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 13 of 15
- A. ΔW=ΔQ+ΔU
- B. ΔU=ΔW-ΔQ
- C. ΔQ=ΔW-ΔU
- D. ΔQ=ΔU-ΔW
- E. ΔU = ΔQ-ΔW
Explanation: Option E is the correct representation of first law of thermodynamics.
Correct answer: ΔU = ΔQ-ΔW- A. Heat flows out of the system
- B. Work is done by the system
- C. Work is done by the surrounding
- D. The potential energy of the system is changing
Explanation: By first law of Thermodynamics, Q= U + WQ= heat energy supplied to the systemU= internal energyW= Work done by the systemIf work is done…
Correct answer: Work is done by the system- A. Work
- B. Entropy
- C. Heat
Explanation: As the first law of thermodynamics is given byΔU = ΔQ - ΔWwhere ΔU is the change in internal energyΔQ is the heat addedand ΔW is the work…
Correct answer: Heat- A. nR/(y-1)(T1-T2)
- B. nR/(y-1)(T2-T1)
- C. nR(T2-T1)
- D. R(T2-T1)
Explanation: Option A is correct since it gives the correct statement for the work done in an adiabatic process.Option B is incorrect since it does not…
Correct answer: nR/(y-1)(T1-T2)- A. It is sum of all forms of molecular energies of a system
- B. It is proportional to translational K.E of the molecules
- C. It is a state function of a system
- D. All are correct
Explanation: All options are related to internal energy. Internal energy of a system with well defined boundaries, is the total of the kinetic energy…
Correct answer: All are correct- A. 8200J
- B. 5600J
- C. 7900J
- D. 6400J
Explanation: The change in internal energy (∆U) of a system can be found using the First Law of Thermodynamics: ∆U = ∆Q - ∆W, where ∆Q is the heat…
Correct answer: 7900J- A. T increases
- B. Mechanical energy comes into the system
- C. ∆Q= Zero
- D. All of these
Explanation: The correct answer is D because during an adiabatic contraction:A) The temperature (T) of the system increases.B) Mechanical energy comes…
Correct answer: All of these- A. The heating of a system equal to the increase of its internal energy plus the work done on the system
- B. The increase in the internal energy of a system equal to the heating of the system minus the work done by the system
- C. The increase in the internal energy of system equal to the heating of the system plus the work done by the system
- D. The work done on a system equals the increase of its theramal energy plus the heating of the system
Explanation: Statement of first law of thermodynamics states the increase in the internal energy of a system equal to the heating of the system minus…
Correct answer: The increase in the internal energy of a system equal to the heating of the system minus the work done by the system- A. 31.4J
- B. 3.14 x 10^6J
- C. 3.14J
- D. None
Explanation: Q=∆U+W cyclic process i.e. ∆U=0 Q=W=Area pf P-V graph= πr² =π(Pr)(Vr) =3.14(100x103)(100)=31.4x106 J
Correct answer: 3.14 x 10^6J- A. -100J
- B. 0 J
- C. +100 J
- D. None
Explanation: The correct answer is C because in an adiabatic process, there is no heat exchange (Q = 0) between the gas and its surroundings.
Correct answer: +100 J- A. Isothermal expansion
- B. Energy dissipiation
- C. Adiabatic expansion
- D. Adiabatic compression
Explanation: Adiabatic expansion is a type of expansion in which no heat is exchanged with the surroundings.
Correct answer: Adiabatic expansion- A. Must remain same
- B. May fall
- C. May rise
- D. Both B & C
Explanation: If heat neither enters nor leaves a system, then its temperature may rise or may fall.
Correct answer: Both B & C- A. Increases.
- B. Decreases.
- C. Remains constant.
- D. Varies unpredictably.
Explanation: In an isothermal process, the temperature of the system remains constant.
Correct answer: Remains constant.- A. I only.
- B. III only.
- C. II or III.
- D. I or III.
Explanation: In a Carnot cycle, the working substance undergoes a series of processes that eventually return it to its initial state, which implies the…
Correct answer: I or III.- A. Sink only.
- B. Source only.
- C. Surrounding.
- D. Source and sink.
Explanation: The efficiency of a Carnot engine is determined by the temperatures of both the heat source (T1) and the heat sink (T2).
Correct answer: Source and sink.- A. Adiabatic expansion
- B. Isothermal expansion
- C. Adiabatic compression
- D. Isothermal compression
Explanation: The correct answer is Adiabatic expansion. In this process, the system does work on the surroundings without any heat exchange, leading to…
Correct answer: Adiabatic expansion- A. Depends on the path taken to reach a state
- B. Independent of the path taken to reach a state
- C. Always increasing in a closed system
- D. Dependent only on external factors
Explanation: In thermodynamics, internal energy is a state function, meaning it is determined by the state of the system and is independent of the path…
Correct answer: Independent of the path taken to reach a state- A. Increases
- B. Decreases
- C. Remains the same
- D. Varies unpredictably
Explanation: The efficiency of a Carnot engine is calculated using the formula: efficiency = 1 - (T_sink / T_source), where T_sink and T_source are the…
Correct answer: Decreases- A. Decrease in energy in the system.
- B. Increase in energy in the surrounding.
- C. Unavailability of energy in the system.
- D. Degradation of energy in the environment.
Explanation: Entropy is a concept from thermodynamics often described as a measure of disorder or randomness.
Correct answer: Unavailability of energy in the system.- A. equal to 0 K.
- B. less than 0 K.
- C. equal to its input temperature.
- D. less than its input temperature.
Explanation: To achieve 100% efficiency, a heat engine would require its output temperature (cold reservoir temperature) to be at absolute zero (0 K).
Correct answer: equal to 0 K.