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Date May 2015 Marks available 1 Reference code 15M.2.HL.TZ1.3
Level Higher level Paper Paper 2 Time zone Time zone 1
Command term Define Question number 3 Adapted from N/A

Question

This question is about a thermistor circuit.

The circuit shows a negative temperature coefficient (NTC) thermistor X and a 100 kΩ fixed resistor R connected across a battery.

The battery has an electromotive force (emf) of 12.0 V and negligible internal resistance.

Define electromotive force (emf).

[1]
a.

The graph below shows the variation with temperature T of the resistance RX of the thermistor.

(i) Determine the temperature of X when the potential difference across R is 4.5 V.

(ii) State the range of temperatures for which the change in the resistance of the thermistor is most sensitive to changes in temperature.

(iii) State and explain the effect of a decrease in temperature on the ratio voltageacrossXvoltageacrossR.

[7]
b.

Markscheme

the work done per unit charge in moving a quantity of charge completely around a circuit / the power delivered per unit current / work done per unit charge made available by a source;

a.
(i) VX = 7.5 (V);
I(=4.5100×103)=4.5×105A or VXVR=RXRR;
RX(=7.54.5×105)=1.67×105Ω or RX(=7.54.5×100×103)=1.67×105Ω;
T=37 or 38 °C
(ii) 50 to (up to) 30 °C / at low temperatures;
(iii) as the temperature decreases Rx increases; same current through R and X so the ratio increases or VX increases and VR decreases so the ratio increases;
b.

Examiners report

[N/A]
a.
[N/A]
b.

Syllabus sections

Core » Topic 5: Electricity and magnetism » 5.3 – Electric cells
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