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ESE - 19Mechanical Engineering

(Volume - I)(Thermal Engineering, Heat Transfer, Fluid Mechanics & Turbo Machinery)

Previous years Objective Questions with Solutions, Subject wise & Chapter wise(1992 − 2018)

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ForewordUPSC Engineering Services in MECHANICAL ENGINEERING

Volume - I Objective Questions: From 1992 – 2018

Currently, the Stage-I (Prelims) of ESE (Mechanical Engineering) consists of two objective

papers. Paper - I is for General Studies & Engineering Aptitude, while Paper-II is of

Mechanical Engineering for 300 Marks and for 3 hours duration. In stage-II (Mains)

Mechanical Engineering, the technical syllabus is divided into two papers which contain

Conventional Questions.

The Objective Questions included in this volume are for the following subjects only.

1. Thermal Engineering 2. Heat Transfer

3. Fluid Mechanics 4. Turbo machinery

Based on the new pattern for Prelims, Volume - I is redesigned using the previous questions from 1992

onwards for the above mentioned subjects.

The style, quality and content of the Solutions for previous ESE Questions of Mechanical Engineering, will

encourage the reader, especially the student whether above average, average or below average to learn the

concept and answer the question in the subject without any tension. However, it is the reader who should

confirm this and any comments and suggestions regarding this would be warmly received by the Academy.

It is observed that majority of ESE objective Questions are being asked as it is, in many PSUs, state service

commissions, state electricity boards and even in GATE exam. Hence, we strongly recommend all students who

are competing for various competitive exams to use this book according to the syllabus of the exam concerned.

This book can also be used by fresh Teachers in engineering colleges to improve their Concepts.

We proudly say that questions and solutions right from 1992 onwards are given in this book. The questions

which appeared in early 90’s are most conceptual oriented and these are being repeated in the recent exams

in a different way. Hence, we advise the students to practice these questions compulsorily. The student is also

advised to analyze why only a particular option is correct and why others are not. Evaluate yourself, in which

case, these other options are correct. With this approach you yourself can develop four questions out of one

question. The student is advised to solve the problems without referring to the solutions. The student has to

analyze the given question carefully, identify the concept on which it is framed, recall the relevant equations,

find out the desired answer, verify the answer with the final key such as (a), (b), (c), (d), then go through the

hints to clarify his/her answer. The student is advised to have a standard text book ready for reference to

strengthen the related concepts, if necessary. The student is further advised not to write the solution steps in

the space around the question. By doing so, one loses an opportunity of effective revision.

With best wishes to all those who wish to go through the following pages.

Y.V. Gopala Krishna Murthy,

M Tech. MIE,

Chairman & Managing Director,

ACE Engineering Academy,

ACE Engineering Publications.

Weightage of Subjects in Engineering Services Examination

MECHANICAL ENGINEERING

ESE – 2017 and 2018 (Prelims, Subjectwise Weightage)

SUBJECT 2017 2018

Thermal Engineering 45 53

Heat Transfer 07 07

Fluid Mechanics & Turbomachinery 17 19

Renewable Sources of Energy 03 01

Engineering Mechanics 05 04

Strength of Materials 11 08

Engineering Materials 08 11

Theory of Machines 23 16

Machine Design 06 03

Production Technology 10 07

Industrial Engineering & Operations Research 07 04

Maintenance Engineering 01 -

Mechatronics and Robotics 07 17

Total No. Marks 150 150

Previous years Questions with Solutions, Subject wise & Chapter wise MECHANICAL ENGINEERING (1992 – 2018)

MAIN INDEX

S.No. Name of the Subject Page No.

1 Thermal Engineering 01 - 486

2 Heat Transfer 487 - 606

3 Fluid Mechanics 607 - 840

4 Turbo machinery 841 - 907

PageNo.1

UPSC Engineering Service (ESE)

SYLLABUS

ThermalEngineering:

Thermodynamic systems and processes; properties of pure substance; Zeroth, First and Second

Laws of Thermodynamics; Entropy, Irreversibility and availability; analysis of thermodynamic

cycles related to energy conversion: Rankine, Otto, Diesel and Dual Cycles; ideal and real gases;

compressibility factor; Gas mixtures.

