THERMODYNAMICS MCQ SET 8
Q1. The COP of a refrigerator is related to the COP of a heat pump by:
A) COP_HP = COP_R + 1
B) COP_HP = COP_R โ 1
C) COP_HP = 1 โ COP_R
D) COP_HP = 1/COP_R
Answer: A) COP_HP = COP_R + 1
Explanation: Since both use the same principle, the heat pumpโs COP is one unit higher than that of the refrigerator.
Q2. The process which occurs without any heat or mass transfer to the surroundings is called:
A) Adiabatic process
B) Isolated process
C) Reversible process
D) Quasi-static process
ย Answer: B) Isolated process
Explanation: In an isolated process, there is no exchange of energy or mass with the surroundings.
Q3. The performance of a heat engine is measured by:
A) COP
B) Efficiency
C) Enthalpy
D) Entropy
Answer: B) Efficiency
Explanation: Efficiency = Work output / Heat supplied ร 100%.
Q4. The heat added at constant pressure equals the change in:
A) Internal energy
B) Enthalpy
C) Entropy
D) Work
Answer: B) Enthalpy
Explanation: At constant pressure, ฮH = Q.
Q5. When a system absorbs 500 J of heat and does 200 J of work, the change in internal energy is:
A) 700 J
B) 500 J
C) 300 J
D) 200 J
Answer: C) 300 J
Explanation: From the first law, ฮU = Q โ W = 500 โ 200 = 300 J.
Q6. The process used in the condenser of a steam power plant is:
A) Expansion
B) Compression
C) Condensation
D) Evaporation
Answer: C) Condensation
Explanation: In the condenser, exhaust steam from the turbine is condensed into water by rejecting heat to the cooling medium.
Q7. The measure of a heat engineโs performance is given by:
A) Entropy
B) Efficiency
C) COP
D) Enthalpy
Answer: B) Efficiency
Explanation: Efficiency shows how effectively a heat engine converts heat into useful work.
Q8. The property of a system that indicates the amount of useful work obtainable is:
A) Enthalpy
B) Entropy
C) Availability (Exergy)
D) Free energy
Answer: C) Availability (Exergy)
Explanation: Exergy measures the maximum useful work that can be obtained from a system.
Q9. A process which occurs at constant enthalpy is called:
A) Isenthalpic process
B) Isochoric process
C) Isobaric process
D) Isothermal process
Answer: A) Isenthalpic process
Explanation: Throttling and Joule-Thomson processes are examples of isenthalpic processes.
Q10. The air-standard cycle for a petrol engine is:
A) Diesel cycle
B) Otto cycle
C) Brayton cycle
D) Rankine cycle
Answer: B) Otto cycle
Explanation: Petrol engines work on the Otto cycle, involving two isentropic and two constant-volume processes.
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