# A student investigates how the extension of a spring varies with the force applied to it. She repeats each measurement three times and calculates a mean extension for each force value. Explain why repeating measurements and calculating a mean improves the quality of the data collected, and describe one additional step the student should take to check the validity of her results.

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

> A student hangs different weights from a spring and measures the extension each time. She repeats each measurement three times.

## Mark scheme (5 marks)

1. Repeating measurements reduces the effect of random errors / anomalous results
2. Calculating the mean gives a more reliable / precise value for the extension
3. The student should identify and exclude any anomalous results before calculating the mean
4. The student should check her results show a pattern consistent with Hooke's law (extension proportional to force) to assess validity
5. The student should take a reading with no weight applied (zero force) to establish a reference / zero extension point, OR ensure the independent variable (force) is changed in equal steps to allow a fair comparison

## Key terms

- [mean](https://www.gradenine.co.uk/glossary/mean)
- [validity](https://www.gradenine.co.uk/glossary/validity)
- [extension](https://www.gradenine.co.uk/glossary/extension)

## 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-extension-d7825197) · Published by Druglandscape Ltd.