A Level Physics Practice Exam

What happens when the limit of proportionality of a material is exceeded?

1. The material breaks immediately

2. The material returns to original length

3. The relationship between force and extension is no longer linear

4. The material becomes non-elastic

The correct answer is: The relationship between force and extension is no longer linear

When the limit of proportionality of a material is exceeded, the relationship between force and extension is no longer linear. In the elastic region of a material's behavior, Hooke's Law applies, which states that the force exerted on the material is directly proportional to the extension experienced by that material. This relationship holds true up to a certain point known as the limit of proportionality. Once this limit is surpassed, the material enters a region where it may still stretch, but the force needed to produce further extension increases at a different rate, breaking the linear relationship. Beyond this limit, the material may begin to exhibit plastic deformation, meaning it will not return to its original shape when the force is removed, and behavior becomes increasingly complex and nonlinear. This is a critical concept in understanding material properties and mechanical behavior under stress.