Explore topic-wise MCQs in Thermodynamics.

This section includes 156 Mcqs, each offering curated multiple-choice questions to sharpen your Thermodynamics knowledge and support exam preparation. Choose a topic below to get started.

1.

A car engine operates with a thermal efficiency of 35%. Assume the air-conditioner has a coefficient of performance of 3 working as a refrigerator cooling the inside using engine shaft work to drive it. How much fuel energy should be spend extra to remove 1 kJ from the inside?

A. 0.752 kJ
B. 0.952 kJ
C. 0.852 kJ
D. none of the mentioned
Answer» C. 0.852 kJ
Discussion
2.

In a cryogenic experiment you need to keep a container at -125°C although it gains 100 W due to heat transfer. What is the smallest motor you would need for a heat pump absorbing heat from the container and rejecting heat to the room at 20°C?

A. 97.84 kW
B. 98.84 kW
C. 99.84 kW
D. 95.84 kW
Answer» B. 98.84 kW
Discussion
3.

A cyclic machine, as shown below, receives 325 kJ from a 1000 K energy reservoir. It rejects 125 kJ to a 400 K energy reservoir and the cycle produces 200kJ of work as output. Is this cycle reversible, irreversible, or impossible?

A. reversible
B. irreversible
C. impossible
D. none of the mentioned
Answer» D. none of the mentioned
Discussion
4.

An air-conditioner provides 1 kg/s of air at 15°C cooled from outside atmospheric air at 35°C. Estimate the amount of power needed to operate the air-conditioner.

A. 1.09 kW
B. 1.19 kW
C. 1.29 kW
D. 1.39 kW
Answer» E.
Discussion
5.

A heat pump is used to meet the heating requirements of a house and maintain it at 20°C. On a day when the outdoor air temperature drops to 2°C, the house is estimated to lose heat at a rate of 80,000 kJ/h. If the heat pump under these conditions has a COP of 2.5, determine the rate at which heat is absorbed from the cold outdoor air.

A. 32000 kJ/h
B. 48000 kJ/h
C. 54000 kJ/h
D. 72000 kJ/h
Answer» C. 54000 kJ/h
Discussion
6.

A heat pump is used to meet the heating requirements of a house and maintain it at 20°C. On a day when the outdoor air temperature drops to 2°C, the house is estimated to lose heat at a rate of 80,000 kJ/h. If the heat pump under these conditions has a COP of 2.5, determine the power consumed by the heat pump.

A. 32000 kJ/h
B. 33000 kJ/h
C. 34000 kJ/h
D. 35000 kJ/h
Answer» B. 33000 kJ/h
Discussion
7.

The food compartment of a refrigerator is maintained at 4°C by removing heat from it at a rate of 360 kJ/min. If the required power input to the refrigerator is 2kW, determine the rate of heat rejection to the room that houses the refrigerator.

A. 450 kJ/min
B. 460 kJ/min
C. 470 kJ/min
D. 480 kJ/min
Answer» E.
Discussion
8.

The food compartment of a refrigerator is maintained at 4°C by removing heat from it at a rate of 360 kJ/min. If the required power input to the refrigerator is 2kW, determine the coefficient of performance of the refrigerator.

A. 4
B. 3
C. 2
D. 1
Answer» C. 2
Discussion
9.

A car engine with a power output of 50 kW has a thermal efficiency of 24 percent. Determine the fuel consumption rate of this car if the fuel has a heating value of 44,000 kJ/kg .

A. 0.00273 kg/s
B. 0.00373 kg/s
C. 0.00473 kg/s
D. 0.00573 kg/s
Answer» D. 0.00573 kg/s
Discussion
10.

Heat is transferred to a heat engine from a furnace at a rate of 80 MW. If the rate of waste heat rejection to a nearby river is 50 MW, determine the thermal efficiency for this heat engine.

A. 47.5 %
B. 27.5 %
C. 37.5 %
D. none of the mentioned
Answer» D. none of the mentioned
Discussion
11.

Heat is transferred to a heat engine from a furnace at a rate of 80 MW. If the rate of waste heat rejection to a nearby river is 50 MW, determine the net power output for this heat engine.

