Physics previous year question Of Thermodynamics for NDA

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previous year question Of Thermodynamics for NDA

Previous year questions

Q 2878034806

Consider the following types of surfaces
A surface that is

I. coated with lamp black

II. polished

III. painted white

The correct sequence of the decreasing order of the emissive
powers of the given surfaces will be

(A)

I, III, II

(B)

III, II, I

(C)

II, I,III

(D)

II, III , I

Solution:

Correct Answer is `=>` (A) I, III, II

Q 2858034804

Which of the following are factors upon which the amount of heat
radiated from a body depends?

I. Excess temperature of the body
over surroundings.

II. Density of the body.

III. Exposed area of the body.

IV. Nature of the surface of the body
Choose the correct answer from the
codes given below

(A)

I, II and Ill

(B)

I, II and IV

(C)

I, Ill and IV

(D)

II, II II and IV

Solution:

Correct Answer is `=>` (C) I, Ill and IV

Q 2808634508

Consider the following statements about a thermos flask.

I. It is a practical device in which the heat flowing into or·
out of the system by conduction. convection or
radiation is reduced as much as possible.

II. It consists of a doublewalled glass vessel.

III. In a thermos flask, the heat transfers by convection is
minimised by silvering the surfaces and that by radiatior is minimined by evacuating the
space between the walls. Of these statements

(A)

Both II and Ill

(B)

Both I and II

(C)

Both I and III

(D)

I, II and Ill

Solution:

Correct Answer is `=>` (A) Both II and Ill

Q 2868634505

The pressure and density of a diatomic gas changes adiabatically
from `(p, ρ) tc (p ', ρ' )`. If `(ρ')/p` is equal to 32, then `(p')/(p)` should be

(A)

128

(B)

(C)

1/128

(D)

Solution:

Correct Answer is `=>` (D) 32

Q 2858634504

If a gas is heated at constant pressure, then its isothermal
compressibility

(A)

increases with temperature

(B)

remains constant

(C)

decreases with temperature

(D)

decreases inversely with temperature

Solution:

Correct Answer is `=>` (B) remains constant

Q 2808534408

Resistance of a conductor varies
with temperature in a manner

(A)

`R_T = R_0 (1+ alpha^2 t )`

(B)

`R_t = R_0 (1+ alpha t )`

(C)

`R_t= R_0 (1+ alpha t )^2`

(D)

`R_t = R_0 (1- alpha t )`

Solution:

Correct Answer is `=>` (B) `R_t = R_0 (1+ alpha t )`

Q 2878534406

Luminosity of rigel star in orion constellation is 17000 times that
of our sun. lf the surface temperature of sun is 6000 K,
then the temperature of the star is about

(A)

18000 K

(B)

68500 K

(C)

7000 k

(D)

8000 K

Solution:

Correct Answer is `=>` (B) 68500 K

Q 2868534405

The temperature of the stars can
be estimated by

(A)

Wien's displacement law

(B)

Rayleigh-Jeans law

(C)

Faraday's law

(D)

Maxwell-Boltzmann law

Solution:

Correct Answer is `=>` (A) Wien's displacement law

Q 2858534404

Which one of the following is the mode of heat transfer in which
warm material is transported, so as to displace a cooler material?

(A)

Conduction only

(B)

Convection only

(C)

Radiation

(D)

Both conduction and convection

Solution:

Correct Answer is `=>` (B) Convection only

Q 2848534403

A fan produces a feeling of comfort during hot weather
because

(A)

our body radiates more heat in air

(B)

fan supplies cool air

(C)

conductivity of air increase

(D)

our perspiration evaporates rapidly

Solution:

Correct Answer is `=>` (D) our perspiration evaporates rapidly

Q 2818434309

Four rods of length land radius r of the same material are kept at
the same temperature. Which of the rods conduct most heat?

(A)

l = 2 m , r = 10 cm

(B)

l = 2 m, r = 5 cm

(C)

l =1m, r = 5 cm

(D)

l =1 m, r = 10 cm

Solution:

Correct Answer is `=>` (D) l =1 m, r = 10 cm

Q 2888434307

An iron mass falls from a height of 1 km on the ground. If all the
energy is converted into heat, then the rise of temperature of
the mass will be

(A)

`2.33^o C`

(B)

`0.233^o C`

(C)

`23.3^o C`

(D)

`233^o C`

Solution:

Correct Answer is `=>` (A) `2.33^o C`

Q 2858434304

If the temperature of sun becomes
twice its present temperatures, then

(A)

radiated energy would be predominantly in ultraviolet region

(B)

radiated energy would be predominantly in infrared region

(C)

radiated energy would be predominantly in X-ray region

(D)

radiated energy would become twice the present radiated energy

Solution:

Correct Answer is `=>` (A) radiated energy would be predominantly in ultraviolet region

Q 2818434300

On increasing the temperature of a substance gradually, one notice
the colour

(A)

blue

(B)

green

(C)

red

(D)

yellow

Solution:

Correct Answer is `=>` (C) red

Q 2878334206

Air is blown over a hot body to cool it. This would increase the
rate of heat loss by

(A)

conduction

(B)

radiation and convection

(C)

convection

(D)

Both conduction and convection

Solution:

Correct Answer is `=>` (C) convection

Q 2828234101

Four hot metallic articles which are coloured as blue, red, black
and white but have the same temperature and then they are
allowed to cool. Which will have the fastest cooling rate?

