Previous Year Thermodynamics Objective Questions Answers

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6. When a system undergoes a process such that ∫ dQ/T = 0 and ΔS > 0, the process is called –

A. Reversible Adiabatic

B. Irreversible Adiabatic

C. Isobaric

D. Isothermal

Click for Answer/Explanation

Correct Answer is B

Irreversible Adiabatic

Δs = ∫ dQ/T + S (generated)

Now, ∫ dQ/T = 0 implies adiabatic & Δs > 0 implies irreversible

Note- For basic definitions search the keywords

Read Also- Fluid Mechanics: Objective Questions

7. A heat engine receives 1000 kW of heat at a constant temperature of 285 °C and rejects 492 kW of heat at 5 °C. Consider the following thermodynamic cycles in this regard –

  1. Carnot Cycle
  2. Reversible Cycle
  3. Irreversible Cycle

Now, tell which of these cycles could be executed by the engine?

A. 1 only

B. 2 only

C. 3 only

D. None of these (1, 2, or 3)

Click for Answer/Explanation

Correct Answer is D

The efficiency of an engine (or any cycle) can’t be more than a Carnot cycle or Carnot engine.

η (Carnot) = 50.18%

η (engine) = 50.8%

8. The cyclic integral of (δQ – δW) for a process is

A. Positive

B. Zero

C. Negative

D. Unpredictable

Click for Answer/Explanation

Correct Answer is B

δQ – δW = 0, From 1st Law of thermodynamics for a closed system

9. The throttling of certain gases may be used for getting the refrigeration effect. The value of the Joule-Thompson coefficient (μ) for such a throttling process is –

A. μ = 0

B. μ = 1

C. μ < 1

D. μ > 1

Click for Answer/Explanation

Correct Answer is D

For Refrigeration Effect μ > 1.

10. The correct relationship defining the Helmholtz Function?

A. F = U – TS

B. F = H – TS

C. F = U + TS

D. F = H + TS

Click for Answer/Explanation

Correct Answer is A

F = U – TS

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