O-LevelPhysicsThermal Physics5054/41 · Oct/Nov 2025 · Q110 Marks

A student measures the efficiency of a small electric heater.

(a)The student is provided with the circuit shown in Fig. 1.1. The coil of wire is the small electric heater. Draw on the circuit in Fig. 1.1 to show a voltmeter connected to measure the potential difference across the heater.[1]
(b)(i)The student is also provided with: • a thermometer • a stirrer • a measuring cylinder containing water at room temperature • a stopwatch. Fig. 1.2 shows the volume of water W in the measuring cylinder. Record the volume of water W. W = cm³[1]
(b)(ii)The student: • pours the water from the measuring cylinder into the beaker containing the heater • makes sure that the heater is covered by water • closes the switch • records the readings on the voltmeter and ammeter • opens the switch. Fig. 1.3 shows the reading on the voltmeter and on the ammeter when the switch is closed. Record the potential difference V and the current I. V = V I = A[1]
(c)(i)The thermometer is placed in the water in the beaker. Fig. 1.4 shows the initial temperature θ₀ of the water. Record the initial temperature of the water in the beaker. θ₀ = °C[1]
(c)(ii)The student: • closes the switch and immediately starts the stopwatch • leaves the heater switched on for 5 minutes • stirs the water while the heater is switched on • opens the switch • continues to stir the water for a further minute • records the final temperature θf. The final temperature θf is 24.5°C. Calculate the temperature change Δθ. Use the equation shown. Δθ = θf – θ₀ Δθ = °C[1]
(c)(iii)Explain why the student continues to stir the water for a further minute after the heater is switched off.[1]
(d)(i)The energy QH supplied by the heater is given by QH = I × V × t where t = 300 s. Calculate QH. Show your working. QH = J[1]
(d)(ii)The energy QW gained by the water is given by the equation shown. QW = W × 4.2 × Δθ Calculate QW using your value of W from (b)(i) and your value of Δθ from (c)(ii). Show your working. QW = J[1]
(d)(iii)The efficiency of the heater is given by the equation shown. efficiency = QW / QH Calculate the efficiency of the heater. Show your working. efficiency = [1]
(e)Suggest one change that can be made to the apparatus used in this investigation that will increase the efficiency of the heater.[1]

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 (Oct/Nov 2025). The mark or mark type is shown in brackets.

[1] voltmeter drawn with correct symbol in parallel across heater
[1] 52(.0) (cm³)
[1] 3.4(0) (V) and 1.45 (A) both correct
[1] 21(.0) °C
[1] 3.5 °C
[1] (to ensure the water is at) a uniform temperature / (to ensure that) all the heat from the coil is absorbed by the water
[1] 1500 / 1480 / 1479 (J)
[1] 760 / 764 / 764.4 (J)
[1] correct calculation of efficiency from candidate's values of QW and QH (expect 0.51 to 0.52)
[1] insulate / add a lid to the beaker