SI and CI Engines, Engine Systems and Components, Performance characteristics and testing of

IC Engines; Fuels; Emissions and Emission Control. Vapour compression refrigeration,

Refrigerants and Working cycles, Compressors, Condensers, Evaporators and Expansion devices,

Other types of refrigeration systems like Vapour Absorption, Vapour jet, thermo electric and

Vortex tube refrigeration. Psychometric properties and processes, Comfort chart, Comfort and

industrial air conditioning, Load calculations and Heat pumps. Steam and Gas Turbines, Theory

of Jet Propulsion – Pulse jet and Ram Jet Engines, Reciprocating and Rotary Compressors –

Theory and Applications.

Power Plant Engineering: Rankine and Brayton cycles with regeneration and reheat, Fuels and

their properties, Flue gas analysis, Boilers, steam turbines and other power plant components

like condensers, air ejectors, electrostatic precipitators and cooling towers – their theory and

design, types and applications;

Renewable sources of energy: Solar Radiation, Solar Thermal Energy collection - Flat Plate and

focusing collectors their materials and performance. Solar Thermal Energy Storage, Applications

– heating, cooling and Power Generation; Solar Photovoltaic Conversion; Harnessing of Wind

Energy, Bio-mass and Tidal Energy – Methods and Applications, Working principles of Fuel Cells.

PageNo.2

PreviousIESQuestions&Solutions

To ThermalEngineering

ChapterNo. NameoftheChapter Questions

PageNo.SolutionsPageNo.

01 Basic Concepts & Zeroth Law 05 – 12 13 – 18

02 Work & Heat 19 – 26 27 – 33

03 First Law 34 – 42 43 – 49

04 Second Law 50 – 64 65 – 81

05 Entropy 82 – 92 93 – 99

06 Availability 100 – 102 103 – 105

07 Properties of pure substances 106 – 118 119 – 127

08 Air Cycles 128 – 139 140 – 146

09 IC Engine 147 – 188 189 – 211

10 Fuels & Combustion 212 – 220 221 – 225

11 Thermodynamic Relations 226 – 230 231 - 233

CONTENTS

PageNo.3

PageNo.4

ChapterNo.

NameoftheChapter QuestionsPageNo.

SolutionsPageNo.

12 Psychrometry 234 – 251 252 – 265

13 Rankine Cycle 266 – 272 273 – 277

14 Gas Turbine 278 – 287 288 – 294

15 Refrigeration 295 – 322 323 – 341

16 Air Conditioning 342 – 350 351 – 357

17 Nozzles 358 – 365 366 – 369

18 Steam Turbines 370 – 386 387 – 398

19 Jet Propulsion 399 – 406 407 – 412

20 Reciprocating Air compressor 413 – 423 424 – 429

21 Centrifugal Compressor 430 – 436 437 – 441

22 Axial Flow Compressor 442 – 449 450 – 452

23 Boilers 453 – 465 466 – 471

24 Compressible fluid flow 472 – 478 479 – 483

25 Steam Condensers 484 – 484 485 – 485

26 Solar Energy 486 – 486 486 - 486

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BasicConcepts&ZerothLaw Chapter1

01. The number of degrees of freedom for a

diatomic molecule (ESE – 92)

(a) 2 (b) 3 (c) 4 (d) 5

02. Given:

P = Pressure.

T = Temperature.

v = Specific volume.

Which one of the following can be

considered as property of system?

(ESE – 93)

(a) Pdv

(b) dPv

(c)

v

dv.P

T

dT

(d)

T

dP.v

T

dT

03. Assertion (A): If an alcohol and a mercury

thermometer read exactly 0C at the ice

point and 100C at the steam point and the

distance between the two point is divided

into 100 equal parts in both thermometers,

the two thermometers will give exactly the

same reading at 50C.

