# A student measures the voltage across a battery using a voltmeter. He takes five readings: 9.1 V, 9.0 V, 8.6 V, 9.1 V, 9.0 V. Explain how the student should process these results to obtain the most reliable value for the voltage, and explain why one of the readings should be treated differently from the others.

> AQA A-Level Physics (7408) — 3.1.2 Limitations of Physical Measurements · Explain · 5 marks

## Mark scheme (5 marks)

1. Identifies 8.6 V as an anomalous result / outlier
2. States that the anomalous result should be excluded / not included in the mean calculation
3. States that the mean (average) of the remaining values should be calculated
4. Explains that taking repeated measurements reduces the effect of random error
5. Explains that the anomalous result may have been caused by a random error (e.g. a sudden fluctuation or misreading) making it unrepresentative

## Related

- [Revision notes for AQA A-Level Physics (7408)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-measures-the-voltage-across-0e93cf0e) · Published by Druglandscape Ltd.