CAIE A-Level Physics 10.3.4 Thermistor and LDR Potential Dividers

Practise predicting and calculating thermistor or LDR potential-divider outputs as temperature or light changes, using resistance position and divider relationships.

Exam points

explain how a thermistor or LDR in a potential divider makes output p.d. depend on temperature or light intensity
predict the direction of output-p.d. change from the sensor’s resistance change and its position in the divider
apply the divider relationship to a temperature- or light-dependent circuit

[Maximum number: 1]

The diagram shows a circuit with a battery of electromotive force (e.m.f.) 60 V and negligible internal resistance, a $20 \mathrm{k} \Omega$ resistor, a thermistor and a voltmeter. The resistance of the thermistor is $20 \mathrm{k} \Omega$ .

Figure for Question 10.3.4—The use of thermistors and light-dependent resistors in potential dividers question 1 — CAIE A-Level Physics AS

The temperature of the thermistor decreases, and this causes its resistance to change by 50%.
After this change, what is the reading on the voltmeter?
A 20 V
B 24 V
C 36 V
D 40 V

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10.3.4—The use of thermistors and light-dependent resistors in potential dividers question 1