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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151.	During a polytropic expansion 25% of heat is converted into work while temperature of gas rises by 30 K, the specific heat of gas at constant volume is
A.	10% w
B.	12 % w
C.	15% w
D.	20% w
Answer» B. 12 % w

152.	During a constant pressure expansion of a gas 33.3 % heat is converted into work while the temperature rises by 20K. The specific heat of gas at constant pressure is
A.	10% w
B.	12 % w
C.	15% w
D.	20% w
Answer» C. 15% w

153.	During an adiabatic compression when temperature increase by 100% the pressure increases by 1000%. The ratio of specific heats, ? is
A.	1.3
B.	1.35
C.	1.4
D.	1.45
Answer» C. 1.4

154.	In an constant pressure heating certain fraction of heat supplied is converted into work. If ?=1.4 this fraction is
A.	0.25
B.	0.286
C.	0.3
D.	0.327
Answer» D. 0.327

155.	The area under the curve on temperature entropy diagram represents
A.	work done during the process
B.	heat exchanged during the process
C.	change in internal energy during the process
D.	change in entropy during the process
Answer» B. heat exchanged during the process

156.	The change in entropy is zero during
A.	hyperbolic process
B.	constant pressureprocess
C.	adiabatic processes
D.	polytropic process
Answer» C. adiabatic processes

157.	Choose incorrect statement
A.	isentropic process is adiabatic
B.	adiabatic process has no heat exchange
C.	hyperbolic process is isothermal
D.	no work is done in constant pressure process
Answer» D. no work is done in constant pressure process

158.	Choose the correct statement
A.	there is no change of entropy in an adiabatic expansion
B.	entropy is an extensive property of gas derived from first law of thermodynamics
C.	the area under the curve in a temp.-entropy diagram gives the change of entropy
D.	the change of entropy during a constant pressure process is always negative
Answer» B. entropy is an extensive property of gas derived from first law of thermodynamics

159.	1.6 Kg of air is expanded at constant pressure from 100°C to 0°C resulting in entropy change of - 2.0 J/K 3.2 Kg of air is cooled at constant volume from 100°C to 0°C with a change in entropy of -3.0 J/K. The ratio Cp/ Cv is
A.	1.333
B.	1.366
C.	1.4
D.	1.43
Answer» C. 1.4

160.	Entropy at absolute zero temperature is zero for a
A.	perfect gas
B.	perfect substance
C.	perfect crystal
D.	glass
Answer» C. perfect crystal

161.	The third law of thermodynamics
A.	defines entropy
B.	provides a base from which entropy is measured
C.	defines change of entropy
D.	gives availability of heat for conversion into work
Answer» D. gives availability of heat for conversion into work

162.	Entropy is called the property of a system because
A.	it has same value at any two equilibrium states
B.	it depends upon the process path
C.	it has a unique value at each equilibrium state
D.	it does not change between two equilibriumstates
Answer» A. it has same value at any two equilibrium states

163.	Entropy of mixture of two gases after sudden mixing is
A.	greater than
B.	less than its inputtemperature
C.	same as sum of entropy ofindividual gases
D.	unpredictable
Answer» A. greater than

164.	If a substance goes though a cycle of changes returning back to original state, the change in entropy is
A.	positive
B.	negative
C.	zero
D.	positive or negative depending upon originalstate
Answer» B. negative

165.	A sequence of operations which a gas undergoes in such a way that final state is same as original state, mahe a
A.	reversible cycle
B.	irreversible cycle
C.	thermal cycle
D.	thermodynamic cycle
Answer» D. thermodynamic cycle

166.	In a reversible process
A.	heat transfer takes place over finite temperaturedifference
B.	heat transfer takes place over infinitesimaltemperature difference
C.	heat transfer takes place from surrounding to thesystem
D.	heat transfer takes place from the system tothe surrounding
Answer» C. heat transfer takes place from surrounding to thesystem

167.	Which of the following processes is very close to reversible
A.	lifting of a body above the ground
B.	compression of a gas in the cylinder against a piston
C.	flow of a fluid in a pipe
D.	motion of a boat in water
Answer» C. flow of a fluid in a pipe

168.	A perfect gas having p1= 0.1 M/mm², v1=0.18 m³, T1=20°C is compressed to 1/10 of volume in an isothermal process. The change in entropy is
A.	-141.45 j/k
B.	141.45 j/k
C.	-41446.23 j/k
D.	0
Answer» B. 141.45 j/k

