Free Thermodynamics MCQs with Answers
714 Thermodynamics MCQs from Physics, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
Thermal equilibrium and heat explain how temperature and energy transfer are related, while molar specific heats describe the heat required by a gas at constant volume or constant pressure. The first law connects heat supplied, work done and change in internal energy, with sign conventions kept distinct from temperature changes.
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Read the Thermodynamics notesFree MDCAT chapter notes with key terms714 questions · page 5 of 36
- A. Isothermal change
- B. Adiabatic change
- C. Isobaric change.
- D. Isochoric change
Explanation: The Laplace formula is related to the adiabatic process in thermodynamics.
Correct answer: Adiabatic change- A. Isobaric process
- B. Adiabatic process
- C. Isothermal process
- D. Isochoric process
Explanation: An isochoric process is a thermodynamic process that occurs at constant volume.
Correct answer: Isochoric process- A. First law of thermodynamics
- B. Second law of thermodynamics
- C. Newton's laws of motion
- D. Entropy
Explanation: A refrigerator operates on the principles of the second law of thermodynamics.
Correct answer: Second law of thermodynamics- A. There will be a change in internal energy
- B. There will be a change in temperature
- C. There will be no change in internal energy
- D. The external pressure will increase
Explanation: This describes a free expansion process into a vacuum. Since no external pressure is overcome, the work done (W) is zero.
Correct answer: There will be no change in internal energy- A. Increased by 80 joules
- B. Decreased by 80 joules
- C. Increased by 20 joules
- D. Decreased by 20 joules
Explanation: Using the first law of thermodynamics, ΔU = Q - W. Here, heat flows in, so Q = +30 J, and the system does work, so W = +50 J.
Correct answer: Decreased by 20 joules- A. W = ΔU = Q
- B. Q = -W
- C. Q = W
- D. W = -ΔU
Explanation: The first law of thermodynamics states that the ΔU = Q - W.Adiabatic Process: An adiabatic process is defined as a thermodynamic process…
Correct answer: W = -ΔU- A. 150 J
- B. 300 J
- C. 250 J
- D. 500 J
Explanation: According to the first law of thermodynamics, ΔU = Q - W. Heat is supplied, so Q = +400 J, and work is done by the system, so W = +150 J.
Correct answer: 250 J- A. Isochoric
- B. Isobaric
- C. Isothermal
- D. Isentropic
Explanation: For an ideal gas, internal energy is a function of temperature. In an isothermal process, the temperature is constant (ΔT = 0), so the…
Correct answer: Isothermal89. In which process the entire heat supplied to the gas is converted to the internal energy of the gas?
- A. Isochoric process
- B. Isobaric process
- C. Isothermal process
- D. Adiabatic process
Explanation: For all heat supplied (Q) to be converted into internal energy (ΔU), the work done (W) must be zero.
Correct answer: Isochoric process- A. Decreases
- B. Increases
- C. Becomes zero
- D. Remains constant
Explanation: For an ideal gas, internal energy depends only on its temperature. Since an isothermal process occurs at a constant temperature by…
Correct answer: Remains constant- A. Positive in each case
- B. Negative for I and positive for II
- C. Positive for I and negative for II
- D. Zero in I and positive for II
Explanation: An adiabatic process, has no heat transfer (Q=0). For an isothermal expansion, the internal energy does not change (ΔU=0), but the gas…
Correct answer: Zero in I and positive for II92. The heat rejected by a Carnot engine operating between 600 K and 300 K with 2000 J of heat input is:
- A. 1000 J
- B. 1500 J
- C. 600 J
- D. 1200 J
Explanation: Efficiency of a Carnot engine is η = 1 - (Tcold /Thot ) = 1 - (300/600) = 0.5. Work done is W = η × Qin = 0.5 × 2000 = 1000 J.
Correct answer: 1000 J- A. 4.00
- B. 1.00
- C. 0.25
- D. Impossible to determine
Explanation: Thermal efficiency (η) is the ratio of useful work output to the total heat input (η = Work / Heatin).
Correct answer: 0.2594. The efficiency of a heat engine in terms of the temperature of the reservoir and sink is defined as:
- A. T₁/T₂
- B. 1+T₁/T₂
- C. 1-T₂/T₁
- D. T₂/T₁
Explanation: The maximum possible efficiency of a heat engine operating between a hot reservoir at temperature T₁ and a cold reservoir at temperature…
Correct answer: 1-T₂/T₁- A. PV = constant
- B. PVᵞ = constant
- C. P/V=RT/n
- D. PVy=nRT
Explanation: This is the mathematical relationship that describes an adiabatic process for an ideal gas.
Correct answer: PVᵞ = constant- A. Isothermal process
- B. Adiabatic process
- C. Neither of these options is correct.
- D. Equal in both cases
Explanation: For an expansion from the same initial state to the same final volume, the pressure in an isothermal process remains higher than in an…
Correct answer: Isothermal process- A. 20%
- B. 25%
- C. 4%
- D. 50%
Explanation: From the conservation of energy, the heat input (Q₁) must equal the work done (W) plus the heat rejected (Q₂).
Correct answer: 20%- A. Slow compression of an elastic spring
- B. Slow evaporation of a substance in an isolated vessel
- C. Slow compression of a gas
- D. A chemical explosion
Explanation: An irreversible process is one that cannot return to its initial state along the same path.
Correct answer: A chemical explosion- A. Change in pressure
- B. Change in temperature
- C. Change in volume
- D. All of these are correct
Explanation: In an adiabatic process, there is no heat exchange (Q=0), so first law of thermodynamics becomes ΔU = -W.
Correct answer: Change in temperature- A. 80°C, 37°C
- B. 99°C, 30°C
- C. 99°C, 25°C
- D. 99°C, 37°C
Explanation: The initial efficiency is η = 1/6 = 1 - Tsink /Tsource . When the sink temperature becomes Tsink - 62, the new efficiency is 2(1/6) = 1/3.
Correct answer: 99°C, 37°C