# A student is investigating how the resistance of a wire changes with its length. She plans to measure the current through the wire and the voltage across it for five different lengths. Describe how the student should carry out this investigation to obtain valid and reliable results, and explain how she should use her measurements to find the resistance for each length.

> OCR A-Level Physics B: Advancing Physics (H557) — 1.1 Practical skills assessed · Describe · 5 marks

> The student has access to a power supply, ammeter, voltmeter, connecting leads, a metre ruler, and nichrome wire of uniform cross-sectional area.

## Mark scheme (5 marks)

1. Measure and record the length of wire using the metre ruler / set a specific length of wire between the two connection points
2. Keep variables that could affect resistance constant, such as the material / cross-sectional area / temperature of the wire
3. Record the voltmeter reading (voltage) and ammeter reading (current) for each length
4. Repeat readings for each length and calculate a mean / take repeat measurements to improve reliability
5. Divide the voltage by the current (V ÷ I) to calculate the resistance for each length

## 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)
- [voltage](https://www.gradenine.co.uk/glossary/voltage)
- [current](https://www.gradenine.co.uk/glossary/current)

## Related

- [Revision notes for OCR A-Level Physics B: Advancing Physics (H557)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" 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-is-investigating-how-the-0f3443f6) · Published by Druglandscape Ltd.