THERMODYNAMICS MCQ SET 6
Q1. The efficiency of a Carnot engine increases when:
A) Source temperature increases
B) Sink temperature increases
C) Source temperature decreases
D) Both increase equally
Answer: A) Source temperature increases
Explanation: Carnot efficiency = 1 โ (Tโ/Tโ). Increasing Tโ (source temperature) improves efficiency.
Q2. The Kelvin-Planck and Clausius statements are:
A) Contradictory
B) Equivalent
C) Independent
D) Unrelated
Answer: B) Equivalent
Explanation: Both are different expressions of the second law of thermodynamics.
Q3. The change in entropy for a reversible adiabatic process is:
A) Positive
B) Negative
C) Zero
D) Infinite
Answer: C) Zero
Explanation: For a reversible adiabatic (isentropic) process, entropy remains constant.
Q4. The specific heat of a substance depends on:
A) Mass only
B) Nature of substance and temperature
C) Volume only
D) Pressure only
Answer: B) Nature of substance and temperature
Explanation: Different substances require different amounts of heat to change temperature.
Q5. The energy required to change water into steam at constant temperature is called:
A) Latent heat of fusion
B) Latent heat of vaporization
C) Sensible heat
D) Specific heat
ย Answer: B) Latent heat of vaporization
Explanation: Itโs the heat needed to convert liquid to vapor without temperature change.
Q6. In a gas turbine, the working cycle is:
A) Rankine cycle
B) Otto cycle
C) Brayton cycle
D) Diesel cycle
Answer: C) Brayton cycle
Explanation: Gas turbines operate on the Brayton (or Joule) cycle.
Q7. The process used in steam nozzles is:
A) Isothermal expansion
B) Isentropic expansion
C) Isobaric expansion
D) Isochoric process
Answer: B) Isentropic expansion
Explanation: Steam expands adiabatically and reversibly in a nozzle.
Q8. The efficiency of a reversible engine depends on:
A) Working substance
B) Pressure
C) Temperature limits
D) Type of process
Answer: C) Temperature limits
Explanation: Reversible engine efficiency = 1 โ (Tโ/Tโ).
Q9. When a gas expands adiabatically, its temperature:
A) Increases
B) Decreases
C) Remains constant
D) Doubles
Answer: B) Decreases
Explanation: In adiabatic expansion, gas does work and loses internal energy, lowering temperature.
Q10. The process in which no work is done is:
A) Isothermal
B) Isochoric
C) Isobaric
D) Adiabatic
Answer: B) Isochoric
Explanation: At constant volume, there is no displacement work.
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