O-LevelPhysicsElectricity5054/41 · May/June 2023 · Q210 Marks

A student investigates a thermistor using the circuit in Fig. 2.1. [Figure 2.1]

(a)Draw a circuit diagram of the circuit.[3]
(b)The student measures the temperature of the room and records it. The recorded result is shown in Fig. 2.2. [Figure 2.2] Fig. 2.3 shows the reading Vw on the voltmeter when the switch is closed. [Figure 2.3] Record the reading Vw. Vw = ..................................................... V[1]
(c)There is a beaker containing ice and water near the thermistor. The student measures the temperature Tc of the ice and water and records it. The recorded result is shown in Fig. 2.4. [Figure 2.4] The thermistor is placed in the beaker of ice and water and after a minute, the voltmeter is read again. Fig. 2.5 shows the reading on the voltmeter when the thermistor is in the beaker of ice and water. [Figure 2.5] Record the reading Vc. Vc = ..................................................... V[1]
(d)(i)Calculate the average change in voltage for one degree temperature change ΔVᴬᴽ using the equation: ΔVᴬᴽ = (Vᴄ – Vw) / (Tᵂ – Tᴄ) State the unit of your answer ΔVᴬᴽ = .............................................. unit .....................[2]
(d)(ii)Use your answer to (d)(i) to predict the voltage Vᴾᴮ across the thermistor when the thermistor is at body temperature. Body temperature is 37°C. You may assume that the average change in voltage for one degree temperature change ΔVᴬᴽ is constant. Vᴾᴮ = ..................................................... V[1]
(d)(iii)The student is told that if the thermistor is held between a thumb and forefinger for two minutes, the reading on the voltmeter Vᴬᴮ will be the same as the predicted voltage Vᴾᴮ in (d)(ii). Two quantities are considered to be equal, within the limits of experimental accuracy, if their values are within 10% of each other. The thermistor is held between the student's thumb and forefinger for two minutes and the student reads and records the voltage Vᴬᴮ. The recorded result is shown in Fig. 2.6. [Figure 2.6] State whether the student's results indicate that Vᴾᴮ and Vᴬᴮ are equal within the limits of experimental accuracy. Support your statement with a calculation. calculation statement[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (May/June 2023). The mark or mark type is shown in brackets.

[1] three cells in the) cell / battery in series with switch, resistor and thermistor ;
[1] correct symbols of switch, resistor and thermistor ;
[1] voltmeter across thermistor ;
[1] 2(.0) (V);
[1] 2.9 (V);
[1] 0.045 (V);
[1] V/°C;
[1] from 1.0 to 1.5 (V) inclusive;
[1] statement matches results of calculation ;
[1] correct calculation to support statement using their values ;