Physics 5054 · O Level · Circuit diagrams and circuit components

Circuit diagrams and circuit components — practice question

Fig. 3.1 illustrates a thermistor. A thermistor is a resistor whose resistance varies with temperature changes. Fig. 3.2 illustrates a circuit that has only been partly completed.
(a)[1]

The thermistor is placed between A and B in the circuit. On Fig. 3.2, draw the correct circuit symbol for the thermistor between A and B.

(b(i))[1]

State the value of $V$ shown by the voltmeter.

(b(ii))[1]

The student then notes the voltmeter reading when the thermistor is at a constant temperature of $0^{\circ}\text{C}$. Suggest how she can lower the temperature of the thermistor from room temperature to $0^{\circ}\text{C}$ in the laboratory.

(b(iii))[2]

At $0^{\circ}\text{C}$, the voltmeter reading $V$ is $1.8\,\text{V}$. The thermistor resistance $R$, measured in ohms, is given by $R = \frac{5000}{V} - 1000$. Calculate $R$ at room temperature and at $0^{\circ}\text{C}$. Give both answers to 2 significant figures.

(b(iv))[1]

Use your results to state how the thermistor resistance varies with temperature.

Worked solution & mark scheme

This 6-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Thermistor symbol correctly drawn between A and B” …

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