CAIE A-Level Physics 9.3.8 NTC Thermistor

Practise explaining how an NTC thermistor’s resistance falls as temperature rises and applying that relationship to circuits or temperature sensors.

Exam points

explain that a thermistor with negative temperature coefficient has lower resistance as temperature increases
interpret or apply the thermistor relationship in a circuit or temperature-sensing context

[Maximum number: 1]

A battery of electromotive force (e.m.f.) 12 V and negligible internal resistance is connected to a fixed resistor of resistance $40 \Omega$ and a thermistor of resistance $R_{\mathrm{T}}$ , as shown.

Figure for Question 9.3.8—The resistance of a thermistor decreases as the temperature increases (it question 1 — CAIE A-Level Physics AS

Initially, the temperature of the thermistor is $15^{\circ} \mathrm{C}$ and the current in the circuit is 0.10 A .
The temperature of the thermistor then changes, which causes the current to increase to 0.12 A .
How does the temperature of the thermistor change and what is $R_{\mathrm{T}}$ at the new temperature?

temperature

of thermistor

$R_{\mathrm{T}}$ at new

temperature $/ \Omega$

increases

decreases

increases

100

decreases

100

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9.3.8—The resistance of a thermistor decreases as the temperature increases (it question 1