# 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.

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1.

## A definite area or space where some thermodynamic process takes place is known as

A. thermodynamic system
B. thermodynamic cycle
C. thermodynamic process
D. thermodynamic law
2.

## An open system is one in which

A. heat & work cross the boundary of the system, but the mass of the working substance does not
B. mass of working substance crosses the boundary of the system but the heat & work do not
C. both the heat & work as well as mass of the working substance cross the boundary of the system
D. neither the heat & work nor the mass of the working substances cross the boundary of the system
Answer» C. both the heat & work as well as mass of the working substance cross the boundary of the system
3.

## An isolated system

A. is a specified region where transfer of energy and/or mass take place
B. is a region of constant mass & only energy is allowed to cross the boundaries
C. cannot transfer either energy or mass to or from the surroundings
D. is one in which mass within the system is not necessarily constant
Answer» C. cannot transfer either energy or mass to or from the surroundings
4.

A. volume
B. temperature
C. mass
D. energy
5.

A. pressure
B. volume
C. temperature
D. density
6.

## When two bodies are in thermal equilibrium with a third body they are also in thermal equilibrium with each other. This statement is called

A. zeroth law of thermodynamics
B. first law of thermodynamics
C. second law of thermodynamics
D. kelvin planck's law
Answer» A. zeroth law of thermodynamics
7.

## The temperature at which the volume of a gas becomes zero is called

A. absolute scale of temperature
B. absolute zero temperature
C. absolute temperature
D. none of the above
8.

A. 100 n/m??
B. 1000 n/m??
C. 1??10⁴ n/m??
D. 1??10⁵ n/m??
9.

## The absolute zero pressure will be

A. when molecular momentum of the systembecomes zero
B. at sea level
C. at the temperature of -273 k
D. under vaccum conditions
Answer» A. when molecular momentum of the systembecomes zero
10.

A. -273°c
B. 273°c
C. 237°c
D. -373°c
11.

## Which of the following is correct?

A. absolute pressure= guage pressure+ atmosphericpressure
B. guage pressure= absolute pressure + atmosphericpressure
C. atmospheric pressure= absolute pressure+ guagepressure
D. absolute pressure= guage pressure-atmospheric pressure
Answer» A. absolute pressure= guage pressure+ atmosphericpressure
12.

## The unit of energy in SI units is

A. joule (j)
B. joule metre (jm)
C. watt (w)
D. joule/metre (j/m)
13.

A. 1 nm/s
B. 1n/min
C. 10 n/s
D. 100 nm/s
14.

A. 1 nm
B. knm
C. 10 nm/s
D. 10 knm/s
15.

## A series of operations, which take place in a certain order & restore the initial condition is known as

A. reversible cycle
B. irreversible cycle
C. thermodynamic cycle
D. none of the above
16.

## The condition for the reversibility of a cycle is

A. the pressure & temperature of the working substance must not differ, appreciably, from those of
B. all the processes, taking place in the cycle of operation, must be extremely slow
C. the working parts of the engine must be friction free
D. all of the above
Answer» D. all of the above
17.

## According to kinetic theory of heat

A. temperature should rise during boiling
B. temperature should fall during freezing
C. at low temperature all bodies are in solid state
D. at absolute zero there is absolutely no vibration ofmolecules
Answer» D. at absolute zero there is absolutely no vibration ofmolecules
18.

## A system comprising a single phase is called a

A. closed system
B. open system
C. isolated system
D. homogeneous system
19.

C. uniform flow
D. closed flow
20.

## A control volume refers to

A. a fixed region in space
B. a specified mass
C. an isolated system
D. a reversible process only
Answer» A. a fixed region in space
21.

## Internal energy of a perfect gas depends on

A. temperature, specificheats & pressure
B. temperature, specificheats & enthalpy
C. temperature, specific heats& entropy
D. temperature only
22.

## Steady flow process requires that

A. conditions do not change with time at any point
B. conditions are the same at adjacent points at anyinstant
C. conditions change steadily with the time
D. is constant
Answer» A. conditions do not change with time at any point
23.

## The first law of thermodynamics for steady flow

A. accounts for all energy entering & leaving a controlvolume
B. is an energy balance for a specified mass of fluid
C. is an expression of the conservation of linearmomentum
D. is primarily concerned with heat transfer
Answer» A. accounts for all energy entering & leaving a controlvolume
24.

## Which of the following is not a property of the system

A. temperature
B. pressure
C. specific volume
D. heat
25.

## The process or systems that do not involve heat are called

A. isothermal processes
B. equilibrium processes
26.

## Which one of the following statements is correct?

A. pressure is an extensiveproperty
B. density is an intensiveproperty
C. density is an extensiveproperty
D. temperature is anextensive property
Answer» B. density is an intensiveproperty
27.

A. mass
B. momentum
C. energy
D. heat
28.

## Which one of the following processes or systems does not involve heat

B. isothermal processes
D. thermal processes
29.

## Thermodynamic equillibrium is completely defined by the specification of

A. generalised displacements
B. internal energy
C. enthalpy
D. all of the above
Answer» D. all of the above
30.

## ………. Is not a property of the system

A. pressure
B. temperature
C. heat
D. specific volume
31.

## In which of the following processes the external work done is not zero?

A. throttling
B. free expansion
C. constant volume process
D. constant pressureprocess
32.

## The extension & compression of a helical spring is an example of

A. irreversible process
B. reversible process
C. isothermal process
33.

## In all irrevesible processes, the entropy of the system

A. remains unaltered
B. reduces to zero
C. increases
D. none of the above
34.

## Temperature of a gas is produced due to which of the following?

A. attraction of molecules
B. repulsion of molecules
C. kinetic energy of molecules
D. all of the above
Answer» C. kinetic energy of molecules
35.