(A)

white

(B)

Red

(C)

Blue

(D)

Black

Solution:

Correct Answer is `=>` (A) white

Q 2888123907

A gas filled cylinder fitted with a piston is immersed it ice at `0^o` C.
The piston is rapidly pushed down to compress the gas which
is therefore heated. It is then left for sometime, so that the gas is
once again reaches at `0^o` C. The piston is now slowly raised upto
the initial position. 100 g of ice is melted during this process, the
work done on the gas is

(A)

60 cal

(B)

80 cal

(C)

800 cal

(D)

8000 cal

Solution:

Correct Answer is `=>` (D) 8000 cal

Q 2828123901

A number of small drops of Hg adiabatically coalesce to form a
single drop. The temperature of the drop will

(A)

decrease

(B)

remain same

(C)

increase

(D)

depend on size

Solution:

Correct Answer is `=>` (C) increase

Q 2808623508

An ideal heat engine absorbs heat at a temperature `150^o` C and
its exhaust temperature is `50^o` C. The efficiency of heat engine is

(A)

23.64%

(B)

50%

(C)

20%

(D)

25%

Solution:

Given,

`T_1 = 150^o C = 150 + 273 = 423K`

`T_2 = 50^o C = 50 + 273 = 323K`

Efficiency of heat engine is given by

`η = (1- T_2/T_1) = (1- 323/323) ( (423 - 323 )/423)`

`= 0.236 =23.6 %`

Correct Answer is `=>` (A) 23.64%

Q 2888523407

A Carnot engine works between `100^o ` C and `20^o` C. lts efficiency is

(A)

1944.7%

(B)

0.21447%

(C)

200%

(D)

21.4%

Solution:

Given,

`T_1 = 100^o C = 100 + 273 = 373 K`

`T_2 = 20^o C = 20 + 273 = 293 K`

Efficiency of cannot engine is given by

` η = (1- T_2/T_1) = (1- (293)/(373)) = ( (373 - 293)/(373) )`

`= 0.214 = 21.47%`

Correct Answer is `=>` (D) 21.4%

Q 2868223105

In a Carnot engine, when heat is taken by a perfect gas from the
source, then the temperature of the source

(A)

decreases

(B)

increases

(C)

remains constan

(D)

None of these

Correct Answer is `=>` (B) increases

Q 2848112903

The internal energy U is unique function of any state because
change in U

(A)

depends upon path

(B)

does not depend upon path

(C)

corresponds to an isothermal process

(D)

corresponds to c n adiabatic process

Correct Answer is `=>` (C) corresponds to an isothermal process

Q 2838012802

If `gamma` denotes the ratio of the two specific heat of a gas, then the
ratio of the slopes of adiabatic and isothermal p-V curves at
their point of intersection is

(A)

`1/(gamma +1 )`

(B)

`1/(gamma )`

(C)

`gamma -1`

(D)

`gamma`

Correct Answer is `=>` (A) `1/(gamma +1 )`

Q 2808812708

The internal energy of a gram molecule of an ideal gas
depends on

(A)

only volume

(B)

only temperature

(C)

only pressure

(D)

Both pressure as well as temperature

Correct Answer is `=>` (B) only temperature

Q 2838812702

The mode of propagation of heat from the sun to the earth is

(A)

conduction alone

(B)

convection alone

(C)

radiation alone

(D)

Both convection and radiation

Correct Answer is `=>` (C) radiation alone

Q 2818812700

The blackboard seems black because it

(A)

reflects every colour

(B)

does not reflect any colour

(C)

absorbs black colour

(D)

reflects black colour

Correct Answer is `=>` (B) does not reflect any colour

Q 2888712607

The blackboard seems black because it

(A)

reflects every colour

(B)

does not reflect any colour

(C)

absorbs black colour

(D)

reflects black colour

Correct Answer is `=>` (B) does not reflect any colour

Q 2844178953

Consider the following types of surfaces
A surface that is
I. coated with lamp black
II. polished
III. painted white

The correct sequence of the decreasing order of the emissive powers of the given surfaces will be

(A)

I, III, II

(B)

III, II, I

(C)

II, I, III

(D)

II, III, I

Correct Answer is `=>` (A) I, III, II

Q 2824178951

Which of the following are factors upon which the amount of heat radiated from a body depends?

I. Excess temperature of the body over surroundings.

II. Density of the body.

III. Exposed area of the body

IV. Nature of the surface of the body

Choose the co :rect answer from the codes given below

(A)

I, II and Ill

(B)

I, II and IV

(C)

I, Ill and IV

(D)

II, III and IV

Correct Answer is `=>` (C) I, Ill and IV

Q 2804078858

Consider the following statements about a thermos flask.

