GATE 2023 PH – Question 28

Thermodynamics and Statistical Mechanics · Laws of thermodynamics · 1 mark · Multiple select

Which of the following is(are) the CORRECT option(s) for the Joule-Thomson effect?

Show answer and explanation

Correct answer: (B) It is an isenthalpic process; (C) It can result in cooling as well as heating

Explanation

Check each statement about the **Joule-Thomson effect** (throttling of a gas through a porous plug).

**A. It is an isentropic process.** False. Throttling is irreversible, and the entropy increases.
**B. It is an isenthalpic process.** True. The enthalpy before and after is the same. ✓
**C. It can result in cooling as well as heating.** True. The Joule-Thomson coefficient $\mu_{JT}=(\partial T/\partial P)_H$ is positive below the inversion temperature (cooling) and negative above it (heating). ✓
**D. For an ideal gas it always results in cooling.** False. For an ideal gas the enthalpy depends only on temperature, so $\mu_{JT}=0$ and there is no temperature change.

Answer **B and C**.