500+ Engineering Thermodynamics Solved MCQs

Engineering thermodynamics is a branch of engineering that deals with the study of energy, heat, and their relationship to work and the transfer of energy from one place to another.

It is a fundamental subject that forms the basis of many other branches of engineering, including mechanical, chemical, and electrical engineering. The principles of thermodynamics are used to design engines, power plants, refrigeration systems, and a wide variety of other devices and systems that are essential to modern society. Some of the key concepts in engineering thermodynamics include the laws of thermodynamics, entropy, and the concept of equilibrium.

These multiple-choice questions (MCQs) are designed to enhance your knowledge and understanding in the following areas: Mechanical Engineering .

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51.	The main cause of the irreversibility is
A.	mechanical & fluid friction
B.	unrestricted expansion
C.	heat transfer with a finite temperature difference
D.	all of the above
Answer» D. all of the above

52.	An isentropic process is always
A.	irreversible & adiabatic
B.	reversible & isothermal
C.	frictionless & irreversible
D.	reversible & adiabatic
Answer» D. reversible & adiabatic

53.	In the polytropic process equation pvⁿ = constant, if n is infinitely large, the process is termed as
A.	constant volume
B.	constant pressure
C.	constant temperature
D.	diabatic
Answer» A. constant volume

54.	Second law of thermodynamics defines
A.	heat
B.	work
C.	enthalpy
D.	entropy
Answer» D. entropy

55.	For a reversible adiabatic process, the change in entropy is
A.	zero
B.	minimum
C.	maximum
D.	infinite
Answer» A. zero

56.	For any reversible process, the change in entropy of the system & surroundings is
A.	zero
B.	unity
C.	negative
D.	positive
Answer» A. zero

57.	For any irreversible process the net entropy change is
A.	zero
B.	positive
C.	negative
D.	infinite
Answer» B. positive

58.	The processes of a Carnot cycle are
A.	two adiabatic & two constant volume
B.	one constant volume &one constant pressure & two isentropies
C.	two adiabatics & two isothermals
D.	two isothermals & two isentropies
Answer» D. two isothermals & two isentropies

59.	Isentropic flow is
A.	irreversible adiabatic flow
B.	ideal fluid flow
C.	reversible adiabatic flow
D.	frictionless reversible flo
Answer» C. reversible adiabatic flow

60.	In a carnot engine, when the working substance gives heat to the sink
A.	the temperature of the sink increases
B.	the temperature of the sink remains the same
C.	the temperature of the source decreses
D.	the temperature of the source decrease
Answer» B. the temperature of the sink remains the same

61.	If the temperature of the source is increased, the efficiency of the Carnot engine
A.	decrease
B.	increase
C.	does not change
D.	will be equal to the efficiency of a practicalengine
Answer» B. increase

64.	Kelvin-Plank's law deals with
A.	conservation of energy
B.	conservation of heat
C.	conservation of mass
D.	conversion of heat intowork
Answer» D. conversion of heat intowork

65.	Which of the following statements is correct according to Clausius statement of second law of thermodynamics?
A.	it is impossible to transfer heat from a body at a lower temperature to a body at a higher temperature
B.	it is impossible to transfer heat from a body at a lower temperature to a body at a higher temperature, without the aid of an external source
C.	it is possible to transfer heat from a body at a lower temperature to a body at a higher temperature by using refrigeration cycle
D.	none of the above
Answer» B. it is impossible to transfer heat from a body at a lower temperature to a body at a higher temperature, without the aid of an external source

71.	The efficiency of the Carnot cycle may be increased by
A.	increasing the highesttemperature
B.	decreasing the highesttemperature
C.	increasing the lowesttemperature
D.	decreasing the lowesttemperature
Answer» D. decreasing the lowesttemperature

73.	The reversible engines are
A.	least efficient
B.	most efficient
C.	having same efficiency asirreversible engines
D.	none of the above
Answer» B. most efficient

62.	The efficiency of an ideal Carnot engine depends on
A.	working substance
B.	on the temperature of the source only
C.	on the temperature of the sink only
D.	on the temperatures of both the source & the sink
Answer» D. on the temperatures of both the source & the sink