169.	The enthalpy of a system
A.	i= internal energy + pv
B.	i= internal energy + pdv
C.	i= internal energy + vdp
D.	i= change in internalenergy + pv
Answer» B. i= internal energy + pdv

170.	During a polytropic expansion work obtained is 1.8 times the heat transferred. If ?=1.4, n will be
A.	1.2
B.	1.19
C.	1.178
D.	1.155
Answer» D. 1.155

171.	Which statement is wrong for throttling expansion
A.	pressure drop = 0
B.	change in enthalpy = 0
C.	work done = 0
D.	change in internalenergy = 0
Answer» C. work done = 0

172.	Which statement is wrong for adiabatic expansion
A.	h = 0
B.	w = 0
C.	ds = 0
D.	w+e = 0
Answer» D. w+e = 0

173.	Maximum amount of work that can be converted into heat in any process
A.	depends upon initial & final temperature
B.	depends upon how much work is lost in friction
C.	is 50%
D.	is 100%
Answer» B. depends upon how much work is lost in friction

174.	The universal gas constant will be equal to difference between specific heats at constant pressure & constant volume for
A.	1 kg mass of gas
B.	1 molecule of gas
C.	1 kg molecule of gas
D.	any mass of gas
Answer» C. 1 kg molecule of gas

175.	Air is compressed isothermally by performing work equal to 16 KJ upon it. The change in internal energy is
A.	- 16 kj
B.	zeroth law of thermodynamics
C.	16 kj
D.	32 kj
Answer» B. zeroth law of thermodynamics

500+ Engineering Thermodynamics Solved MCQs

During a polytropic expansion 25% of heat is converted into work while temperature of gas rises by 30 K, the specific heat of gas at constant volume is

During a constant pressure expansion of a gas 33.3 % heat is converted into work while the temperature rises by 20K. The specific heat of gas at constant pressure is

During an adiabatic compression when temperature increase by 100% the pressure increases by 1000%. The ratio of specific heats, ? is

In an constant pressure heating certain fraction of heat supplied is converted into work. If ?=1.4 this fraction is

The area under the curve on temperature entropy diagram represents

The change in entropy is zero during

Choose incorrect statement

Choose the correct statement

1.6 Kg of air is expanded at constant pressure from 100°C to 0°C resulting in entropy change of - 2.0 J/K 3.2 Kg of air is cooled at constant volume from 100°C to 0°C with a change in entropy of -3.0 J/K. The ratio Cp/ Cv is

Entropy at absolute zero temperature is zero for a

The third law of thermodynamics

Entropy is called the property of a system because

Entropy of mixture of two gases after sudden mixing is

If a substance goes though a cycle of changes returning back to original state, the change in entropy is

A sequence of operations which a gas undergoes in such a way that final state is same as original state, mahe a

In a reversible process

Which of the following processes is very close to reversible

A perfect gas having p1= 0.1 M/mm², v1=0.18 m³, T1=20°C is compressed to 1/10 of volume in an isothermal process. The change in entropy is

The enthalpy of a system

During a polytropic expansion work obtained is 1.8 times the heat transferred. If ?=1.4, n will be

Which statement is wrong for throttling expansion

Which statement is wrong for adiabatic expansion

Maximum amount of work that can be converted into heat in any process

The universal gas constant will be equal to difference between specific heats at constant pressure & constant volume for

Air is compressed isothermally by performing work equal to 16 KJ upon it. The change in internal energy is

The latent heat of vapouristation at critical point is

Choose the correct answer

With the increase in pressure

With increase in pressure

Dryness fraction of steam is defined as

Only throttling calorimeter is used for measuring

Rankine cycle efficiency of a good steam power plant may be in the range of

Rankine cycle operating on low pressure limit of p1 & high pressure limit p2

Rankine cycle comprises of

In Rankine cycle the work output from the turbine is given by

The maximum percentage gain in Regenerative feed heating cycle thermal effciency

In an unsaturated air the state of a vapour is

The efficiency of the Carnot cycle may be increased by

Most of the fossil fuel based power plants operate on

Efficiency of Rankine cycle is function of

Essential parts of a power plant operating on a Rankine cycle are

Correlate the following statements i) the volume of water into which steam is condensed in condenser is very much smaller than the volume of steam before condensation ii) the net work of a Rankine cycle is heat supplied in boiler - heat rejected to condenser - pump work

