# A student is investigating how a spring stretches when different forces are applied to it. The student notices that at first the extension increases steadily with force, but beyond a certain point the spring does not return to its original length when the force is removed. Explain what is happening to the spring at each stage, using the terms elastic deformation, plastic deformation, limit of proportionality, and Hooke's Law.

> OCR A-Level Physics B: Advancing Physics (H557) — 2.1 Physical quantities and units · Explain · 5 marks

> A student hangs increasing weights from a spring and records the extension each time. For the first several weights, the extension increases by the same amount for each extra weight added. After a certain point, the spring stretches much more for each extra weight and, when the weights are removed, the spring is permanently longer than it was at the start.

## Mark scheme (5 marks)

1. In the first stage, the extension is directly proportional to the force applied / the spring obeys Hooke's Law
2. In the first stage, the spring undergoes elastic deformation, so it returns to its original length when the force is removed
3. The point at which the behaviour changes is called the limit of proportionality / elastic limit, beyond which extension is no longer proportional to force
4. Beyond the limit of proportionality / elastic limit, the spring undergoes plastic deformation
5. After plastic deformation, the spring does not return to its original shape / length when the deforming force is removed

## Key terms

- [elastic deformation](https://www.gradenine.co.uk/glossary/elastic-deformation)
- [plastic deformation](https://www.gradenine.co.uk/glossary/plastic-deformation)
- [limit of proportionality](https://www.gradenine.co.uk/glossary/limit-of-proportionality)
- [Hooke's Law](https://www.gradenine.co.uk/glossary/hooke-s-law)
- [extension](https://www.gradenine.co.uk/glossary/extension)

## Related

- [Revision notes for OCR A-Level Physics B: Advancing Physics (H557)](https://www.gradenine.co.uk/learn)
- [How to answer "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-is-investigating-how-a-b2ba240a) · Published by Druglandscape Ltd.