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 7 of 15
121. When the amount of work done is 333 cal and internal energy is 167 cal then heat supplied is _.
- A. 167 cal
- B. 175 cal
- C. 500 cal
- D. 600 cal
Explanation: By the first law of thermodynamics, the total energy of a system remains constant, and it can be converted from one form to another.
Correct answer: 500 cal- A. All real engines are less efficient than Carnot engine
- B. All real engines are less efficient due to friction and heat losses
- C. Efficiency of Carnot engine working between same two temperatures, depends on the nature of working substance
- D. The larger the temperature difference of two reservoirs, the greater is the efficiency.
Explanation: Option C is correct since it's the only incorrect statement as the efficiency of a 'Carnot engine' depends solely on the temperatures of…
Correct answer: Efficiency of Carnot engine working between same two temperatures, depends on the nature of working substance- A. Oscillation
- B. Vibration
- C. Cycle
- D. Circle
Explanation: In the context of thermodynamics, physics, and engineering, a "cycle" refers to a series of processes or events that brings a system back…
Correct answer: Cycle- A. Hot reservoir is at 0K
- B. Hot reservoir is at OC
- C. Cold reservoir is at 0C
- D. Cold reservoir is at 0K
Explanation: Efficiency of carnot engine= (1-T2/T1)*100T2=cold reservoir temp.T1=hot reservoir temp.If = (1-0/T2)*100=(1-0)*100=1*100Efficiency = 100%
Correct answer: Cold reservoir is at 0K- A. 0.25
- B. 75%
- C. 1
- D. Impossible to determine
Explanation: If work is 15J out of 60J, then 45J is expelled to the cold reservoir, which is 45/60×100, thus 75%.
Correct answer: 75%- A. 19.1 kJ
- B. 25.2 kJ
- C. 25 kJ
- D. Zero
Explanation: Correct Option:ATo determine the internal energy, we need to apply the First Law of Thermodynamics, which states that the change in…
Correct answer: 19.1 kJ- A. Total heat
- B. Work done
- C. Entropy
- D. Internal energy
Explanation: Correct Option:DThis option is correct because an isothermal process is the process in which temperature remains constant.
Correct answer: Internal energy- A. Work is done by the gas
- B. Internal energy of gas increases
- C. Both a and b
- D. None of them
Explanation: An isobaric process occurs at constant pressure. According to the first law of thermodynamics, the heat added to the system is used to do…
Correct answer: Both a and b- A. 100% efficiency
- B. Highest efficiency
- C. An efficiency which depends on the nature of substance
- D. None of these options are correct
Explanation: The statement "An ideal reversible heat engine has 100 percent efficiency" aligns with the principles of the Carnot heat engine, an…
Correct answer: 100% efficiency- A. ΔU = 0
- B. ΔU = negative
- C. ΔU = positive
- D. ΔW = 0
Explanation: An adiabatic system is an isolated system where no heat transfer takes place.
Correct answer: ΔU = negative- A. Change in pressure
- B. Change in temperature
- C. Change in volume
- D. All of these options are correct
Explanation: Since no thermal energy is taken in or given out in an adiabatic process, ΔQ = 0.
Correct answer: Change in temperature- A. 20%
- B. 25%
- C. 4%
- D. 50%
Explanation: Total input energy = 100 + 400 = 500 J. Therefore % efficiency which is (Useful Work Done/Total Energy Input) x 100 = 100/500 x 100 = 20.
Correct answer: 20%133. When the rate of a gas changes without a change in temperature, the gas is said to haveundergone:
- A. Isothermal Process
- B. Adiabatic Process
- C. Isochoric Process
- D. Isobaric Process
Explanation: An isothermal process is one in which there is no change in temperature.
Correct answer: Isothermal Process- A. Q/W
- B. Q - W
- C. W/Q
- D. 1 + Q/W
Explanation: The 1st law of thermodynamics is given by the equation:∆Q=∆U+∆W Where,∆Q is the heat supplied to the system ∆U is the change in internal…
Correct answer: Q - W- A. 100%
- B. 25%
- C. 50%
- D. 75%
Explanation: The percentage efficiency of a heat engine is given by:Efficiency = (Useful work output / Heat input) x 100%According to the second law of…
Correct answer: 75%- A. Q = W
- B. Q = ∆U
- C. Q= U + W
- D. W = -∆U
Explanation: The First law of thermodynamics is written as:∆Q = ∆U + ∆WIn adiabatic conditions, ∆Q = 0This is because adiabatic conditions imply that…
Correct answer: W = -∆U- A. In system A
- B. In system B
- C. Cannot be predicted
- D. Change is zero in both. (both are cyclic)
Explanation: In a cyclic process, the system undergoes a series of changes and returns to its initial state.
Correct answer: Change is zero in both. (both are cyclic)- A. Option A
- B. Option B
- C. Option C
- D. Option D
Explanation: Adiabatic expansion and compression are characterized by a more rapid change in pressure and volume.
Correct answer: Option A- A. 27 0C
- B. 127 0C
- C. 300 0 C
- D. 600 0 C
Explanation: 327k means 327-273-54 degrees celsius. For a reservoir to work at a 50% efficiency, the low reservoir must have half the temperature than…
Correct answer: 27 0C- A. Change in volume
- B. Change in temperature and volume
- C. Change in temperature
- D. Path followed to change internal energy
Explanation: The internal energy of an ideal gas depends solely on its temperature. According to the ideal gas law and the kinetic theory of gases, the…
Correct answer: Change in temperature