A Level Physics Practice Exam

Plastic deformation refers to the process by which a material undergoes a permanent change in shape or size when subjected to stress beyond its yield strength. This means that the material does not return to its original dimensions after the removal of the applied load. In this context, the correct answer is that plastic deformation implies a permanent extension.

When a material is plastically deformed, the atomic structure of the material experiences a rearrangement that is not reversible, leading to a lasting alteration in its form. This is distinctly different from elastic deformation, where the material will return to its original shape once the stress is removed.

The concept of temporary extension applies to elastic deformation, where the material recovers fully after the load is taken off. Similarly, the idea of permanently removed stress misrepresents the situation, since the stress does not vanish—it causes the material to change. The final option regarding elastic recovery of material also does not pertain to plastic deformation, as that specifically refers to the reversible process of elastic deformation.