# Explain why alpha particles are described as highly ionising but weakly penetrating.

> Cambridge International IGCSE Physics (0625) — 5.2 Radioactivity · Explain · 4 marks

## Mark scheme (4 marks)

1. Alpha particles have a large (positive) charge / carry charge of +2
2. The large charge means alpha particles interact strongly with / remove electrons from surrounding atoms, forming ions
3. Because alpha particles ionise so frequently / lose energy rapidly to surrounding matter
4. So they are stopped after a short distance / stopped by a few centimetres of air or a sheet of paper

## Key terms

- [alpha particle](https://www.gradenine.co.uk/glossary/alpha-particle)
- [ionising](https://www.gradenine.co.uk/glossary/ionising)
- [penetrating](https://www.gradenine.co.uk/glossary/penetrating)
- [ion](https://www.gradenine.co.uk/glossary/ion)

## Related

- [Revision notes for Cambridge International IGCSE Physics (0625)](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/explain-why-alpha-particles-are-described-69f1fc3b) · Published by Druglandscape Ltd.