Reason (R): Temperature scales are

arbitrary. (ESE– 95)

04. The correct sequence of the decreasing order

of the value of characteristic gas constants of

the given gases is (ESE – 95)

(a) hydrogen, nitrogen, air, carbon dioxide

(b) carbon dioxide, hydrogen, nitrogen, air

(c) air, nitrogen, carbon dioxide, hydrogen

(d) nitrogen, air, hydrogen, carbon dioxide.

05. Zeroth Law of thermodynamic systems state

that (ESE – 96)

(a) two thermodynamic systems are always

in thermal equilibrium with each other.

(b) if two systems are in thermal

equilibrium, then the third system will

also be in thermal equilibrium.

(c) two systems not in thermal equilibrium

with a third system, are also not in

thermal equilibrium with each other.

(d) when two systems are in thermal

equilibrium with a third system, they

are in thermal equilibrium with each

other.

06. Match List-I (Gadgets undergoing a

thermodynamic process) with List-II

(Property of the system that remains

constant) and select the correct answer using

the codes given below the List.

(ESE – 98)

: 6 : Thermal Engineering


List-I

A. Bomb calorimeter

B. Exhaust gas calorimeter

C. Junker gas calorimeter

D. Throttling calorimeter List-II

1. Pressure 2. Enthalpy

3. Volume 4. Specific heats

Codes:

A B C D

(a) 3 4 1 2

(b) 2 4 1 3

(c) 3 1 4 2

(d) 4 3 2 1 07. Which one of the following is the extensive

property of a thermodynamic system?

(ESE – 99)

(a) Volume (b) Pressure

(c) Temperature (d) Density

08. A closed thermodynamic system is one in

which (ESE – 99)

(a) There is no energy or mass transfer

across the boundary

(b) There is no mass transfer, but energy

transfer exists

(c) There is no energy transfer, but mass

transfer exists

(d) Both energy and mass transfer take

place across the boundary, but the mass

transfer is controlled by valves

09. In a new temperature scale say , the

boiling and freezing points of water at one

atmosphere are 100o and 300o

respectively. Correlate this scale with the

Centigrade scale. The reading of 0o on the

Centigrade is (ESE – 01)

(a) 0oC (b) 50oC

(c) 100oC (d) 150oC

10. Pressure reaches a value of absolute zero

(ESE – 02)

(a) at a temperature of –273 K

(b) under vacuum condition

(c) at the earth’s centre

(d) when molecular momentum of system

becomes zero

11. Consider the following statements:

(ESE – 03)

1) Zeroth law of thermodynamics is related

to temperature.

2) Entropy is related to first law of

thermodynamics.

3) Internal energy of an ideal gas is a

function of temperature and pressure.

4) Vander Waals’ equation is related to an

ideal gas.

Which of the above statements is/are

correct?

(a) 1 only (b) 2, 3 and 4

(c) 1 and 3 (d) 2 and 4

: 7 : Basic Concepts & Zeroth Law


12. Which one of the correctly defines 1 K, as

per the internationally accepted definition of

temperature scale? (ESE – 04)

(a) 1

100th of the difference between normal

boiling point and normal freezing point

of water

(b) 1

273.15th of the normal freezing point

of water

(c) 100 times the difference between the

triple point of water and the normal

freezing point of water.

(d) 16.273

1 th of the triple point of water.

13. Which of the following are intensive

properties? (ESE – 05)

1. Kinetic Energy

2. Specific enthalpy

3. Pressure

4. Entropy

Select the correct answer using the code

given below:

(a) 1 and 3 (b) 2 and 3

(c) 1, 3 and 4 (d) 2 and 4

14. A thermoelectric engine which consists of

dissimilar electric conductors connected at

two junctions maintained at different

temperatures, converts (ESE – 06)

(a) Electric energy into heat energy

(b) Heat energy into electric energy

(c) Mechanical work into electric energy

(d) Electric energy into mechanical work

15. Which of the following are intensive

properties? (ESE – 07)

