O-LevelPhysicsElectricity5054/22 · Oct/Nov 2022 · Q58 Marks

The power supply in a circuit is made from several cells, each with the same electromotive force (e.m.f.). The cells are connected in parallel.

(a)Explain what is meant by 'electromotive force'.[2]
(b)State one advantage of using several cells in parallel rather than a single cell as the power supply.[1]
(c)(i)The power supply is connected in series to a resistor of resistance 4000 Ω and a thermistor. There is a voltmeter in parallel with the resistor. Fig. 5.1 is the circuit diagram. [Figure 5.1] The temperature of the thermistor increases. Explain what happens to the reading on the voltmeter.[3]
(c)(ii)The e.m.f. of the power supply is 1.5 V. Calculate the reading on the voltmeter when the resistance of the thermistor is 8000 Ω.[2]

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Mark scheme

Marking points from the official mark scheme (Oct/Nov 2022). The mark or mark type is shown in brackets.

[B1] energy / work done per unit charge or (energy work done) / (charge charge)
[B1] property of a source / cell / battery / power supply or energy used driving charge around a (complete) circuit or energy transferred to electrical energy
[B1] it lasts for a longer time or more (electrical) energy available or power
[B1] supply still functions if one cell fails / runs flat or can replace one cell without stopping circuit / stopping current
[B1] resistance (of thermistor / circuit) decreases c.a.o.
[B1] current change or voltage change across thermistor matching the change in the resistance of the resistor
[B1] reading of voltmeter increases c.a.o.
[C1] (V₁ =) V₀ × R₁ / R₀ or 1.5 × 4000 / (4000 + 8000) or 1.5 × 4000 / 12 000 or I = V/ R or 1.5 × 8000 / (4000 + 8000) or I =1.5/12 000 or 0.125 mA
[A1] 0.50 V

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