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.

101.

The amount of heat absorbed by a system at lower temperature is

A. coeff. of performance
B. efficiency
C. work supplied
D. refrigerating effect
Answer» C. work supplied
102.

Tds equation is

A. a) tds=cvdt + t
B. ..
Answer» A. a) tds=cvdt + t
103.

In an ideal gas the partial pressure of a component is

A. inversely proportional to the square of the molefraction
B. directly proportional to the mole fraction
C. inversely proportional to the mole fraction
D. equal to the mole fraction
Answer» B. directly proportional to the mole fraction
104.

The value of the univesal gas constant is

A. 0.314 j/kg k
B. 83.14 kj/kg k
C. 848 kj/kg k
D. 8.314 kj/kg k
Answer» D. 8.314 kj/kg k
105.

Choose the correct answer

A. a perfect gas does not obey the law pv=rt
B. a perfect gas obeys the law pv=rt & has constant specific heat
C. a perfect gas obeys the law pv=rt but have variable specific heat capacities
D. all of the above
Answer» B. a perfect gas obeys the law pv=rt & has constant specific heat
106.

Boyle's law states that, when tempearture is constant, the volume of a given mass of a perfect gas

A. varies directly as the absolute pressure
B. varies inversely as the absolute pressure
C. varies as square of the absolute pressue
D. does not vary with the absolute pressure
Answer» B. varies inversely as the absolute pressure
107.

Charle's law states that if any gas is heated at constant pressure, its volume

A. changes directly as it absolute temperature
B. changes inversely as its absolute temperature
C. changes as square of the absolute temperature
D. does not change with absolute temperature
Answer» A. changes directly as it absolute temperature
108.

The equation of state of an ideal gas is a relationship between the variables:

A. pressure & volume
B. pressure & temperature
C. pressure, volume & temperature
D. none of the above
Answer» C. pressure, volume & temperature
109.

Joule's law states that the specific internal energy of a gas depends only on

A. the pressure of the gas
B. the volume of the gas
C. the temperature of the gas
D. none of the above
Answer» C. the temperature of the gas
110.

………. Law states that equal volume of all gases, at the same temperature & pressure, contains equal number of molecules

A. boyle's
B. gay-lussac
C. avogadro
D. charle's
Answer» C. avogadro
111.

The change of entropy is considered to be ……… when heat is absorbed by the gas

A. positive
B. negative
C. zero
D. none of the above
Answer» A. positive
112.

………. Is one in which neither any heat enters nor leaves the system

A. isochoric process
B. isobaric process
C. isentropic process
D. isothermal process
Answer» C. isentropic process
113.

Entropy of the universe

A. tends to zero
B. tends to a minimum
C. tends to a maximum
D. none of the above
Answer» C. tends to a maximum
114.

A gas can never be liquid

A. above criticaltemperature
B. when it is diatomic
C. when it is impure
D. above roomtemperature
Answer» A. above criticaltemperature
115.

Which of the following remains constant during an adiabatic expansion

A. entropy
B. temperature
C. internal energy
D. none of the above
Answer» A. entropy
116.

In which of the following processes the change in internal energy of a gas is equal to the work done

A. adiabatic process
B. isothermal process
C. constant volume process
D. constant pressure process
Answer» A. adiabatic process
117.

The specific heat of a gas is a function of

A. temperature only
B. temperature & pressure
C. temperature & entropy
D. temperature, pressure& entropy
Answer» A. temperature only
118.

In a Carnot cycle which of the following processez must be carried out at extremely slow speed?

A. isothermal compression
B. adiabatic expansion
C. adiabatic compression
D. none of the above
Answer» A. isothermal compression
119.

In the case of real gases, cp will be equal to cv

A. at absolute zero
B. at triple point
C. at critical temperature
D. above criticaltempeature
Answer» A. at absolute zero
120.

The physical properties of a perfect gas are controlled by which of the following variables?

A. volume
B. temperature
C. pressure
D. all of the above
Answer» D. all of the above
121.

Universal gas constant is defined as equal to the product of the molecular weight of the gas &

A. gas constant
B. specific heat at constant volume
C. specific heat a constant pressure
D. ratio of two specific heats
Answer» A. gas constant
122.

All engineering process, strictly speaking are

A. reversible cycle
B. irreversible
C. quasti-static
D. thermodynamically inequillibrium
Answer» D. thermodynamically inequillibrium
123.

Isothermal, isobaric, isochoric & adiabatic processes, under ideal conditions, are …. Processes

A. thermodynamic
B. stable
C. dynamic
D. quasi-static
Answer» D. quasi-static
124.

Change of entropy depends upon which of the following?

A. change of heat
B. change of specific heats
C. change of pressure &volume
D. none of the above
Answer» A. change of heat
125.