1. Kinetic energy

2. Thermal conductivity

3. Pressure

4. Entropy

Select the correct answer using the code

given below:

(a) 1 and 2 (b) 2 and 3 only

(c) 2, 3 and 4 (d) 1, 3 and 4

16. Match List I with List II and select the

correct answer using the code given below

the lists: (ESE – 07)

List – I (Type of Thermometer)

A. Mercury-in-glass

B. Thermocouple

C. Thermistor

D. Constant volume gas

List – II (Thermometric Property)

1. Pressure

2. Electrical resistance

3. Volume

4. Induced electric voltage



Codes:

A B C D

(a) 1 4 2 3

(b) 3 2 4 1

(c) 1 2 4 3

(d) 3 4 2 1

17. Measurement of temperature is based on

which law of thermodynamics?

(ESE – 09)

(a) Zeroth law of thermodynamics

(b) First law of thermodynamics

(c) Second law of thermodynamics

(d) Third low of thermodynamics

18. Consider the following properties:

(ESE – 09)

1. Temperature

2. Viscosity

3. Specific entropy


Which of the above properties of a system

is/are intensive?

(a) 1 only (b) 2 and 3 only

(c) 2, 3 and 4 only (d) 1, 2, 3 and 4

19. Consider the following properties:

(ESE – 09)

1. Entropy

2. Viscosity

3. Temperature

4. Specific heat at constant volume

Which of the above properties of system

is/are extensive?

(a) 1 only (b) 1 and 2 only

(c) 2, 3 and 4 (d) 1, 2 and 4

20. Ice kept in a well insulated thermo flask is

an example of which system? (ESE – 09)

(a) Closed system

(b) Isolated system

(c) Open system

(d) Non-flow adiabatic system

21. Consider the following: (ESE – 10)

1. Kinetic energy

2. Entropy


4. Pressure

Which of these are intensive properties?

(a) 1, 2 and 3 only (b) 2 and 4 only

(c) 3 and 4 only (d) 1, 2, 3 and 4

22. Consider the following: (ESE – 10)

1. Temperature

2. Viscosity

3. Internal energy

4. Entropy

Which of these are extensive properties?

(a) 1, 2, 3 and 4

(b) 2 and 4 only

(c) 2 and 3 only

(d) 3 and 4 only



23. The Zeroth law of thermodynamics states

that (ESE – 10)

(a) Two thermodynamic systems are always

in thermal equilibrium with each other

(b) If two systems are in thermal

equilibrium, then the third system will

also be in thermal equilibrium.

(c) Two systems not in thermal equilibrium

with a third system are also not in

thermal equilibrium with each other.

(d) When two systems are in thermal

equilibrium with a third system, they

are in thermal equilibrium with each

other.

24. Hot coffee stored in a well insulated thermos

flask is an example of (ESE – 10)

(a) Isolated system

(b) Closed system

(c) Open system

(d) Non-flow adiabatic system.

25. A control volume is (ESE– 10)

(a) An isolated system

(b) A closed system but heat and work can

cross the boundary

(c) A specific amount of mass in space

(d) A fixed region in space where mass,

heat and work can cross the boundary

of that region.

26. A closed thermodynamic system manifests

when (ESE – 10)

(a) Matter is not allowed to cross the

boundary but energy transfer occurs

across the boundary

(b) There is transfer of both mass and

energy across the system boundaries

(c) There is only transfer of mass but no

heat and work energy are transferred

(d) There is absolutely no interaction of the

system with surroundings.

