# A student investigates how the time taken for a piece of toast to cool down depends on its initial temperature. She heats the toast to different starting temperatures and records the time taken for it to cool to room temperature. Explain how the student could ensure her investigation produces valid and reliable results.

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

> The student uses a thermometer to measure temperature and a stopwatch to measure time. She is concerned that her results may not be trustworthy.

## Mark scheme (5 marks)

1. Identify and control a relevant control variable
2. Explain why controlling that variable makes the results valid
3. Repeat measurements / take repeat readings at each starting temperature
4. Use the repeated values to calculate a mean / identify and exclude anomalous results
5. Use an appropriate range of starting temperatures / take a sufficient number of different values of the independent variable

## Key terms

- [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-time-0585b2ee) · Published by Druglandscape Ltd.