# A sealed syringe contains a fixed amount of gas. The plunger is pushed in slowly so that the volume of the gas decreases, but the temperature of the gas stays the same. Explain why the pressure of the gas increases.

> Eduqas GCSE Physics — 2.2 The kinetic theory and gas pressure · Explain · 4 marks

## Mark scheme (4 marks)

1. The gas particles collide with the walls of the syringe (container)
2. Pressure is caused by these collisions / pressure is the perpendicular force per unit area from particle collisions
3. Decreasing the volume means the same number of particles is contained in a smaller space
4. So particles collide with the walls more frequently, increasing the pressure

## Key terms

- [pressure](https://www.gradenine.co.uk/glossary/pressure)
- [volume](https://www.gradenine.co.uk/glossary/volume)
- [temperature](https://www.gradenine.co.uk/glossary/temperature)

## Related

- [Revision notes for Eduqas GCSE Physics](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-sealed-syringe-contains-a-fixed-a25f1b78) · Published by Druglandscape Ltd.