Science at key stage 3 (Year 7)
Unit 7J: Electrical circuits
Section 6: b. How can we explain what happens in electrical circuits?
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Objectives |
| Children should learn: |
- to construct parallel circuits
- to predict the current in branches of a parallel circuit
- to identify patterns in measurements
- to apply the water model or a similar model to parallel circuits
- to consider the limitations of a model
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Activities |
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Outcomes |
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Children: |
- Ask pupils to set up parallel arrangements of bulbs and use a model to explain why bulbs connected in parallel remain at the same brightness.
- Show circuit diagrams of simple parallel circuits with identical components in each branch. Ask them to predict current readings and to check this by measurement. Follow up with a demonstration to confirm that the sum of the current flowing in each branch is the same as that flowing in the main circuit. This offers more evidence of current conservation.
- Demonstrate a water circuit, or other model, to show the effect of resistance in parallel. Ask pupils to think of ways in which electricity is not like water,
eg when the wire breaks it doesn't run out. Invite pupils to think of other models, and to discuss their strengths and weaknesses.
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- explain how connecting bulbs in parallel allows each to shine equally brightly
- predict and explain measurements of current in different parts of parallel circuits
- explain these observations using a model
- identify strengths and weaknesses of a model for electricity
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Points to note |
- Many pupils will be surprised that both bulbs are of equal brightness when two in series are much dimmer. Distance from a battery is often seen as important and pupils might suggest that a bulb is dimmer because it is 'further from the battery'. Circuit boards are useful for laying out parallel circuits clearly, but they often have additional resistance at connections in the circuit - so beware. Variations in apparently identical bulbs can lead to anomalous results. It may help to swap the bulbs round.
- The nature and behaviour of electrons and charge is not required until key stage 4. A flow model is adequate to explain all the work covered in key stage 3.
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This unit is divided into sections. Each section contains a sequence of
activities with related objectives and outcomes. You can view this unit by
moving through the sections or print/download the whole unit.
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