In a reversible adiabatic process head added is equal to

A. zero
B. positive value
Answer» A. zero
126.

During a throttling process

A. exchange of heat doesnot take place
B. expandingsteam does nowork
C. internal energy of steamdoes not change
D. all of the above
Answer» D. all of the above
127.

Under which of the following conditions all gases behave ideally?

A. high pressure conditions
B. law pressure conditions
C. vaccum conditions
D. all of the aboveconditions
Answer» B. law pressure conditions
128.

……….. Is the unit of entropy

A. j/kg
B. j/kg k
C. j/k
D. j/kgs
Answer» B. j/kg k
129.

Internal energy & enthalpy of an ideal gas are functions of

A. pressure only
B. temperature only
C. specific volume only
D. temperature & pressure
Answer» B. temperature only
130.

When two gases suddenly mix up with each other then resultant entropy of the system will

A. remain unaltered
B. decrease
C. increase
D. becomes zero
Answer» C. increase
131.

On which of the following factors does air standard efficiency of a diesel cycle depend?

A. adiabatic compression ratio
B. ratio of specific heats
C. cut-off ratio
D. all of the above
Answer» D. all of the above
132.

Regarding enthalpy which of the following statements is incorrect?

A. it is the function of specific heat at constantvolume
B. it is the extensive property of the system
C. it is the sum of internal energy & the pressurevolume product
D. it is the same as heat transfer during constantpressure process
Answer» A. it is the function of specific heat at constantvolume
133.

Which of the following processes is reversible process?

A. throttling
B. adiabatic
C. isothermal
D. none of the above
Answer» A. throttling
134.

Which of the following processes are reversible processes?

A. isothermal & adiabatic
B. constant volume &constant pressure
C. hyperbolic & pv?= constant
D. none of the above
Answer» A. isothermal & adiabatic
135.

For ……. The internal energy & enthalpy are the functions of temperature only

A. perfect gas
B. water in pipes surrounded by steam
C. saturated steam
D. superheated steam
Answer» A. perfect gas
136.

The index of compression n tends to reach ?(ratio of specific heats)

A. when process is isothermal
B. when process is isentropic
C. when process is isentropic & specific heat does not change with temperature
D. when flow is uniform & steady
Answer» C. when process is isentropic & specific heat does not change with temperature
137.

In the reversible polytropic process the value of exponent n varies between

A. 0.2 to 1
B. 1.0 to 1.2
C. 1.2 to 1.4
D. 1.4 to 2.0
Answer» C. 1.2 to 1.4
138.

An ideal gas as compared to a real gas at very high pressure occupies

A. same volume
B. less volume
C. more volume
D. all of the above
Answer» C. more volume
139.

Adiabatic & isothermal processes are identical at

A. absolute zerotemperature
B. below 0°c temperature
C. saturation temperature
D. critical temperature
Answer» A. absolute zerotemperature
140.

In polytropic process pv?=C the value of exponent n=±? is indicative of

A. isobaric process
B. isentropic process
C. isochoric process
D. throttling process
Answer» C. isochoric process
141.

Entropy in statistical thermodynamics is defined as

A. a universal property
B. reversible heat transfer
C. degree of randomness
D. measure of reversibilityof a system
Answer» C. degree of randomness
142.

A mixture of gases expands from 0.03 m³ to 0.06 m³ at a constant pressure of 1 Mpa & absorbs 84 kJ of heat during the process. The change in internal energy of the mixture is

A. 30 kj
B. 54 kj
C. 84 kj
D. 114 kj
Answer» B. 54 kj
143.

Increase in entropy of a system represents

A. increase in availability ofenergy
B. increase in temperature
C. decrease in pressure
D. degradation of energy
Answer» D. degradation of energy
144.

Which one of the following pairs best expresses a relationship similar to that expressed in the pair 'pressure-volume' for a thermodynamic system undergoing a process?

A. enthalpy-entropy
B. pressure-enthalpy
C. pressure-temperature
D. temperature-entropy
Answer» D. temperature-entropy
145.

Variations of pressure & volume at constant temperature are correlated through

A. charle's law
B. boyle's law
C. gas law
D. gay lussac's law
Answer» B. boyle's law
146.

The relationship between pressure & volume is expressed as pv?=const. Select wrong statement

A. expansion with n=0 is a constant pressure process
B. expansion with n=? is an adiabatic process
C. expansion with n=? is not possible
D. expansion at constant temperature has n=1
Answer» C. expansion with n=? is not possible
147.

