Question

Hooke’s law is valid up to:

• A. Breaking point
• B. Yield point
• C. Elastic limit
• D. Ultimate stress

Hint:

Always remember: {Hooke’s law works only in the elastic region} of the stress–strain curve.

Answer 1

The Correct Option is C

Step 1: What Hooke’s law tells us. 
Hooke’s law describes how materials behave when they are stretched or compressed. It states that, for small deformations, the stress produced in a material is directly proportional to the strain:

\[ \text{Stress} = E \times \text{Strain} \]

Here, \(E\) is the modulus of elasticity, which measures the stiffness of the material.

Step 2: Meaning of the elastic limit.
The elastic limit is the highest stress a material can experience and still return completely to its original shape once the load is removed. Below this limit, deformation is fully reversible.

Step 3: Validity range of Hooke’s law.
The straight-line (proportional) relationship between stress and strain exists only in the elastic region. As soon as the elastic limit is crossed, the stress–strain curve becomes non-linear, and Hooke’s law no longer applies.

Step 4: Evaluating the options.
(A) Breaking point – occurs after complete failure; Hooke’s law is not valid here.
(B) Yield point – plastic deformation starts; proportionality is lost.
(C) Elastic limit – proportional stress–strain behavior holds up to this point.
(D) Ultimate stress – maximum stress before fracture, well beyond elastic behavior.

Step 5: Final conclusion.
Hooke’s law remains applicable only as long as the material stays within its elastic limit.

\[ \boxed{\text{Elastic limit}} \]