Are you preparing for mechanical engineering exams, competitive tests like GATE/IES, or just want to strengthen your thermodynamics basics? Here’s a curated set of 10 important thermodynamics MCQs with answers and explanations.
Table of Contents
Thermodynamics MCQs – Set 1
1. Which law of thermodynamics defines entropy?
a) First Law
b) Second Law ✅
c) Third Law
d) Zeroth Law
Explanation: The second law introduces entropy as a measure of disorder in a system.
2. In cryogenics, liquid nitrogen boils at:
a) 77 K ✅
b) 90 K
c) 4.2 K
d) 273 K
Explanation: Liquid nitrogen has a boiling point of 77 Kelvin, making it a common cryogenic fluid.
3. The unit of heat transfer coefficient is:
a) W/m²K ✅
b) J/kg
c) Pa
d) W/K
Explanation: Heat transfer coefficient relates heat flow rate to surface area and temperature difference.
4. Zeroth law of thermodynamics establishes the concept of:
a) Heat
b) Work
c) Temperature ✅
d) Pressure
Explanation: It states that if two systems are each in thermal equilibrium with a third system, they are in thermal equilibrium with each other.
5. For an ideal gas, internal energy depends on:
a) Volume only
b) Pressure only
c) Temperature only ✅
d) Both pressure and volume
Explanation: For an ideal gas, internal energy is a function of temperature only.
6. Carnot cycle efficiency depends on:
a) Working fluid
b) Temperature of source and sink ✅
c) Pressure ratio
d) Specific heat of fluid
7. COP of a refrigerator is:
a) Always less than 1
b) Greater than 1 ✅
c) Equal to 1
d) Can’t be defined
8. In an isothermal process for an ideal gas:
a) Pressure remains constant
b) Temperature remains constant ✅
c) Volume remains constant
d) None of these
9. Work done in an isothermal process is given by:
a) W = nCvΔT
b) W = nRT ln(V2/V1) ✅
c) W = PdV
d) W = 0
10. Entropy change in an irreversible adiabatic process is:
a) Positive ✅
b) Zero
c) Negative
d) Infinite
Explanation: Entropy always increases in irreversible processes.