By reducing the condenser pressure in Rankine power plant

Correlate the following statements i) by reducing the condenser pressure in a Rankine cycle work output is increased ii) increased proportion of moisture in turbine is undesirable because water particles erode the blades

Turbine blade efficiency reduces in a Rankine cycle if

A Rankine cycle with reheat

The main advantage of a Reheat Rankine cycle is

A Reheat Rankine cycle

Choose the wrong statement

Examine follwing two statements & choosethe correct relationship i) for a steam power plant Rankine cycle is preferred over Carnot cycle ii) a pump which will handle the mixture of vapour & liquid is difficult to construct

Correlate the following statements
i) the volume of water into which steam is condensed in condenser is very much smaller than the volume of steam before condensation
ii) the net work of a Rankine cycle is heat supplied in boiler - heat rejected to condenser - pump work

Correlate the following statements
i) by reducing the condenser pressure in a Rankine cycle work output is increased
ii) increased proportion of moisture in turbine is undesirable because water particles erode the blades

Examine follwing two statements & choosethe correct relationship
i) for a steam power plant Rankine cycle is preferred over Carnot cycle
ii) a pump which will handle the mixture of vapour & liquid is difficult to construct

176.	The latent heat of vapouristation at critical point is
A.	less than zero
B.	greater than zero
C.	equal to zero
D.	none of the above
Answer» C. equal to zero

177.	Choose the correct answer
A.	critical point involves equilibrium of solid & vapour phases
B.	critical point involves equilibrium of solid & liquid phases
C.	critical point involves equilibrium of solid, liquid & vapour phases
D.	triple point involves equilibrium of solid, liquid & vapour phases
Answer» D. triple point involves equilibrium of solid, liquid & vapour phases

178.	With the increase in pressure
A.	boiling point of water increases & enthalpy of evaporation increases
B.	boiling point of water increases & enthalpy of evaporation decreases
C.	boiling point of water decreases & enthalpy of evaporation increases
Answer» B. boiling point of water increases & enthalpy of evaporation decreases

179.	With increase in pressure
A.	enthalpy of dry saturated steam increases
B.	enthalpy of dry saturated steam decreases
C.	enthalpy of dry saturated steam remains same
D.	enthalpy of dry saturated steam first increases & thendecreases
Answer» B. enthalpy of dry saturated steam decreases

180.	Dryness fraction of steam is defined as
A.	mass of water vapour in suspension/(mass of water vapour in suspension+mass of dry steam)
B.	mass of dry steam/mass of water vapour in suspension
C.	mass of dry steam/(mass of dry steam+mass of water vapour in suspension)
D.	mass of water vapour in suspension/mass of dry steam
Answer» C. mass of dry steam/(mass of dry steam+mass of water vapour in suspension)

181.	Only throttling calorimeter is used for measuring
A.	very low dryness fraction upto 0.7
B.	very high dryness fraction upto 0.98
C.	dryness fraction of only low pressure steam
D.	dryness fraction ofonly high pressure steam
Answer» B. very high dryness fraction upto 0.98

182.	Rankine cycle efficiency of a good steam power plant may be in the range of
A.	15 to 20%
B.	35 to 45%
C.	70 to 80%
D.	90 to 95%
Answer» B. 35 to 45%

183.	Rankine cycle operating on low pressure limit of p1 & high pressure limit p2
A.	has higher thermal efficiency than the carnot cycle operating between same pressure limits
B.	has lower thermal efficiency than carnot cycle operating between same pressurelimits
C.	has same thermal efficiency than carnot cycle operating between same pressure limits
D.	may be more or less depending upon the magnitudes of p1 & p2
Answer» A. has higher thermal efficiency than the carnot cycle operating between same pressure limits

184.	Rankine cycle comprises of
A.	two isetropic processes & two constant volume processes
B.	two isentropic processes & two constant pressureprocesses
C.	two isothermal processes & two constant pressureprocesses
D.	none of the above
Answer» B. two isentropic processes & two constant pressureprocesses

185.	In Rankine cycle the work output from the turbine is given by
A.	change of internal energy between inlet & outlet
B.	change of enthalpy between inlet & outlet
C.	change of entropy between inlet & outlet
D.	change of temperature between inlet & outlet
Answer» B. change of enthalpy between inlet & outlet