# Practical investigations and data analysis

> Planning, measuring, graphing and evaluating a physics investigation so that a conclusion follows from evidence rather than from a neat-looking line.

Canonical: https://revise-gray.vercel.app/library?topic=wjec-alevel-physics.practical-investigations
Last updated: 2026-08-01

Flagship subject: topics and specification statements are authored to the WJEC specification. No question in it has been through human review yet.

- Subject: [WJEC · A Level · Physics](https://revise-gray.vercel.app/library?subject=wjec-alevel-physics)
- Specification reference: Unit 5
- Difficulty: 4/5
- Assessment objectives: AO1, AO2, AO3
- Status: authored · checked · 2026-08-01

## Specification coverage

| Reference | Statement | AOs |
| --- | --- | --- |
| Unit 5(a) | plan a safe investigation with variables controls and repeat measurements | AO2, AO3 |
| Unit 5(b) | distinguish random uncertainty systematic error accuracy and precision | AO1, AO2 |
| Unit 5(c) | linearise data and determine a gradient intercept and their uncertainties | AO2, AO3 |
| Unit 5(d) | draw evidence-based conclusions and evaluate a method with targeted improvements | AO2, AO3 |

## Summary

Planning, measuring, graphing and evaluating a physics investigation so that a conclusion follows from evidence rather than from a neat-looking line.

## What earns marks

- A valid investigation changes one independent variable, measures a defined dependent variable and controls quantities that could otherwise explain the result.
- Random uncertainty is reduced by repeats and averaging; systematic error shifts every result and needs calibration, a better method or an explicit limitation.
- Linearising a relationship makes the gradient and intercept meaningful; units, significant figures and uncertainty must be carried through the calculation.
- A conclusion should state the relationship, quote evidence and explain the range of validity; evaluation proposes a specific improvement and predicts its effect.

## Where marks are lost

- Saying repeats remove systematic error.
- Drawing a best-fit line through the origin without evidence that the intercept is zero.
- Calling a result precise because the graph is smooth while ignoring a large scale uncertainty.

## Related

- [WJEC · A Level · Physics](https://revise-gray.vercel.app/library?subject=wjec-alevel-physics)
- [Practical investigations and data analysis lesson](https://revise-gray.vercel.app/lesson?subject=wjec-alevel-physics&topic=wjec-alevel-physics.practical-investigations)