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JEE Main 2025 Jan 24 Shift 2, Physics Q6: Thermodynamic Processes

JEE Main2025Jan 24, Shift 2Physics
Q.

Given below are two statements. One is labelled as Assertion (A) and the other is labelled as Reason (R).

Assertion (A) : In an insulated container, a gas is adiabatically shrunk to half of its initial volume. The temperature of the gas decreases.

Reason (R) : Free expansion of an ideal gas is an irreversible and an adiabatic process.

In the light of the above statement, choose the correct answer from the options given below :

  1. A

    Both (A) and (R) are true and (R) is the correct explanation of (A)

  2. B

    (A) is true but (R) is false

  3. C

    (A) is false but (R) is true

  4. D

    Both (A) and (R) are true but (R) is NOT the correct explanation of (A)

Solution

Assertion: For a reversible adiabatic process on an ideal gas, . Compressing to half the volume ():

Since , — the temperature rises on adiabatic compression. The Assertion claims it falls, so (A) is false.

Reason: Free expansion (gas into vacuum) is uncontrolled and rapid, so no heat is exchanged with the surroundings (adiabatic) and it cannot be reversed without external intervention (irreversible). So (R) is true.

Correct option: (3)

Concept behind this question

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