Free First Law of Thermodynamics MCQs with Answers
297 First Law of 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.
The first law relates heat supplied, work done and the change in internal energy through energy conservation. Problems use sign conventions and apply the law to isothermal, adiabatic, isobaric and isochoric processes. Internal energy is a state function, while heat and work depend on the path followed.
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297 questions · page 4 of 15
- A. nRT ln(V₂/V₁)
- B. nRT (V₂/V₁)
- C. nR ln(T₂/T₁)
- D. nRT (T₂/T₁)
Explanation: For an isothermal process, the work done by an ideal gas is W = nRT ln(V₂/V₁), where n is moles, R is the gas constant, T is constant…
Correct answer: nRT ln(V₂/V₁)- A. Zero
- B. Positive
- C. Negative
- D. Equal to heat supplied
Explanation: In an adiabatic expansion, the gas does work on the surroundings, so work done by the gas is positive, and its internal energy decreases…
Correct answer: Positive- A. Pressure only
- B. Volume only
- C. Temperature only
- D. Pressure and volume
Explanation: For an ideal gas, internal energy is a function of temperature only, as U = (f/2)nRT, where f is degrees of freedom, n is moles, R is the…
Correct answer: Temperature only- A. Positive
- B. Negative
- C. Zero
- D. Equal to work done
Explanation: In isothermal process, temperature of ideal gas remains constant, its internal energy, depend only on temperature (U =(f/2)nRT), does not…
Correct answer: Zero- A. Change in internal energy
- B. Work done
- C. Change in pressure
- D. Change in temperature
Explanation: In an isochoric process, volume is constant, so no work is done (W = PΔV = 0).
Correct answer: Change in internal energy- A. PV = constant
- B. P/V = constant
- C. PVᵞ = constant
- D. PᵞV = constant
Explanation: In an adiabatic process, the relation for an ideal gas is PV^γ = constant, where γ is the ratio of specific heats (Cp/Cv), distinguishing…
Correct answer: PVᵞ = constant- A. 200 J
- B. 800 J
- C. -200 J
- D. 500 J
Explanation: By the first law of thermodynamics, ΔU = Q - W, where Q = 500 J (heat absorbed) and W = 300 J (work done by the system).
Correct answer: 200 J- A. Heat is added to the system
- B. Work is done on the gas
- C. Volume remains constant
- D. Pressure decreases
Explanation: In adiabatic compression, no heat is exchanged (Q = 0), and work is done on the gas, increasing its internal energy (ΔU = - W), which…
Correct answer: Work is done on the gas- A. TVᵞ = constant
- B. TᵞV = constant
- C. TV⁽ᵞ⁻¹⁾ = constant
- D. T/V = constant
Explanation: For an adiabatic process, PV^γ = constant. Using the ideal gas law (PV = nRT), this becomes TV^(γ-1) = constant, where γ is the ratio of…
Correct answer: TV⁽ᵞ⁻¹⁾ = constant- A. UII > ΔUI
- B. UI = ΔUII
- C. UII < ΔUI
- D. Relation between ΔUI and ΔUII cannot be determined
Explanation: As internal energy is a state function therefore change in internal energy does not depends upon the path followed i.e. ΔUI=Δ UII
Correct answer: UI = ΔUII- A. Q = U
- B. U = W
- C. W = U/W
- D. Q = W
Explanation: Since it is an isothermal process, there is no change in temperature hence the internal energy is constant.
Correct answer: Q = W- A. Isothermal process
- B. Adiabatic compression
- C. Isobaric expansion
- D. Isochoric cooling
Explanation: In adiabatic compression, work done on gas with no heat exchange (Q=0), increasing its internal energy and its temperature.
Correct answer: Adiabatic compression- A. Zero
- B. Equal to net heat transfer
- C. Equal to internal energy change
- D. Always positive
Explanation: In a cyclic process, the system returns to its initial state, so ΔU = 0.
Correct answer: Equal to net heat transfer- A. nRΔT
- B. (P₁V₁ - P₂V₂)/(γ - 1)
- C. nRT ln(V₂/V₁)
- D. PΔV
Explanation: For an adiabatic process, work done is W = (P₁V₁ - P₂V₂)/(γ - 1), derived from the pressure-volume relationship and the first law, where γ…
Correct answer: (P₁V₁ - P₂V₂)/(γ - 1)- A. The temperature of the cold reservoir increases
- B. The temperature of the hot reservoir decreases
- C. The temperature difference between reservoirs increases
- D. The pressure of the gas increases
Explanation: Carnot efficiency is η = 1 - (Tcold/Thot). Increasing the temperature difference (higher Thot or lower Tcold) increases efficiency.
Correct answer: The temperature difference between reservoirs increases- A. 1st Law of thermodynamics
- B. 2nd Law of thermodynamics
- C. Law of conservation of energy
- D. Law of entropy
Explanation: An adiabatic process is one where no heat enters or leaves a system. Here, we compress a gas adiabatically inside a bicycle pump.
Correct answer: 1st Law of thermodynamics- A. At constant temperature: Q = -W
- B. When no work is done: ΔU = Q
- C. In gaseous system: ΔU = Q + P Δ V
- D. When work is done by the system: ΔU = Q - W
Explanation: There are two sign conventions:1. ∆U= Q+W: Here, work done BYthe gas/system is taken POSITIVE. 2.
Correct answer: When work is done by the system: ΔU = Q - W- A. 22.3%
- B. 20.0%
- C. 23.6%
- D. 30.6%
- E. 33.6%
Explanation: The efficiency of a Carnot engine is calculated using the formula η% = (1 - T2/T1) × 100%, where T1 is the temperature of the hot…
Correct answer: 23.6%- A. 600 Joules
- B. 900 Joules
- C. 300 Joules
- D. 400 Joules
- E. 1600 Joules
Explanation: Change in internal energy of the system is given by:Change in internal energy = Heat absorbed - Work done - Heat lostChange in internal…
Correct answer: 300 Joules- A. Isothermal process
- B. Adiabatic process
- C. Isochoric process
- D. Isobaric process
- E. Carnot cycle
Explanation: For equation ΔU = ΔQ + W to be ΔU = ΔQ, the work done should be equal to 0.
Correct answer: Isochoric process