9702_s22_qp_12 Question 20

A wire is being stretched by a tensile force.

Which statement about the elastic limit must be correct?

A The deformation is plastic after the elastic limit has been reached.

B The deformation is plastic until the elastic limit is reached.

C The extension is proportional to the tensile force after the elastic limit has been reached.

D The extension is proportional to the tensile force until the elastic limit is reached.

ANSWER: A

The Physics Behind

• If you apply a small force to a wire [or spring] and then release it, it will return to its original length (this is elastic deformation.). However, if you apply a large force, the wire [spring] may not return to its original length; the spring has become permanently deformed (this is plastic deformation.). 
• The force beyond which the wire [spring] becomes permanently deformed is known as the elastic limit.
• This is also to say that beyond the elastic limit, the wire will have permanent deformation which is called plastic.