A. 30 MW
B. 40 MW
C. 50 MW
D. 60 MW
Answer» B. 40 MW
Discussion
12.

The second law of thermodynamics states that?

A. Entropy of an isolated system can never decrease over time
B. Entropy of a pure crystalline substance at 0K is 0
C. Energy is conserved
D. Entropy of a system can never decrease
Answer» B. Entropy of a pure crystalline substance at 0K is 0
Discussion
13.

Which of the following is the Kelvin Planck statement?

A. Heat from a cold reservoir cannot be transferred to a hot reservoir without external work
B. Efficiency for a reversible cyclic process can be 1
C. Heat from a hot reservoir can be completely converted into work if process is reversible
D. Efficiency of a heat engine is less than 1
Answer» E.
Discussion
14.

Which law of thermodynamics says that efficiency of a heat engine cannot be 1?

A. First
B. Zeroth
C. Second
D. Third
Answer» D. Third
Discussion
15.

According to the first law of thermodynamics, a book lying on a table can fly upwards on its own by using the internal energy of the table. True or False?

A. True
B. False
Answer» B. False
Discussion
16.

A process is carried out between 2 systems. It is possible for entropy of one system to decrease. True or False?

A. True
B. False
Answer» B. False
Discussion
17.

Heat is transferred to a heat engine from a furnace at a rate of 80 MW. If the rate of waste heat rejection to a nearby river is 50 MW, what is the net power output?

A. 130 MW
B. 1.6 MW
C. 16 MW
D. 30 MW
Answer» E.
Discussion
18.

Any change in entropy could be achieved by changing _____

A. heat
B. acceleration
C. velocity
D. mass
Answer» B. acceleration
Discussion
19.

For a thermodynamic process to be reversible, the temperature difference between the hot body and working substance should be _______.

A. Zero
B. Minimum
C. Maximum
D. Infinity
Answer» B. Minimum
Discussion
20.

One reversible heat engine operates between 1000 K and T K and another reversible heat engine operates between T and 400 K. if both heat engine have same heat input and output, the value of T is

A. 582.7 K
B. 632.5 K
C. 682.8 K
D. 732.5 K
Answer» C. 682.8 K
Discussion
21.

According to Kelvin-Planck’s statement of the second law of thermodynamics, which of the following statements is correct?

A. Heat from a source should be rejected to a high temperature sink.
B. It restricts the mechanical efficiency of the heat engine to be lesser than unity.
C. Thermal efficiency of the heat engine will be unity.
D. It restricts the thermal efficiency of the heat engine to be lesser than unity.
Answer» E.
Discussion
22.

An ideal, Carnot engine operates between reservoirs at temperature 20 °C and 200 °C. If 10 kW of power is produced, the rate at which heat is rejected is approximately:

A. 15.3 kJ/ s
B. 12.3 kJ/s
C. 14.3 kJ/s
D. 16.3 kJ/s
Answer» E.
Discussion
23.

A Reversed Carnot Engine removes 50 kW from a heat sink. The temperature of the heat sink is 250 K and the temperature of the heat reservoir is 300 K. The power required of the engine is:

A. 10 kW
B. 20 kW
C. 30 kW
D. 50 kW
Answer» B. 20 kW
Discussion
24.

If hot water and cold water are mixed, then the entropy of the system will

A. Increase
B. Decrease
C. Remains same
D. May increase/Decrease depending on initial temperature of hot water and cold water
Answer» B. Decrease
Discussion
25.

A heat engine working with a thermal efficiency of 35% receives 2 kW of heat from a furnace. The waste heat rejected from the engine is

A. 0.7 kW
B. 0.35 kW
C. 1.3 kW
D. 1.65 kW
Answer» D. 1.65 kW
Discussion
26.

Considering frictional effects, the isentropic fluid flow becomes:

A. irreversible adiabatic flow
B. perfect gas flow
C. ideal fluid flow
D. reversible adiabatic flow
Answer» B. perfect gas flow
Discussion
27.

