Explain what is meant by a material being described as brittle and describe how a brittle material behaves differently from a ductile material when a tensile force is applied beyond the elastic limit.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
A brittle material does not deform plastically before breaking – it snaps or fractures suddenly without significant permanent deformation.
A ductile material can be stretched beyond the elastic limit and undergoes plastic deformation, changing shape permanently without breaking.
Beyond the elastic limit the ductile material does not return to its original shape – the deformation is permanent.
The brittle material breaks or fractures at or close to the elastic limit, showing no plastic region.
Thus, a brittle material fractures suddenly, whereas a ductile material continues to deform and extend without immediately breaking.
A ductile material can be stretched beyond the elastic limit and undergoes plastic deformation, changing shape permanently without breaking.
Beyond the elastic limit the ductile material does not return to its original shape – the deformation is permanent.
The brittle material breaks or fractures at or close to the elastic limit, showing no plastic region.
Thus, a brittle material fractures suddenly, whereas a ductile material continues to deform and extend without immediately breaking.
Examiner tips
- Use the terms "brittle" and "ductile" explicitly. Show the contrast in behaviour beyond the elastic limit. Include the idea of plastic deformation for ductile and lack of it for brittle. Keep the answer concise – 5 marks only.
Common mistakes
- Confusing elastic and plastic deformation. Saying a brittle material deforms plastically. Omitting the point that brittle materials break near the elastic limit.
Mark scheme (5 marks)
- A brittle material does not deform plastically (before breaking) / snaps or fractures suddenly without significant permanent deformation
- A ductile material can be stretched beyond the elastic limit and undergoes plastic deformation / changes shape permanently without breaking
- Beyond the elastic limit the ductile material does not return to its original shape / the deformation is permanent
- The brittle material breaks/fractures at or close to the elastic limit / without showing a plastic region
- Correct comparison: brittle material fractures suddenly whereas the ductile material continues to deform/extend without immediately breaking
Key terms in this question
brittle · ductile · elastic limit · tensile force
Related
- All AQA A-Level Physics (7408) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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