27. Which one of the following represents open

thermodynamic system? (ESE – 11)

(a) Manual ice cream freezer

(b) Centrifugal pump

(c) Pressure cooker

(d) Bomb calorimeter

28. A thermodynamic system is considered to be

an isolated one if (ESE – 11)

(a) Mass transfer and entropy change are

zero

(b) Entropy change and energy transfer are

zero

(c) Energy transfer and mass transfer are

zero

(d) Mass transfer and volume change are

zero



29. Match List I with List II and select the

correct answer using the code given below

the lists: (ESE – 11)

List I

A. Interchange of matter is not possible in a

B. Any processes in which the system

returns to its original condition or state

is called

C. Interchange of matter is possible in a

D. The quantity of matter under

consideration in thermodynamics is

called

List II

1. Open system

2. System

3. Closed system

4. Cycle

Code:

A B C D

(a) 2 1 4 3

(b) 3 1 4 2

(c) 2 4 1 3

(d) 3 4 1 2

30. A closed system is one in which

(ESE – 11)

(a) Mass does not cross boundaries of the

system, though energy may do so

(b) Mass crosses the boundary but not the

energy

(c) Neither mass nor energy cross the

boundary of the system

(d) Both energy and mass cross the

boundaries of the system

31. The constant volume gas thermometer works

on the principle that (ESE – 12)

(a) at low pressure, the temperature of the

gas is independent of its pressure at

constant volume

(b) at high pressure, the temperature of the

gas is independent of its pressure at

constant volume

(c) at low pressure, the temperature of the

gas is proportional to its pressure at

constant volume

(d) at high pressure, the temperature of the

gas is proportional to its pressure at

constant volume

32. In highly rarefied gases, the concept of this

loses validity (ESE – 12)

(a) Thermodynamic equilibrium

(b) Continuum

(c) Stability

(d) Macroscopic view point

33. Which one of the correctly defines 1 K, as

per the internationally accepted definition of

temperature scale? (ESE – 04)

(a) 1

100th of the difference between normal

boiling point and normal freezing point

of water



(b) 1

273.15th of the normal freezing point

of water

(c) 100 times the difference between the

triple point of water and the normal

freezing point of water.

(d) 16.273

1 th of the triple point of water.

34. Assertion (A): The mass flow rate through a

compressor for various refrigerants at same

temperature and pressure, is proportional to

their molecular weights.

Reason(R): According to Avogadro’s law

all gases have same number of moles in a

given volume at same pressure and

temperature. (ESE – 02)

35. The value of an extensive property is

essentially dependent on (ESE – 13)

(a) mass of the system

(b) interaction of the system with its

surroundings

(c) path followed by the system in going

from one state to another

(d) nature of boundaries, rigid or flexible

36. If the time taken by a system to execute a

process through a finite gradient is infinitely

large, the process (ESE – 13)

(a) becomes reversible (b) is irreversible

(c) becomes isothermal (d) is adiabatic

37. Which of the following thermodynamic

properties are intensive properties?

(ESE – 14)

1. Density

2. Entropy

3. Viscosity

(a) 1, 2 and 3

(b) 1 and 2 only

(c) 2 and 3 only

(d) 1 and 3 only

38. Statement (I) : In an Isolated system, the

heat transfer Q and the work transfer W

are always zero.

Statement (II) : In an Isolated system, the

entropy always remains constant.

(ESE – 15)

39. Consider the following processes:

1. Extension of a spring

2. Plastic deformation of a material

3. Magnetization of a material exhibiting

hysteresis

Which of the above processes are

irreversible? (ESE – 16)

(a) 1 and 2 only

(b) 1 and 3 only

(c) 2 and 3 only

(d) 1, 2 and 3



40. 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

process.

2. All the processes, taking place in the

cycle, must be extremely slow.

3. The working parts of the engine must be

friction free.

Which of the above conditions are correct?

(ESE – 16)

(a) 1, 2 and 3 (b) 1 and 2 only

(c) 1 and 3 only (d) 2 and 3 only

41. The property of a thermodynamic system is:

(ESE – 16)

(a) A path function

(b) A point function

(c) A quantity which does not change in

reversible process

(d) A quantity which changes when system

undergoes a cycle

42. Statement (I): Thermometers using

different thermometric property substance

may give different readings except at two

fixed points.

Statement (II): Thermodynamic

temperature scale is independent of any

particular thermometric substance.

(ESE – 16)

43. Which one of the following substances has

constant specific heat at all pressures and

temperatures?