For an ideal gas, a constant pressure line and a constant volume line intersect at a point, in the Temperature (T) versus specific entropy (S) diagram. Cp is the specific heat at constant pressure and Cv is the specific heat at constant volume. The ratio of the slopes of the constant pressure and constant volume lines at the point of intersection is

A. \(\frac{{Cp - Cv}}{{Cp}}\)
B. \(\frac{{{C_p}}}{{{C_v}}}\)
C. \(\frac{{{C_p} - {C_v}}}{{{C_v}}}\)
D. \(\frac{{{C_v}}}{{{C_p}}}\)
Answer» E.
Discussion
28.

An engine operates between temperature limits of 900 K and T2 and another between T2 and 400 K for both to be equally efficient T2 will be equal to.

A. 600 K
B. 650 K
C. 625 K
D. 700 K
Answer» B. 650 K
Discussion
29.

A cyclic heat engine operates between a source temperature of 800°C and a sink temperature of 30°C. The least rate of heat rejection per kW net output of engine will be nearly

A. 0.2 kW
B. 0.4 kW
C. 0.6 kW
D. 0.8 kW
Answer» C. 0.6 kW
Discussion
30.

If a heat engine produce work only by interacting with one source. What kind of machine is this?

A. Perpetual motion machine of first kind (PMM1)
B. Perpetual motion machine of second kind (PMM2)
C. Perpetual motion machine of third kind (PMM3)
D. None of these
Answer» C. Perpetual motion machine of third kind (PMM3)
Discussion
31.

1 kJ heat is transferred to the surroundings from a reservoir at a temperature of 527°C. The change in entropy of the reservoir is:

A. – 0.8 J/K
B. + 0.8 J/K
C. – 1.25 J/K
D. 1.25 J/K
Answer» D. 1.25 J/K
Discussion
32.

A heat engine is supplied with 800 kJ/s of heat at 600 K, and heat rejection takes place at 300 K. Which of the following results report a reversible cycle?

A. 200 kJ/s are rejected
B. 400 kJ/s are rejected
C. 100 kJ/s are rejected
D. 500 kJ/s are rejected
Answer» C. 100 kJ/s are rejected
Discussion
33.

A hot body at 1000 K transfers 2000 kJ of heat to a body at 500 K. Determine the net entropy change?

A. +4 kJ/K
B. -2 kJ/K
C. +2 kJ/K
D. -4 kJ/K
Answer» D. -4 kJ/K
Discussion
34.

Perpetual motion machine of second kind violates the

A. First law of thermodynamics
B. Kelvin-plank statements
C. Clausius statements
D. Third law of thermodynamics
Answer» C. Clausius statements
Discussion
35.

Consider the following conditions for the reversibility of a cycle:1. The P and T of the working substance must not differ appreciably, from those of the surroundings at any state in the process2. All the processes, taking place in the cycle, must be extremely slow3. The working parts of the engine must be friction-freeWhich of the above conditions are correct?

A. 1, 2 and 3
B. 1 and 2 only
C. 1 and 3 only
D. 2 and 3 only
Answer» B. 1 and 2 only
Discussion
36.

Internal combustion engine works on

A. first law of thermodynamics
B. second law of thermodynamics
C. zeroth law of thermodynamics
D. none of these
Answer» C. zeroth law of thermodynamics
Discussion
37.

For a heat engine operating on the Carnot cycle, the work output is \(\frac{1}{4}\) th of the heat transferred to the sink. The efficiency of the engine is

A. 20%
B. 33.3%
C. 40%
D. 50%
Answer» B. 33.3%
Discussion
38.

An irreversible heat engine extracts heat from a high temperature source at a rate of 100 kW and rejects heat to a sink at a rate of 50 kW. The entire work output of the heat engine is used to drive a reversible heat pump operating between a set of independent isothermal heat reservoirs at 17°C and 75°C. The rate (in kW) at which the heat pump delivers heat to its high temperature sink is

A. 50
B. 250
C. 300
D. 360
Answer» D. 360
Discussion
39.

A heat pump is a device which:

A. Convert mechanical energy into heat energy
B. Convert heat energy into mechanical energy
C. Takes heat from low temperature and delivers to high temperature with focus is on high temperature
D. Takes heat from a low temperature and delivers to high temperature with foucs is on low temperature
Answer» D. Takes heat from a low temperature and delivers to high temperature with foucs is on low temperature
Discussion
40.