A gas expands from initial condition of (p1, v1, T1) to final condition (p2, v1, T2), then according to Charle's law:

A. p1t1=p2t2
B. p1p2 = t1t2
C. p1+ t2 = p2 + t1
D. p1t2 = p2t1
Answer» D. p1t2 = p2t1
148.

Air expands from initial condition of p1, v1 to final condition of 1/2 p1, 2v1. Choose the correct statement

A. no work is performed during expansion
B. expansion is isothermal
C. expansion is polytropic with n= 1.2
D. expansion is adiabatic
Answer» C. expansion is polytropic with n= 1.2
149.

Air with initial condition of p1, v1 expands to final condition of p1/2, 3v1. The process is

A. hyperbolic
B. adiabatic
C. polytropic with n > 1
D. polytropic with n < 1
Answer» A. hyperbolic
150.

The internal energy of a perfect gas is a function of

A. pressure change &temperature
B. temperature change &specific heat
C. pressure & work supplied
D. temperature
Answer» D. temperature
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
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
186.

The maximum percentage gain in Regenerative feed heating cycle thermal effciency

A. increases with number of feed heaters increasing
B. decreases with number of feed heaters increasing
C. remains same unaffected by number of feed heaters
D. none of the above
Answer» A. increases with number of feed heaters increasing
187.

In an unsaturated air the state of a vapour is

A. wet
B. superheated
C. saturated
D. unsaturated
Answer» B. superheated
188.

The efficiency of the Carnot cycle may be increased by

A. decreasing the lowest temperature
B. increasing the lowest temperature
C. increasing the highest temperature
D. both a & c
Answer» D. both a & c
189.

Most of the fossil fuel based power plants operate on

A. rankine cycle
B. brayton cycle
C. carnot cycle
D. either rankine or brayton cycle
Answer» D. either rankine or brayton cycle
190.

Efficiency of Rankine cycle is function of

A. highest temperature of cycle
B. lowest temperature of cycle
C. both highest & lowest temperature of the cycle
D. none of the above
Answer» C. both highest & lowest temperature of the cycle
191.

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

A. engine or turbine
B. engine or turbine & conderser
C. gine or turbine, condenser, pump &boiler
D. engine or turbine & boiler
Answer» C. gine or turbine, condenser, pump &boiler
192.

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

A. both i) & ii) are correct, i) is the correct reason for ii)
B. i) & ii) are correct, ii) is the correct interpretation if i)
C. both i) & ii) are not correct
D. both i) & ii) are independently correct
Answer» D. both i) & ii) are independently correct
193.

By reducing the condenser pressure in Rankine power plant

A. heat supplied increases & work of cycle decreases
B. work of cycle & moisture content of steam in l.p side ofturbine increase
C. heat supplied & efficiency of cycle increase
D. work of cycle increases but heat supplied decreases
Answer» B. work of cycle & moisture content of steam in l.p side ofturbine increase
194.

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

A. both i) & ii) are independently true
B. both i) & ii) are not true
C. i) is true but ii) is not
D. ii) is true but i) is not
Answer» A. both i) & ii) are independently true
195.

Turbine blade efficiency reduces in a Rankine cycle if

A. heat supply in boiler increases
B. heat supply in boiler decreases
C. condenser pressure decreases
D. condenser pressure increases
Answer» C. condenser pressure decreases
196.

A Rankine cycle with reheat

A. increases heat supply but reduces work
B. increases efficiency but reduces work
C. increases moisture content in l.p side of turbine but increases work
D. increases efficiency but reduces moisture content in l.p side of turbine
Answer» D. increases efficiency but reduces moisture content in l.p side of turbine
197.

The main advantage of a Reheat Rankine cycle is

A. reduced moisture content in l.p side of turbine
B. increased efficiency
C. increased work of turbine
D. reduced load on condenser
Answer» A. reduced moisture content in l.p side of turbine
198.

A Reheat Rankine cycle

A. reduces total heat produced in boiler
B. increases total heat produced in boiler
C. increases volume of steam produced in boiler
D. reduces volume of steam produced inboiler
Answer» B. increases total heat produced in boiler
199.

Choose the wrong statement

A. volume of steam passing through h.p & l.p sides of the turbine is same in simple rankine cycle
B. volume of steam passing through l.p side of turbine & condenser is same in regenerative rankine cycle
C. volume of steam passing through h.p side of the turbine & condenser is same in regenerative rankinecycle
D. volume of steam passing through h.p side of the turbine & condenser is same in reheat rankine cycle
Answer» C. volume of steam passing through h.p side of the turbine & condenser is same in regenerative rankinecycle
200.

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

A. both i) ii) are correct & i) is the consequence of ii)
B. both i) & ii) are independently correct
C. i) is correct but ii) is not
D. ii) is correct but i) is not
Answer» A. both i) ii) are correct & i) is the consequence of ii)
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