(ESE – 18)

(a) Mono-atomic gas

(b) Di-atomic gas

(c) Tri-atomic gas

(d) Poly-atomic gas



KEY SHEET

01. (d) 02. (d) 03. (d) 04. (a) 05. (d) 06. (a) 07. (a) 08. (b) 09. (d) 10. (d)

11. (a) 12. (d) 13. (b) 14. (b) 15. (b) 16. (d) 17. (a) 18. (d) 19. (a) 20. (b)

21. (c) 22. (d) 23. (d) 24. (a) 25. (d) 26. (a) 27. (b) 28. (c) 29. (d) 30.(a)

31. (c) 32.(b) 33. (d) 34. (a) 35.(a) 36.(a) 37. (d) 38.(c) 39.(c) 40.(a)

41.(b) 42.(b) 43.(a)

01. Ans: (d)

Sol:

Monoatomic gases have 3 degrees of

freedom.

3 – Translational motions

Diatomic molecules have 5 degrees of

freedom.

3 – Translational motions

2 – Rotational motions

02. Ans: (d)

Sol: dPT

v

T

dT

= dPP

RdT

T

1

= NdPMdT

where, M = ;T

1

P

RN

Also, 0T

N;0

P

M

T

N

P

M

exact differential is a point

function and a property of the system.

03. Ans: (d)

Sol: Boiling point of Alcohol is 780C. Boiling

point of Mercury is 3570C.

04. Ans: (a)

Sol: Characteristic gas constant,

R = M

R

where, R = Universal gas constant

M = Molecular weight

Also, 222 COAirNH MMMM

222 COAirNH RRRR

SOLUTIONS



05. Ans: (d)

Sol: When a body A is in thermal equilibrium

with a body B, and also separately with a

body C, then B and C will be in thermal

equilibrium with each other. This is known

as zeroth law of thermodynamics.

06. Ans: (a)

Sol:

Bomb calorimeter is a type of constant

volume calorimeter used in measuring the

heat of combustion of a particular reaction.

Throttling calorimeter is an instrument

utilizing the principle of constant enthalpy

expansion for the measurement of moisture

content of steam.

07. Ans: (a)

Sol: Extensive property is dependant on mass.

e.g. Volume, Energy

08. Ans: (b)

Sol:

Closed system, which allows the transfer of

energy but not mass. e.g. Pressure cooker.

Open system can exchange mass and

energy. e.g. Air compressor, centrifugal

pump.

Isolated system, which does not allow the

transfer of either mass or energy. e.g. A

well insulated thermo flask.

09. Ans: (d)

Sol: Given data:

scale C scale

Boiling point: 100 100C

Freezing point: 300 0C

LFPUFP

LFP

LFPUFP

LFPC

where, LFP = Lower Fixed Point

UFP = Upper Fixed Point

300100

3000

0100

0C C = 150

10. Ans: (d)

Sol: Pressure measured of a system is nothing

but the thrust exerted by movement of

molecules in contact. When molecular

momentum becomes zero pressure reaches a

value of absolute zero.

11. Ans: (a)

Sol:

Van Der Waals equation is for real gases.

Internal energy of ideal gas is a function

of temperature only.

Entropy is related to second law of

thermodynamics.

12. Ans: (d)

Sol: 16.273

1K1 of triple point of water.



13. Ans: (b)

Sol: Intensive property is independent of mass.

Any specific extensive property is an

intensive property.

e.g. Pressure, Temperature, Specific

volume, Specific enthalpy.

14. Ans: (b)

Sol: According to seebeck effect, a temperature

difference between two dissimilar electrical

conductors or semi conductors produces a

voltage difference between the two

substances. It indicated conversion of heat

energy into electric energy.

15. Ans: (b)

Sol: Refer to the solution of Q. No. 13.

16. Ans: (d)

Sol:

In mercury-in-glass thermometer, the

volume of mercury changes slightly with

temperature. This change in volume is used

as a property to indicate temperature scale

of this thermometer.

