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 :
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 :
- (A)Both and are true and is the correct explanation of
- (B) is false but is true
- (C) is true but is false
- (D)Both and R are true but is NOT the correct explanation of A✓ Correct
Answer: (D)
Solution
Assertion A is true: when a rod is free to expand (not constrained), no thermal stress develops because the rod can expand freely without any opposing force.
Reason R is also true: on heating, thermal expansion causes the length of the rod to increase.
However, R is NOT the correct explanation of A. The absence of thermal stress is because the rod is free to expand (unconstrained), not simply because its length increases. If the expansion were hindered, stress would develop even though the length tries to increase. Both statements are true but R does not explain A.
Reason R is also true: on heating, thermal expansion causes the length of the rod to increase.
However, R is NOT the correct explanation of A. The absence of thermal stress is because the rod is free to expand (unconstrained), not simply because its length increases. If the expansion were hindered, stress would develop even though the length tries to increase. Both statements are true but R does not explain A.
JEE Main · 2021 · 25 Feb 2021 · Shift 1 · Single correct option