O-LevelPhysicsElectricity5054/22 · May/June 2015 · Q75 Marks
An electric hairdryer and an electric heater are connected to the mains supply, as shown in Fig. 7.1. [Figure 7.1] The cable from the heater to the mains supply has a live, a neutral and an earth wire.
- (a)State the purpose of the neutral wire.[1]
- (b)The live wire in the electric heater touches the outer metal case. Explain how the earth and the fuse together protect the user from electric shock.[2]
- (c)The hairdryer does not have an earth wire. Explain why this hairdryer is still safe to use.[1]
- (d)In some modern homes, circuit breakers are used instead of fuses. Suggest one advantage of using a circuit breaker rather than a fuse.[1]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme (May/June 2015). The mark or mark type is shown in brackets.
- [1] (a) to provide a complete circuit (with live)
- or to pass current back to mains
- or provide a return path for the current
- [1] (b) current/charge/electrons flow to earth/earth wire/ground (when live touches
- case)
- [1] (b) fuse melts/blows and disconnects circuit/cuts live/stops current
- [1] (c) doubly insulated
- or case/body made of plastic/insulator/not made of metal
- or user cannot touch metal
- [1] (d) (circuit breaker)
- • turns off/acts fast(er)
- • can be reset
- • easy to see it has tripped/switched
- • can detect small difference between live and neutral currents / small
- (leakage) current to earth
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