THERMODYNAMICS MCQ SET 10
Q1. The performance of a refrigerator decreases when:
A) Condenser temperature increases
B) Evaporator temperature increases
C) COP increases
D) Compression ratio decreases
Answer: A) Condenser temperature increases
Explanation: Higher condenser temperature reduces the temperature difference, lowering efficiency.
Q2. For real gases, deviations from ideal behavior occur at:
A) Low pressure and high temperature
B) High pressure and low temperature
C) Low pressure and low temperature
D) High pressure and high temperature
Answer: B) High pressure and low temperature
Explanation: Under these conditions, intermolecular forces become significant.
Q3. The term โenthalpy of vaporizationโ means:
A) Heat required to evaporate a unit mass
B) Heat required to heat the vapor
C) Heat required to melt solid
D) Heat required to raise temperature by 1ยฐC
Answer: A) Heat required to evaporate a unit mass
Explanation: It is the latent heat for the phase change from liquid to vapor.
Q4. The COP of a refrigerator operating between 300 K and 250 K is:
A) 1.5
B) 5
C) 6
D) 2
Answer: B) 5
Explanation: COP = TL / (TH โ TL) = 250 / (300 โ 250) = 5.
Q5. A process in which the product of pressure and volume remains constant is known as:
A) Isothermal process
B) Polytropic process
C) Adiabatic process
D) Isochoric process
Answer: A) Isothermal process
Explanation: For isothermal changes, PV = constant.
Q6. When heat is added to a system and no work is done, the change is in:
A) Pressure
B) Volume
C) Internal energy
D) Temperature only
Answer: C) Internal energy
Explanation: By the first law, ฮU = Q (if W = 0).
Q7. The first law of thermodynamics does not provide information about:
A) Energy conservation
B) Direction of process
C) Heat-work relation
D) Energy balance
Answer: B) Direction of process
Explanation: The first law deals with quantity, not direction, which is addressed by the second law.
Q8. During adiabatic compression of air, its:
A) Temperature decreases
B) Pressure decreases
C) Temperature increases
D) Volume increases
Answer: C) Temperature increases
Explanation: Compression increases internal energy, raising the temperature.
Q9. The concept of temperature was introduced by which law of thermodynamics?
A) Zeroth law
B) First law
C) Second law
D) Third law
Answer: A) Zeroth law
Explanation: The Zeroth law defines temperature and thermal equilibrium.
Q10. The entropy of the universe:
A) Increases continuously
B) Decreases continuously
C) Remains constant
D) Becomes zero
Answer: A) Increases continuously
Explanation: According to the second law, entropy of an isolated system (universe) always increases.
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