63.	In a reversible cycle, the entropy of the system
A.	increases
B.	decreases
C.	does not change
D.	first increases & thendecreases
Answer» C. does not change

66.	The property of a working substance which increases or decreases as the heat is supplied or removed in a reversible manner is known as
A.	enthalpy
B.	internal energy
C.	entropy
D.	external energy
Answer» C. entropy

67.	The entropy may be expressed as a function of
A.	pressure & temperature
B.	temperature & volume
C.	heat & work
D.	all of the above
Answer» A. pressure & temperature

68.	The change of entropy when heat is absorbed by the gas is
A.	positive
B.	negative
C.	positive or negative
D.	all of the above
Answer» A. positive

69.	Which of the following statements is correct?
A.	the increase in entropy is obtained from a given quantity of heat at a low temperature
B.	the change in entropy may be regarded as a measure of the rate of the availability of heat fortransformation into work
C.	the entropy represents the maximum amount of work obtainable per degree drop in temperature
D.	all of the above
Answer» D. all of the above

70.	In an irreversible process, there is a
A.	loss of heat
B.	no loss of work
C.	gain of heat
D.	no gain of heat
Answer» A. loss of heat

72.	Which of the following is the correct statement?
A.	all the reversible engines have the same efficiency
B.	all the reversible & irreversible engines have the same efficiency
C.	irreversible engines have maximum efficiency
D.	all engines are designed as reversible in order to obtain maximum efficiency
Answer» A. all the reversible engines have the same efficiency

74.	Gases could have an infinite number of specific heats but only ……. Specific heats are defined
A.	one
B.	two
C.	three
D.	four
Answer» B. two

75.	The area under the T-s (temperature - entropy) curve of any thermodynamic process represents
A.	heat rejected only
B.	heat absorbed only
C.	work done during the process
D.	heat absorbed or rejected
Answer» D. heat absorbed or rejected

500+ Engineering Thermodynamics Solved MCQs

The main cause of the irreversibility is

An isentropic process is always

In the polytropic process equation pvⁿ = constant, if n is infinitely large, the process is termed as

Second law of thermodynamics defines

For a reversible adiabatic process, the change in entropy is

For any reversible process, the change in entropy of the system & surroundings is

For any irreversible process the net entropy change is

The processes of a Carnot cycle are

Isentropic flow is

In a carnot engine, when the working substance gives heat to the sink

If the temperature of the source is increased, the efficiency of the Carnot engine

The efficiency of an ideal Carnot engine depends on

In a reversible cycle, the entropy of the system

Kelvin-Plank's law deals with

Which of the following statements is correct according to Clausius statement of second law of thermodynamics?

The property of a working substance which increases or decreases as the heat is supplied or removed in a reversible manner is known as

The entropy may be expressed as a function of

The change of entropy when heat is absorbed by the gas is

Which of the following statements is correct?

In an irreversible process, there is a

The efficiency of the Carnot cycle may be increased by

Which of the following is the correct statement?

The reversible engines are

Gases could have an infinite number of specific heats but only ……. Specific heats are defined

The area under the T-s (temperature - entropy) curve of any thermodynamic process represents

Second law of thermodynamics defines

For storing a gas which one of the following types of compression will be ideal

A process which can be stopped at any stage & reversed so that the system & the surroundings are exactly restored to their initial states is known as

Which of the following is a reversible process?

Leaking of air from a punctured tube is an example of

To convert volumetric analysis to gravimetric analysis, the relative volume of each constituent of the flue gases is

a heat engine receives heat at the rate of 1500 kJ/min.& gives an output of 8.2 kW. Its thermal efficiency is equal to

An inventor claims that a new heat cycle will develop 0.4 kW for a heat addition of 32.5 kJ/mm. The temperature of heat source is 1990 K & that of sink is 850K. Is his claim true?

