Thermodynamics – Objective Questions

Page 6 : Graphs, Cycles & Visual Reasoning

Q51. Area under a P–V graph represents:

  • A) Heat supplied
  • B) Internal energy change
  • C) Work done
  • D) Entropy change

Answer: C

Explanation: Work done = ∫P dV = area under curve.

Q52. A closed loop on P–V diagram represents:

  • A) Isochoric process
  • B) Isothermal process
  • C) Cyclic process
  • D) Adiabatic process

Answer: C

Explanation: System returns to initial state.

Q53. Direction of cycle on P–V diagram is clockwise. Net work is:

  • A) Zero
  • B) Negative
  • C) Positive
  • D) Depends on gas

Answer: C

Explanation: Clockwise cycle ⇒ gas does work.

Q54. Which curve is steeper on a P–V diagram?

  • A) Isothermal
  • B) Adiabatic
  • C) Isochoric
  • D) Isobaric

Answer: B

Explanation: Adiabatic drops pressure faster than isothermal.

Q55. On T–V diagram, which process is a straight line?

  • A) Isothermal
  • B) Isochoric
  • C) Isobaric
  • D) Adiabatic

Answer: C

Explanation: From PV = nRT ⇒ T ∝ V at constant P.

Q56. Which graph gives direct information about entropy change?

  • A) P–V
  • B) T–S
  • C) P–T
  • D) V–T

Answer: B

Explanation: Area under T–S curve = heat.

Q57. In a P–V diagram, vertical line represents:

  • A) Isothermal
  • B) Isobaric
  • C) Isochoric
  • D) Adiabatic

Answer: C

Explanation: Volume constant.

Q58. In T–S diagram, vertical line means:

  • A) Isochoric
  • B) Isothermal
  • C) Adiabatic
  • D) Isobaric

Answer: C

Explanation: Entropy constant ⇒ reversible adiabatic.

Q59. Net heat absorbed in a complete cycle equals:

  • A) Change in internal energy
  • B) Zero
  • C) Net work done
  • D) Enthalpy change

Answer: C

Explanation: ΔU = 0 ⇒ Q = W

Q60. Which diagram best represents Carnot cycle?

  • A) Rectangle on P–V
  • B) Closed loop with two isotherms and two adiabats
  • C) Triangle on T–V
  • D) Straight line on P–T

Answer: B

Explanation: Carnot cycle = 2 isothermal + 2 adiabatic processes.

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