Circuits with a crocodile clip on a resistance wire are the most common Question 1 in 9702 Paper 3. Use your hand on the bench: slide clip G along the wire, press the switch down to read the ammeter, then turn a micrometer onto the wire. Tabulate, plot 1/I against x and work through to the resistivity. Every attempt uses a different wire and cell. Allow about 45 minutes.
Past-paper referenceOriginal experiment, wording and numbers, written in the style of Cambridge AS & A Level Physics 9702 Paper 3, Question 1. It is not copied from a past paper.
Practise next: 9702/33 February/March 2025, Question 1 (crocodile clips on a resistance wire, graph of 1/I against x) · official past papers
Practise next: 9702/33 October/November 2024, Question 1 (the resistivity of a metal, with a micrometer for the diameter) · official past papers
This type of experiment has come up 13 times in the past papers we checked. Show the list
Checked: Cambridge 9702 Paper 3, 2017 to 2019 and 2023 to 2025. Only the papers in our collection are listed, so the real number may be higher. Question papers are available from Cambridge.
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How this question is marked
Measurements (a)
x to the nearest millimetre and I as the ammeter shows it.
Table (b)
Six sets over a wide range of x, headings with units, raw readings recorded consistently, and 1/I to the same significant figures as I (or one more).
Graph (c)
Axes and scales, plotting, the line of best fit, a large gradient triangle and the y-intercept, marked as in the graph trainer.
Analysis (d), (e), (f)
a and b from your own gradient and intercept with units, the diameter from the micrometer, P = aE and the resistivity with its unit, and why the switch is opened between readings.
Habits that save marks
Open the switch between readings. A current heats the wire, its resistance rises and the reading drifts.
Read x at the jaw of the clip, where it touches the wire, to the nearest millimetre.
Close the micrometer with the ratchet, so you do not squash the wire, then add sleeve and thimble readings.
Convert d to metres before using ρ = πd²P/4.
The marking follows the conventions in published Cambridge mark schemes. The experiments, readings and wording on this page are our own.