Heat the water, time the rise. Keep the temperature rise constant.
Electrical heating of a liquid is a recurring Question 1 family in Paper 5. Here an immersion heater warms a fixed mass of water, and you measure the time t for a fixed temperature rise as the p.d. V across the heater changes. Watch the set-up built step by step, with the variables and the graph beside it, then build it yourself and check it against the mark points.
Past-paper referenceOriginal experiment, wording and figures, written in the style of Cambridge AS & A Level Physics 9702 Paper 5, Question 1. It is not copied from a past paper. The “what the examiners said” notes are our paraphrase of the Principal Examiner Reports for Teachers.
Practise next: 9702/53 October/November 2015, Question 1 (energy supplied by a heater in water containing metal blocks) · official past papers
Practise next: 9702/52 October/November 2024, Question 1 (temperature rise of oil heated by a resistance-wire coil) · official past papers
Practise next: 9702/51 May/June 2024, Question 1 (cooling of a heated, insulated metal cylinder) · official past papers
Examiner reports used: 9702 November 2015, June 2024 and November 2024.
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What a full-mark diagram shows
The heater circuit
A power supply connected to the heater, with a voltmeter in parallel with the heater only. No meter across a variable resistor as well.
Thermometer in the liquid
A labelled thermometer with its bulb in the water, and the heater fully submerged. No Bunsen burner or water bath.
Measuring the variables
A stopwatch started at switch-on; Δθ = final − initial temperature; m from a balance by subtraction.
Analysis
1/t against V2, valid if a straight line (not through the origin); H = 1/gradient, J = −y-intercept/gradient.
Habits the examiner reports keep asking for
Keep the temperature rise constant, not “the temperature”, and never just “control” it.
A temperature change is two readings: the initial and the final temperature, subtracted.
Describe the mass by difference: weigh the empty beaker, then the beaker and water. Say balance, not “a scale”.
Stir, insulate, and start from the same temperature: these are credited details for this experiment.
Safety in this experiment is about hot water and spills. Gloves for the hot heater and beaker, a tray under the beaker.