# A student is investigating the density of different materials. She measures the mass of a rectangular block of aluminium using a balance. She then measures the length, width and height of the block using a ruler to find its volume. She repeats each measurement three times and records her results. Describe how the student should use her repeated measurements to obtain reliable values for mass and volume, and explain why repeating measurements improves the quality of her results.

> OCR A-Level Physics B: Advancing Physics (H557) — 1.1 Practical skills assessed · Describe · 5 marks

> Density is defined as the mass per unit volume of an object. A student wants to determine the density of an aluminium block as accurately as possible.

## Mark scheme (5 marks)

1. The student should calculate the mean (average) of the three repeated measurements for each dimension (or mass).
2. Any anomalous (outlier) results should be identified and excluded before calculating the mean.
3. Use the mean values for length, width, and height to calculate the volume of the block (length × width × height).
4. Repeating measurements reduces the effect of random errors.
5. Taking the mean of repeated measurements gives a more accurate / reliable value (closer to the true value).

## Key terms

- [density](https://www.gradenine.co.uk/glossary/density)
- [reliable](https://www.gradenine.co.uk/glossary/reliable)

## Related

- [Revision notes for OCR A-Level Physics B: Advancing Physics (H557)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" 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-is-investigating-the-density-4ed87232) · Published by Druglandscape Ltd.