Adiabatic Expansion and Gas Temperature – Rankers Physics

Kinetic Theory of Gases: Practice Problem & Solution

Assertion (A): A gas is kept in an insulated cylinder with a movable piston, in compressed state. As the piston is suddenly released, temperature of the gas decreases. Reason (R): According to the kinetic theory of gas, a molecule colliding with the piston must rebound with less speed than it had before the collision. Hence average speed of the molecules is reduced.  
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 Explained:

To solve this problem, we apply the core principles of Kinetic Theory of Gases. Understanding the underlying formula is key to arriving at the correct answer below:

In an adiabatic expansion, the gas does work on the receding piston. Molecules lose kinetic energy upon collision, reducing their average speed and thus the gas temperature. Reason (R) correctly explains Assertion (A).

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