# A student measures the mass of a metal block five times using a digital balance. His results are: 84.2 g, 84.3 g, 84.2 g, 84.3 g, 84.2 g. The manufacturer's specification states the true mass of the block is 86.5 g. Describe the accuracy and precision of these measurements and explain what type of error is most likely responsible for the difference between the mean of the student's results and the true value.

> AQA A-Level Physics (7408) — 3.1.2 Limitations of Physical Measurements · Describe · 5 marks

## Mark scheme (5 marks)

1. The measurements are precise because the values are close together / there is a small range / low spread in the results
2. The measurements are not accurate because the mean is not close to the true value (86.5 g)
3. Correct calculation or identification of the mean as approximately 84.2 g or 84.24 g
4. The type of error responsible is a systematic error
5. Explanation of why it is systematic — the balance gives readings that are consistently too low / there is a zero error / the balance is not calibrated correctly, so repeating measurements does not reduce the error

## Key terms

- [accuracy](https://www.gradenine.co.uk/glossary/accuracy)
- [precision](https://www.gradenine.co.uk/glossary/precision)
- [mean](https://www.gradenine.co.uk/glossary/mean)
- [true value](https://www.gradenine.co.uk/glossary/true-value)

## Related

- [Revision notes for AQA A-Level Physics (7408)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-measures-the-mass-of-6bb275f1) · Published by Druglandscape Ltd.