# A sealed syringe contains a fixed amount of air. The plunger is pushed inward, reducing the volume of the air while the temperature stays the same. Explain, using kinetic theory, why the pressure of the air increases when its volume is decreased.

> Eduqas A-Level Physics — 3.3 Kinetic theory · Explain · 5 marks

> A sealed syringe has its plunger pushed inward so the volume of the trapped air is made smaller. The temperature of the air does not change.

## Mark scheme (5 marks)

1. Air is made up of particles (molecules/atoms) that are constantly moving
2. Pressure is caused by particles colliding with the walls of the container
3. When volume decreases, the particles are closer together / confined to a smaller space
4. Particles collide with the walls more frequently / more often
5. More frequent collisions means a greater force on the walls per unit area, so pressure increases

## Key terms

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

## Related

- [Revision notes for Eduqas A-Level 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-fd58d798) · Published by Druglandscape Ltd.