O-LevelPhysicsElectricity5054/21 · May/June 2017 · Q67 Marks

Fig. 6.1 shows a 240 V a.c. mains supply connected to a television and two lamps. [Figure 6.1] In normal operation, the power supplied to each lamp is 40 W and the power supplied to the television is 120 W.

(a)(i)Calculate, in normal operation, the total power supplied,[1]
(a)(ii)the total number of kilowatt-hours (kWh) of energy supplied to the circuit in 3.0 hours,[2]
(a)(iii)the current in each lamp.[2]
(b)Explain why the switches are placed in the live wire and not in the neutral wire.[2]

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Mark scheme

Marking points from the official mark scheme (May/June 2017). The mark or mark type is shown in brackets.

[1] 200 W
[1] power × time or any numerical value of power × 3
[1] 0.6(0)
[1] (I =) P/V algebraic or numerical
[1] 0.17 A
[1] (if in neutral) rest of circuit / lamps / television not live / still high voltage / still 240 V or live has high voltage / 240 V / can cause shock
[1] (if in neutral) when (switched) off circuit / lamps / television not live / still high voltage / still 240 V

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