# Thermodynamics Questions and Answers – Joule-Kelvin Effect

«
»

This set of Thermodynamics Multiple Choice Questions & Answers (MCQs) focuses on “Joule-Kelvin Effect”.

1. When a gas undergoes continuous throttling process by a valve and its pressure and temperature are plotted, then we get a
a) isotherm
b) isenthalpe
d) isobar

Explanation: All the points plotted on p-T diagram have the same enthaply.

2. A family of isenthalpes can be obtained for the gas.
a) true
b) false

Explanation: The initial pressure and temperature of gas are set to new values and we obtain a family of isenthalpes by throttling to different states.

3. The curve passing through the ____ of the isenthalpes is called the inversion curve.
a) minima
b) maxima
c) both of the mentioned
d) none of the mentioned

Explanation: The maxima is considered here for obtaining the inversion curve.

4. Which of the following statement is true?
a) the value of slope of an isenthalpe on the T-p diagram at any point is called the Joule-Kelvin coefficient
b) the region inside inversion curve is called the cooling region
c) the region outside inversion curve is called the heating region
d) all of the mentioned

Explanation: The region depends on the Joule-Kelvin coefficient on the T-p diagram.

5. The locus of all points at which the Joule-Kelvin coefficient is ____ is the inversion curve.
a) negative
b) positive
c) zero
d) infinity

Explanation: The inversion curve passes through the maxima of the isenthalpes and the value of Joule-Kelvin coefficient is zero there.

6. The region inside the inversion curve has ____ Joule-Kelvin coefficient and the region outside the inversion curve has ____ Joule-Kelvin coefficient.
a) positive, positive
b) negative, negative
c) negative, positive
d) positive, negative

Explanation: The region having positive Joule-Kelvin coefficient is called the cooling region and the one having negative Joule-Kelvin coefficient is called the heating region.

7. When an ideal gas is made to undergo a Joule-Kelvin expansion, i.e., throttling, there is no change in temperature.
a) true
b) false

Explanation: For an ideal gas, the value of Joule-Kelvin coefficient comes out to be zero.

8. For a gas being throttled, the change in temperature can be
a) positive
b) negative
c) zero
d) all of the mentioned

Explanation: The change in temperature depends upon the final pressure after throttling.

9. Maximum temperature drop occurs if the initial state lies ____ the inversion curve.
a) above
b) on
c) below
d) all of the mentioned

Explanation: This can be explained from the diagram fro maximum cooling by Joule-Kelvin expansion.

10. For an ideal gas,
a) volume expansivity = T and Joule-Kelvin coefficient = 0
b) volume expansivity = (1/T) and Joule-Kelvin coefficient = 1
c) volume expansivity = (1/T) and Joule-Kelvin coefficient = 0
d) volume expansivity = T and Joule-Kelvin coefficient = 1 