# A student measures the activity of a radioactive sample using a Geiger-Muller tube and records a value of 340 becquerels. Explain what is meant by the term 'activity', state what unit it is measured in, and describe how the activity of the sample will change over time.

> Pearson Edexcel International GCSE Physics (4PH1) — 7.1 Units · Explain · 4 marks

## Mark scheme (4 marks)

1. Activity is the number of (radioactive/nuclear) decays per unit time / the rate at which unstable nuclei decay
2. Activity is measured in becquerels (Bq)
3. The activity decreases / reduces over time
4. This is because unstable nuclei are used up / the number of unstable nuclei remaining decreases as decay occurs, so fewer decays happen each second

## Key terms

- [activity](https://www.gradenine.co.uk/glossary/activity)
- [becquerel](https://www.gradenine.co.uk/glossary/becquerel)

## Related

- [Revision notes for Pearson Edexcel International GCSE Physics (4PH1)](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-measures-the-activity-of-363b97e1) · Published by Druglandscape Ltd.