Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R. Assertion A : When a rod lying freely is heated, no thermal stress is developed in it. Reason R : On heating, the length of the rod increases. In the light of the above statements, choose the corre…

Question

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R. Assertion A : When a rod lying freely is heated, no thermal stress is developed in it. Reason R : On heating, the length of the rod increases. In the light of the above statements, choose the correct answer from the options given below.

Accepted Answer

(3) Both A and R are true but R is not the correct explanation of A.. A free rod heated through Δ T simply grows to L(1+αΔ T); nothing opposes it, so there is no strain relative to its new natural length and no stress. A is true. R states that heating increases the length, which is true on its own. But the absence of stress follows from the rod being unconstrained, not from the fact that it expands: a rod clamped between rigid walls expands just as much in intent and carries a compressive stress σ=YαΔ T because of it. So R is true but is not the correct explanation of A.

Step-by-step solution

Why the other options are wrong