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JEE Main202125 Feb 2021Morning ShiftPhysicsThermal Properties of MatterActual

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:

Options

  1. ABoth A and R are true and R is the correct explanation of A
  2. BA is false but R is true
  3. CBoth A and R are true but R is NOT the correct explanation of A
  4. DA is true but R is false

Correct answer

C. Both A and R are true but R is NOT the correct explanation of A

Step-by-step solution

Thermal stress is mechanical stress created by any change in temperature of a material. When the body is under some constraints, thermal stress is generated. But if it is lying freely, no thermal stress is developed. The increase in length of a body with temperature is given by ∆ L = L α ∆ T So, with the increase in temperature, the length of the rod increases. A and R are true but R is not the correct explanation of A .

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