# A student investigates how the pressure of a fixed mass of gas changes when its volume is changed at constant temperature. They use a sealed syringe connected to a pressure sensor. The student pushes the plunger in to reduce the volume of the gas, recording the pressure at each volume. Describe what the student should do to make this a fair test and explain the relationship between pressure and volume that the results should show.

> OCR A-Level Physics A (H556) — 1.1 Practical skills assessed · Describe and Explain · 5 marks

> A student compresses a fixed mass of air inside a sealed syringe and measures the pressure at different volumes, keeping the temperature constant throughout.

## Mark scheme (5 marks)

1. The temperature must be kept constant throughout the investigation
2. The mass (or amount) of gas must remain fixed / the syringe must remain sealed so no gas escapes
3. Pressure and volume are inversely proportional
4. As the plunger is pushed in, the volume decreases so gas particles collide with the walls of the syringe more frequently
5. More frequent collisions with the walls result in a greater force per unit area, so pressure increases

## Key terms

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

## Related

- [Revision notes for OCR A-Level Physics A (H556)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe and 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-pressure-fd6db290) · Published by Druglandscape Ltd.