Consider the following statements: The definition of 1. temperature is due to zeroth law of thermodynamics 2. entropy is due to first law of thermodynamics 3. internal energy is due to second law of thermodynamics 4. reversibility is due to Kelvin-Planck's ststement of these statements

A heat engine is supplied with 250 kJ/s of heat at a constant fixed temperature of 227°C. The heat is rejected at 27°C. The cycle is reversible, if the amount of heat rejected is

A Carnot engine receiving heat at 400K has an efficiency of 25%. The C.O.P. of a Carnot refrigerator working between the same temperature limits is

If a heat enine gives an output of 3 kW when the input is 10,000 J/s, then the thermal efficiency of the engine will be

The fundamental unit of enthalpy is

In a cyclic heat engine operating between a source temperature of 600°C & a sink temperature of 20°C, the least rate of heat rejection per kW net output of the engine is

In a reversible cycle, the source temperature is 227°C & the sink temperature is 27°C. The maximum available work for a heat input of 100 kJ will be

A heat engine using lake water at 12° C as source & the surrounding atmosphere at 2°C as sink executes 1080 cycles per min. If the amount of heat drawn per cycle is 57J, then the output of the engine will be

One reversible heat engine operates between 1600 K & T₂ K & another reversible heat engine operates between T₂ K & 400 K. If both the engines have the temperature T₂ must be equal to

An engine receives 15152 J/s of heat & produces 5 KW of power. The efficiency of the engine is

Choose the correct statement

The second law of thermodynamics defines

Which law of thermodynamics defines entropy

Which of the following processes is essentially irreversible

A thermodynamic cycle operates between 400 K. & 290 K. 500 MJ/s of heat is added to the working substance. The power generated is

A reversible engine performing as engine has efficiency of 62.5%. If it is reversed to work as refrigerator its COP will be

A reversible engine performing as refrigerator has COP=33%. If the same machine operates as engine, its efficiency will be

Consider the following statements: The definition of
1. temperature is due to zeroth law of thermodynamics
2. entropy is due to first law of thermodynamics
3. internal energy is due to second law of thermodynamics
4. reversibility is due to Kelvin-Planck's ststement of these statements

77.	For storing a gas which one of the following types of compression will be ideal
A.	constant volume
B.	polytropic
C.	adiabatic
D.	isothermal
Answer» D. isothermal

78.	A process which can be stopped at any stage & reversed so that the system & the surroundings are exactly restored to their initial states is known as
A.	thermodynamic process
B.	irreversible process
C.	reversible process
D.	isothermal process
Answer» C. reversible process

79.	Which of the following is a reversible process?
A.	throttling
B.	combustion
C.	free expansion
D.	extension &compression of a spring
Answer» D. extension &compression of a spring

80.	Leaking of air from a punctured tube is an example of
A.	isothermal expansion
B.	adiabatic expansion
C.	throttling
D.	constant pressureexpansion
Answer» C. throttling

81.	To convert volumetric analysis to gravimetric analysis, the relative volume of each constituent of the flue gases is
A.	divided by its specific weight
B.	multiplied by its density
C.	multiplied by its molecular weight
D.	divided by its molecular weight
Answer» C. multiplied by its molecular weight

82.	a heat engine receives heat at the rate of 1500 kJ/min.& gives an output of 8.2 kW. Its thermal efficiency is equal to
A.	20.5 %
B.	30.2%
C.	32.8%
D.	44.6%
Answer» C. 32.8%

83.	An inventor claims that a new heat cycle will develop 0.4 kW for a heat addition of 32.5 kJ/mm. The temperature of heat source is 1990 K & that of sink is 850K. Is his claim true?
A.	true
B.	false
C.	either of the above
D.	unpredictable
Answer» B. false

84.	Consider the following statements: The definition of 1. temperature is due to zeroth law of thermodynamics 2. entropy is due to first law of thermodynamics 3. internal energy is due to second law of thermodynamics 4. reversibility is due to Kelvin-Planck's ststement of these statements
A.	1,2 & 3 are correct
B.	1,3 & 4 are correct
C.	1 alone is correct
D.	2 alone is correct
Answer» C. 1 alone is correct

85.	A heat engine is supplied with 250 kJ/s of heat at a constant fixed temperature of 227°C. The heat is rejected at 27°C. The cycle is reversible, if the amount of heat rejected is
A.	273 kj/s
B.	200 kj/s
C.	180 kj/s
D.	150 kj/s
Answer» D. 150 kj/s

86.	A Carnot engine receiving heat at 400K has an efficiency of 25%. The C.O.P. of a Carnot refrigerator working between the same temperature limits is
A.	1
B.	2
C.	3
D.	4
Answer» C. 3