Science at key stage 3 (Year 7)
Unit 7J: Electrical circuits
Section 8: b. What kinds of circuits are useful and what are the hazards?
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Objectives |
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- that electrical energy from the battery is transformed by a fuse to light and heat; this can cause it to melt
- to plan safe procedures, recognising hazards
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Activities |
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Outcomes |
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Children: |
- Show the pupils a circuit with three cells, ammeter and variable resistor in series with a short length of steel wool. Reduce the resistance and observe that as the current increases, the steel wool gets hot and then fuses (melts).
- Provide lengths of suitably current-rated fuse wire and ask pupils to plan and then test them to (planned) destruction using low-voltage power supplies and a bulb in a new circuit. Discuss the reasons for the use of fuses, including the resettable ones in modern fuse boxes and the cut-outs in laboratory power supplies.
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- explain how a fuse protects a circuit
- work safely
- compare predictions with observations,
eg current to 'blow' a fuse
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Points to note |
- Resettable cut-outs are not fuses; they are coils which use magnetic effects to detect current flows, and are better described as circuit breakers.
Safety
- choose fuse wire that will blow at a current lower than the bulbs in the circuit
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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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