# A student investigates how the density of different liquids varies. She measures the mass and volume of five different liquid samples and records her results. Describe how the student should ensure her results are valid and reliable, and explain how she should identify and deal with any anomalous results.

> Edexcel A-Level Physics (9PH0) — 1.1 Practical and investigative skills · Describe · 5 marks

> A student is planning an investigation to measure the density of five different liquids using a measuring cylinder and a balance. She intends to use her results to draw a conclusion about how density varies between the liquids.

## Mark scheme (5 marks)

1. She should control all variables that could affect the measurements, such as temperature or the volume of liquid used each time.
2. She should repeat each measurement (at least three times) and calculate a mean to improve reliability.
3. She should use appropriate measuring equipment with a suitable resolution, e.g. a balance measuring to at least 0.1 g and a measuring cylinder with small graduations.
4. An anomalous result is one that does not fit the pattern of the other results / lies well outside the range of the other values.
5. Anomalous results should not be included when calculating the mean; she should repeat the measurement to check whether it is a genuine outlier or a one-off error.

## Key terms

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

## Related

- [Revision notes for Edexcel A-Level Physics (9PH0)](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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-investigates-how-the-density-e9b27067) · Published by Druglandscape Ltd.