# A student is testing two different materials, Material A and Material B, by applying increasing forces to each one. Material A returns to its original shape when the force is removed, even after large forces are applied, until it suddenly snaps. Material B permanently changes shape after a certain force is exceeded and does not return to its original shape. Explain the difference between the deformation behaviour of Material A and Material B, using the correct scientific terms.

> OCR A-Level Physics A (H556) — 2.1 Physical quantities and units · Explain · 5 marks

> A student is testing two different materials, Material A and Material B, by applying increasing forces to each one. Material A returns to its original shape when the force is removed, even after large forces are applied, until it suddenly snaps. Material B permanently changes shape after a certain force is exceeded and does not return to its original shape.

## Mark scheme (5 marks)

1. Material A undergoes elastic deformation (up to the point it snaps)
2. Material A is described as brittle because it snaps rather than undergoing plastic deformation after the elastic limit
3. Material B undergoes plastic deformation beyond a certain force
4. The force beyond which Material B no longer returns to its original shape is called the elastic limit (or limit of proportionality)
5. For Material B, when the deforming force is removed beyond the elastic limit, the object does not return to its original shape (permanent distortion)

## Related

- [Revision notes for OCR A-Level Physics A (H556)](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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