## The same volume of all gases at same temperatureand pressure would represent their

A. specific gravity
B. densities
C. specific weights
D. molecular weights
36.

## First law of thermodynamics gives relationship between which of the following?

A. heat & internal energy
B. heat & work
C. heat, work & properties of the system
D. various thermodynamics processes
Answer» C. heat, work & properties of the system
37.

## The temperature in a process in which work is done by expanding a gas under adiabatic condition will

A. decrease
B. increase
C. first decrease & then increase
D. remain unaltered
38.

## On which of the following laws measurement of temperature is based?

A. joule's law
B. zeroth law of thermodynamics
C. first law of thermodynamics
D. second law of thermodynamics
Answer» B. zeroth law of thermodynamics
39.

## The perpetual motion of the first kind is represented by which of the following?

A. a machine that continuously creates itsown energy
B. an engine with 100 percent efficiency
C. a fully reversible engine
D. none of the above
Answer» A. a machine that continuously creates itsown energy
40.

## Which of the following statements regarding a perpetual motion machine is correct?

A. it is an in efficient machine
B. it is non-thermodynamic machine
C. it is thermodynamic machine
D. it is hypothetic machine whose operation would violate the laws of thermodynamics
Answer» D. it is hypothetic machine whose operation would violate the laws of thermodynamics
41.

## Which of the following statements, regarding a property of system, is correct?

A. it is path function
B. it is a point function
C. it is always of intensive type
D. none of the above
Answer» B. it is a point function
42.

## ……….. Is an intensive property

A. specific volume
B. total volume
C. total mass
D. total energy of a system
43.

## A system is said to be in thermodynamic equilibrium if it is in

A. chemical equilibrium
B. thermal equilibrium
C. mechanical equilibrium
D. all of the above
Answer» D. all of the above
44.

A. zeroth
B. first
C. second
D. third
45.

## As differentials, heat & work would be described mathematically as

A. exact
B. inexact
C. point function
D. discontinuity
46.

## Which of the following is an open thermodynamic system?

A. pressure cooker
B. manual ice cream freezer
C. centrifugal pump
D. none of the above
47.

## ……… is a non-quasistatic process

A. free expansion of gas
B. expansion of gas in a cylinder under constantpressure
C. rapid leakage of air from a bicycle tyre
D. gradual compression of gas inside a piston-cylinderarrangement
Answer» A. free expansion of gas
48.

## Choose the correct statement

A. pressure, temp. &entropy are extensive properties
B. pressure, temp. &entropy are intensive properties
C. pressure, volume & temp. are extensive properties
D. volume & entropy are extensive properties
Answer» D. volume & entropy are extensive properties
49.

## The first law of thermodynamics defines

A. entropy
B. internal energy
C. work
D. heat
50.

## A process becomes irreversible due to

A. work performed by thesystem
B. work performed uponthe system
C. heat supplied to the system
D. friction in the system
Answer» D. friction in the system
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

B. reversible & isothermal
C. frictionless & irreversible
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
54.

A. heat
B. work
C. enthalpy
D. entropy
55.

A. zero
B. minimum
C. maximum
D. infinite
56.

A. zero
B. unity
C. negative
D. positive
57.

A. zero
B. positive
C. negative
D. infinite
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

B. ideal fluid flow
D. frictionless reversible flo
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
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
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
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
67.

## The entropy may be expressed as a function of

A. pressure & temperature
B. temperature & volume
C. heat & work
D. all of the above
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
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
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
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
73.

## The reversible engines are

A. least efficient
B. most efficient
C. having same efficiency asirreversible engines
D. none of the above
74.

A. one
B. two
C. three
D. four
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
76.

## Second law of thermodynamics defines

A. work
B. heat
C. entropy
D. internal energy
77.

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

A. constant volume
B. polytropic
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
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
C. throttling
D. constant pressureexpansion
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. 20.5 %
B. 30.2%
C. 32.8%
D. 44.6%
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
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. 273 kj/s
B. 200 kj/s
C. 180 kj/s
D. 150 kj/s
86.

A. 1
B. 2
C. 3
D. 4
87.

A. 20%
B. 30%
C. 70%
D. 76.7%
88.

A. mlt ????
B. ml??t????
C. ml??t ????
D. ml??t ????
89.

A. 0.460 kw
B. 0.505 kw
C. 0.588 kw
D. 0.650 kw
90.

A. 100 kj
B. 60 kj
C. 40 kj
D. 88 kj
91.

A. 66 w
B. 56 w
C. 46 w
D. 36 w
92.

A. 100 kj
B. 1200 k
C. 1400 k
D. 800 k
93.

A. 25%
B. 27.5%
C. 30%
D. 33%
94.

## Choose the correct statement

A. pressure, temp. & entropy are extensiveproperties
B. pressure, temp. & entropy are intensiveproperties
C. pressure, volume & temp. are extensive properties
D. volume & entropy are extensive properties
Answer» D. volume & entropy are extensive properties
95.

## The second law of thermodynamics defines

A. heat
B. enthalpy
C. internal energy
D. entropy
96.

A. first
B. second
C. third
D. zeroeth
97.

A. isothermal
C. isentropic
D. thrittling
98.

A. 290 mw
B. 290 mj
C. 137.5 mw
D. 137.5 mj
99.

A. 60%
B. 62.5%
C. 65%
D. 37.5%
100.

A. 67%
B. 33%
C. 75%
D. 37.5%