# A student investigates how the resistance of a wire changes with the length of the wire. She plans to measure the current through the wire and the voltage across it for six different lengths. Explain how the student should carry out a valid and reliable investigation, including how she would use her results to find the resistance at each length.

> Edexcel A-Level Physics (9PH0) — 1.1 Practical and investigative skills · Explain · 5 marks

> A student investigates how the resistance of a wire changes with the length of the wire. She uses a circuit with a power supply, an ammeter, a voltmeter, and a length of resistance wire.

## Mark scheme (5 marks)

1. Keep all other variables constant / control variables (e.g. same wire material, same cross-sectional area, same temperature / allow wire to cool between readings)
2. Repeat each measurement (at least twice / three times) and calculate a mean value for current or voltage
3. Use the voltmeter connected in parallel across the wire and the ammeter connected in series to measure voltage and current
4. Use the equation V = IR (rearranged as R = V/I) to calculate resistance at each length
5. Identify and discard anomalous results before calculating the mean / check for anomalies in the data

## Key terms

- [resistance](https://www.gradenine.co.uk/glossary/resistance)
- [valid](https://www.gradenine.co.uk/glossary/valid)
- [reliable](https://www.gradenine.co.uk/glossary/reliable)

## Related

- [Revision notes for Edexcel A-Level Physics (9PH0)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-investigates-how-the-resistance-299ddc94) · Published by Druglandscape Ltd.