If the heat rejected from the system is zero, then which of the following statements will hold TRUE?

A. When net work is equal to the heat absorbed, work efficiency is 100%.
B. Heat is exchanged from one heat reservoir only.
C. It violates Kelvin - Plank statement.
D. All options are correct
Answer» E.
Discussion
41.

If the temperature of the heat source is 1990 K and the sink is 850 K, then what is the Carnot efficiency

A. 37.2%
B. 67.4%
C. 22.7%
D. 57.3%
Answer» E.
Discussion
42.

If a closed system is undergoing an irreversible process, the entropy of the system

A. Must increase
B. Always remains constant
C. Must decrease
D. Can increase, decrease or remain constant
Answer» E.
Discussion
43.

If two Carnot engine CE1 and CE2 are connected in a series such that the heat rejected by CE1 is used as the input for the CE2 cycle with the intermediate temperature being the geometric mean of the extreme temperatures. Which of the following statement is TRUE for this efficiency of the Carnot engine?

A. ηCE1 > ηCE2
B. ηCE1 < ηCE2
C. ηCE1 = ηCE2
D. Insufficient data
Answer» D. Insufficient data
Discussion
44.

If a heat engine produces work without the consumption of energy, then what kind of machine is this?

A. Perpetual motion machine of first kind (PMM1)
B. Perpetual motion machine of second kind (PMM2)
C. Perpetual motion machine of third kind (PMM3)
D. None of these
Answer» B. Perpetual motion machine of second kind (PMM2)
Discussion
45.

A heat engine receives heat at the rate of 1500 kJ/min and gives an output of 8.2 kW, then the thermal efficiency is-

A. 47.20%
B. 41%
C. 32.80%
D. 27.90%
Answer» D. 27.90%
Discussion
46.

Consider the following statements:1. Carnot, Ericsson and Stirling cycles are ideal power cycles that are completely reversible2. Ericsson cycle is not a practical engine cycle3. Stirling cycle is the only practical power cycle among the above4. All these cycles have the same thermal efficiencyWhich of the above statements are correct?

A. 1, 2,3 and 4
B. 1, 2 and 4 only
C. 2, 3 and 4 only
D. 1, 2 and3 only
Answer» C. 2, 3 and 4 only
Discussion
47.

A reversible process _______.

A. Must pass through a continuous series of equilibrium states
B. Leaves no history of the events in surroundings
C. Must pass through the same states on the reversed path as on the forward path
D. All options are correct
Answer» E.
Discussion
48.

One reversible heat engine operates between 1600 K and T2 K and another reversible heat engine operates between T­2 K and 400 K. If both the engines have the same heat input and output, then temperature T2 is equal to

A. 800 K
B. 1100 K
C. 1200 K
D. 1400 K
Answer» B. 1100 K
Discussion
49.

An ideal gas of mass m and temperature T1 undergoes a reversible isothermal process from an initial pressure P1 to a final pressure P2. The heat loss during the process is Q. The entropy change ΔS of the gas is

A. \(mR\ln \left( {\frac{{{P_2}}}{{{P_1}}}} \right)\)
B. \(mR\ln \left( {\frac{{{P_1}}}{{{P_2}}}} \right)\)
C. \(mR\ln \left( {\frac{{{P_2}}}{{{P_1}}}} \right) - \frac{Q}{{{T_1}}}\)
D. Zero
Answer» C. \(mR\ln \left( {\frac{{{P_2}}}{{{P_1}}}} \right) - \frac{Q}{{{T_1}}}\)
Discussion
50.

A heat engine working between the source at 200°C and rejects heat at 25°C receives 5 kW of heat. Work done for this engine is equal to 0 kW. Does this satisfy the inequality of Clausius?

A. Yes
B. No
C. Cannot be determined
D. None of these
Answer» B. No
Discussion