Due to the see beck effect, a net e.m.f is

generated in the thermocouple circuit which

depends on the difference in temperature

between the hot and cold junctions and is,

therefore, a thermometric property of the

circuit.

A thermistor is a resistance thermometer, or

a resistor whose resistance is dependent on

temperature.

From the law of Gay-Lussac, we know that

temperature of an ideal gas is directly

proportional to its pressure. Constant

volume gas thermometer operates on the

same principle, with the restrictions that the

gas is at low pressure.

17. Ans: (a)

Sol: Significance of Zeroth law is it gives the

concept of temperature and defines an

isotherm.

18. Ans: (d)


19. Ans: (a)


20. Ans: (b)

Sol: Thermo flask is an example of isolated

system. Also, refer to the solution of

Question No. 08.

21. Ans: (c)


22. Ans: (d)




23. Ans: (d)


24. Ans: (a)


25. Ans: (d)

Sol: When there is matter flow in the system,

then the system is considered to be a

volume of fixed identify, the control

volume. There is no difference between an

open system and a control volume.

26. Ans: (a)


27. Ans: (b)

Sol: Water enters and leaves centrifugal pump.

Also, refer to the solution of Q. No. (08).

28. Ans: (c)

Sol: For isolated system there is no mass or

energy transfer. Also, refer to the solution

of Q. No. (08).

29. Ans: (d)

Sol:

Interchange of matter is not possible in

closed system.

Interchange of matter is possible in open

system.

Quantity of matter under consideration in

thermodynamics is called a system.

Any process in which the system returns to

its original state is called cycle.

30. Ans: (a)

Sol: For a closed system there is only energy

transfer but no mass transfer. Also, refer to

the solution of Q. No. (08).

31. Ans: (c)

Sol: Pressures used are low. Also, refer to the

solution of Q. No. (16).

32. Ans: (b)

Sol: The density of a system at a point is,

V

mlim

VV

At volumes less than V Molecular domain

The smallest volume which may be

regarded as continuous is V.

Concept of continuum looses its validity

when mean free path of molecules

approach dimensions of vessel.

P

Domain of Molecular effects

V

V

m

Domain of continuum

V



Examples: highly rarefied gases in high

vacuum technology in rocket flights at

high altitudes and electron tubes.

33. Ans: (d)

Sol: 16.273

1K1 of triple point of water.

34. Ans: (a)

Sol: Avogadro’s law is equal volume of all gases

under similar conditions of temperature and

pressure have equal number of molecules.

35. Ans: (a)


36. Ans: (a)

Sol: Time has an important effect on

reversibility. If the time allowed for a

process to occur is infinitely large, even

though the gradient is finite, the process

becomes reversible.

However, if this time is squeezed to a finite

value, the finite gradient makes the process

irreversible.

37. Ans: (d)

Sol: Entropy is an extensive property. Hence it is

not correct. Also, refer to the solution of

Question No. (13).

38. Ans: (c)

Sol: For an isolated system entropy always

increases and becomes a maximum at the

state of equilibrium.

39. Ans: (c)

Sol: A reversible process is one which is

performed in such a way that at the

conclusion of the process, both the system

and the surroundings may be restored to

their initial stages, without producing any

changes in the rest of the universe.

Thus, extension of a spring is reversible

process. But, plastic deformation of a

material and magnetization of a material

exhibiting hysteresis are irreversible

processes.

40. Ans: (a)

Sol: For reversibility dP = 0, dT = 0. All

processes should be quasi-static which

implies extremely slow, friction should not

be present.

41. Ans: (b)

Sol: For a thermodynamic system, property is a

point function and change in the property is

zero if the system undergoes a cycle.



43. Ans: (a)

Sol: Mono atomic gases behave as ideal gas as

they are having three degrees of freedom in

which all are translational motion (Due to

vibrational and rotational motion existing

between the atoms in the molecule, they

tend to change with temperature and

pressure as interaction between them

changes).

ace prelims... · 1. thermal engineering 2. heat transfer 3. fluid mechanics 4. turbo machinery...

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