has to be spent around the circuit before they can return. Pupils are the current, the cell is the source of the money ('GO'), which is the energy. The cells or voltage permit them to move. If they go through more cells, they pick up more money; and as they go round the circuit, they have to pay out equal amounts per device (assuming identical devices). As an analogy of resistance, money could be paid out in proportion to 'number of hotels', or use a similar rule from Monopoly. Note the shortcoming in the analogy - in Monopoly circuits all the money does not have to be spent.
• An alternative model is the 'up-and-down' ski-lift. Chairs are the 'current/charge' which the 'voltage' of the motor causes to move (flow). Skiers are the 'energy', climbing on at the motor-house and getting off at suitable places ('devices') around the ski-lift circuit.

• Show the inside of a dry cell. Establish that there is a chemical change when a battery/cell produces a current. Associate the energy of the chemical change with input to a circuit.
• Ask pupils to plan an investigation into how to make a cell from a fruit or vegetable to produce the highest voltage, eg the performance of a particular fruit with a range of electrode sizes, separations or metal combinations, the relative effectiveness of different fruit. If appropriate, link to work on the relative reactivity of different metals.

• Use the Electricity Council video Electric graffiti, or other secondary sources, to identify the hazards of high voltages and associate these with the transfer of large amounts of energy, eg lightning, overhead and power lines on railway tracks.

• Discuss the household mains supply at 230V and how appliances, eg television, computer, run from this, using pupils' experiences. Show an electricity bill and ask pupils What are the units used? Remind them that current is not used, but energy is. Show (pictures of) a household electricity meter.
• Demonstrate the energy used by a range of electrical devices, eg for heating, lighting, (over a fixed period of time for comparison purposes) using a joulemeter/datalogger. Show how these comparisons relate to the power ratings on devices.
• Ask pupils if they think people are aware of these differences, eg Do parents talk about the waste of money of 'leaving the TV on all evening'? Ask how they could find evidence to check such comments, and then devise a parents' guide entitled 'How to get your children to save energy by switching the right things off'. This could be supported by putting examples of household appliances on cards and asking pupils to arrange them in order of energy consumption. Compare the amount of energy used by a range of devices in the home or school, as shown by the power rating noted on the devices, eg light bulbs, fridges, microwaves, heaters, cookers, computers, televisions.

• Ask pupils to summarise ways in which electricity can transfer and transform energy to provide people with useful facilities - as a list or a concept map.

• Elicit ideas about where mains electricity comes from. Trace the story back to a power station.
• Demonstrate a bicycle dynamo or simple generator. Show how increasing (energy) input will increase (energy) output.
• Use a small motor as an electrical generator, or make one from a kit, and test its output using a sensitive meter. Possibly drive it using a windmill to simulate wind turbines. Plan a visit, show a video or use information resources such as a CD-ROM to introduce pupils to the generation of electricity in power stations. Contrast the scale of the operation with laboratory generators, and consider the fuels used.

• Ask pupils to use secondary sources to compare the impact on the environment of various forms of electrical generation. This may be done in groups, with each group reporting back its findings. This may include both renewable and non-renewable resources as well as the more complex issue of nuclear waste.

• Recall earlier work on energy devices and on burning fuels. Review the paradox that although electricity is clean and safe to use, its generation can have a big environmental impact. Introduce the idea of dissipation of waste energy as an inevitable consequence of many energy transfers; refer to cooling towers at power stations.
• Broaden the issue to looking at use of energy in different ways, eg ask pupils to consider how environmentally friendly electric cars really are. (Although electric motors are three times as efficient as internal combustion engines, the electricity has to be generated first.) Compare battery-powered cars (recharged at the mains) with fuel-cell powered models. Compare the energy required to make a car with the energy needed to run it (ratio is approximately 10:1). Is the real issue about replacing old, inefficient cars with new, more energy-conserving ones?
• Use questions to discuss with pupils the difference between tungsten-filament light bulbs and 'energy-saver' bulbs, eg a 20W energy-saver lamp is said to be equivalent to a 100W filament lamp. Can this be supported? What happens to the other 80W from the filament lamp? (Feel the heat - carefully.)
• Provide information about these lamps, eg advertising material, and ask pupils to work out whether the purchase of energy-saver bulbs is cost effective.

• Introduce the principle of the conservation of energy, using a range of examples to make the distinction between energy that is useful and energy that is dissipated and not useful. Ask pupils to draw flow diagrams, eg Sankey-type, to show energy transfers in everyday situations, eg home heating, transport, use of insulation.

• Draw flow diagrams identifying energy transfers and transformations in a wider range of situations, eg the devices studied earlier in the unit, home insulation.
• Encourage pupils to use games to review connections, eg
• chain games from the numeracy strategy
• 'energy consequences' (first line - describe an event, second line - describe an energy transformation. When the text is revealed pupils have to explain whether the consequences are possible or not)
• 'energy dominoes' (prepare a set of cards with a question about an aspect of energy on one half and an unrelated answer on the other. One pupil asks a question and the pupil who has the answer reads it aloud, then asks his/her question)
• The opportunity could be taken to revise related topics from previous years, eg conduction and convection, covered in unit 8I 'Heating and cooling'.