NEET Physics Question - Thermal Physics

Assertion (A): In a free adiabatic expansion of an ideal gas, the final state is the same as the initial state.

Reason (R): As temperature of a gas increases work done by it is positive.

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

Both (A) & (R) are true but the (R) is not the correct explanation of the (A)

(A) is true but (R) is false

Both (A) and (R) are false

Solution:

For free adiabatic expansion, \( Q = 0 \) and \( W = 0 \). According to the first law of thermodynamics, \( \Delta U = Q - W = 0 \). For an ideal gas, \( \Delta U = nC_v\Delta T \), so \( \Delta T = 0 \), meaning the final temperature is the same as the initial temperature. However, the final state (P,V,T) is not entirely the same as the initial state, only T is.

Thus, Assertion (A) is false. If temperature increases, work done by the gas can be positive, but it is not a direct consequence, and expansion (positive work) typically cools the gas. So, Reason (R) is also false. Therefore, both (A) and (R) are false.

Rankers Physics

Free Adiabatic Expansion

Solution:

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