# A student is investigating how the length of a wire affects its resistance. Describe how the student should make their investigation a fair test and explain why repeating measurements and calculating a mean improves the reliability of their results.

> OCR GCSE Physics A: Gateway Science (J249) — P9 Practical skills · Describe · 4 marks

> A student sets up a circuit to measure the resistance of different lengths of resistance wire. They plan to change the length of the wire and measure the resistance each time.

## Mark scheme (4 marks)

1. Keep all other variables constant / the same (e.g. same type of wire, same thickness/diameter of wire, same temperature)
2. Only change the independent variable (length of wire) and measure the dependent variable (resistance)
3. Repeating measurements reduces the effect of random errors / anomalous results
4. Calculating a mean gives a more reliable / accurate value for the resistance

## Key terms

- [fair test](https://www.gradenine.co.uk/glossary/fair-test)
- [mean](https://www.gradenine.co.uk/glossary/mean)
- [reliability](https://www.gradenine.co.uk/glossary/reliability)

## Related

- [Revision notes for OCR GCSE Physics A: Gateway Science (J249)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-is-investigating-how-the-896bfb7a) · Published by Druglandscape Ltd.