# A student wants to find the density of a small pebble. Describe how the student would find the volume of the pebble using a measuring cylinder, and explain why taking multiple measurements of a short length on a ruler reduces the percentage uncertainty in that measurement.

> Cambridge International IGCSE Physics (0625) — 1.1 Physical quantities and measurement techniques · Describe and Explain · 4 marks

## Mark scheme (4 marks)

1. Fill the measuring cylinder with a known volume of water and record the initial reading
2. Submerge the pebble fully in the water and record the new (final) water level
3. The volume of the pebble equals the difference between the final and initial water level readings
4. For a small / short length, the uncertainty is a large fraction of the measurement; taking multiple measurements and calculating a mean reduces the percentage uncertainty / makes the result more reliable / accurate

## Key terms

- [volume](https://www.gradenine.co.uk/glossary/volume)
- [measuring cylinder](https://www.gradenine.co.uk/glossary/measuring-cylinder)
- [percentage uncertainty](https://www.gradenine.co.uk/glossary/percentage-uncertainty)

## Related

- [Revision notes for Cambridge International IGCSE Physics (0625)](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-wants-to-find-the-8a5cf245) · Published by Druglandscape Ltd.