I. It is a practical device in which the heat flowing into or out of the system by conduction. convection or radiation is reduced as much as possible.

II. It consists of a double walled glass vessel.

III. In a thermos flask, the heat transfers by convection is minimised by silvering the surfaces and that by radiatior is minimined by evacuating the space between the walls.

Of these statements

(A)

Both II and Ill

(B)

Both I and II

(C)

Both I and III

(D)

I, II and Ill

Correct Answer is `=>` (A) Both II and Ill

Q 2844078853

The pressure and density of a diatomic gas changes adiabaticaJy from (p, p) tc (p', p' ). If p'/p is equal to 32, lhen p'/p should be

(A)

128

(B)

(C)

1/128

(D)

Correct Answer is `=>` (D) 32

Q 2824078851

If a gas is heated at constant pressure, then its isothermal compressibility

(A)

increases with temperature

(B)

remains constant

(C)

decreases with temperature

(D)

decreases inversely with temperature

Correct Answer is `=>` (B) remains constant

Q 2874878756

Resistance of a conductor varies with temperature in a manner

(A)

`R_t = R_0 (1 + alpha t)`

(B)

`R_t = R_0 ( 1 + alpha t )`

(C)

`R_t = R_0 ( 1 + alphat)^2`

(D)

`R_t = R_0 ( 1 - alpha t ) `

Correct Answer is `=>` (B) `R_t = R_0 ( 1 + alpha t )`

Q 2814778659

Luminosity of rigel star in orion constellation is 17000 times that of our sun. lf the surface temperature of sun is 6000 K, then the temperature of the star is about

(A)

18000 K

(B)

68500 K

(C)

7000 K

(D)

8000 K

Correct Answer is `=>` (B) 68500 K

Q 2804778658

The temperature of the stars can be estimated by

(A)

Wien's displacement law

(B)

Rayleigh-Jeans law

(C)

Faraday's law

(D)

Maxwell-Boltzmann law

Correct Answer is `=>` (A) Wien's displacement law

Q 2884778657

Which one of the following is the mode of heat transfer in which warm material is transported, so as to displace a cooler material?

(A)

Conduction only

(B)

Convection only

(C)

Radiation

(D)

Both conduction and convection

Correct Answer is `=>` (B) Convection only

Q 2874778656

Which one of the following is the mode of heat transfer in which warm material is transported, so as to displace a cooler material?

(A)

Conduction only

(B)

Convection only

(C)

Radiation

(D)

Both conduction and convection

Correct Answer is `=>` (B) Convection only

Q 2844778653

A fan produces a feeling of comfort during hot weather because

(A)

our body radiates more heat in air

(B)

fan supplies cool air

(C)

conductivity of air increase

(D)

our perspiration evaporates rapidly

Correct Answer is `=>` (D) our perspiration evaporates rapidly

Q 2834678552

Two bodies A and Bare placed in an evacuated vessel maintained at a temperature of 27°C. The temperature of A is 327°C and
that of B is 227°C. The ratio of heat loss from A and B is about

(A)

1 : 2

(B)

2 : 8

(C)

8 : 2

(D)

2 : 1

Correct Answer is `=>` (D) 2 : 1

Q 2874578456

Four rods of length land radius r of the same material are kept at the same temperature. Which of the rods conduct most heat?

(A)

l = 2 m,r = 10 cm

(B)

l = 2m, r = 5 cm

(C)

l =1 m, r = 5 cm

(D)

l =1m, r = 10 cm

Correct Answer is `=>` (D) l =1m, r = 10 cm

Q 2804478358

An iron mass falls from a height of 1 km on the ground. If all the energy is converted into heat, then the rise of temperature of the mass will be

(A)

2.33°C

(B)

0.233°C

(C)

23.3°C

(D)

233°C

Correct Answer is `=>` (A) 2.33°C

Q 2864378255

If the temperatuxe of sun becomes twice its present temperatures, then

(A)

radiated energy would be predominantly in ultraviolet region

(B)

radiated energy would be predominantly in infrared region

(C)

radiated energy would be predominantly in X-ray region

(D)

radiated energy would become twice the present radiated energy

Correct Answer is `=>` (A) radiated energy would be predominantly in ultraviolet region

Q 2824378251

On increasing the temperature of a substance gradually, one notice the colour

(A)

blue

(B)

green

(C)

red

(D)

yellow

Correct Answer is `=>` (C) red

Q 2804278158

Air is blown over a hot body to cool it. This would increase the rate of heat loss by

(A)

conduction

(B)

radiation and convection

(C)

convection

(D)

Both conduction and convection

Correct Answer is `=>` (C) convection

Q 2814178059

Four hot metallic articles which are coloured as blue, red, black and white but have the same temperature and then they are allowed to cool. Which will have the fastest cooling rate?

(A)

White

(B)

Red

(C)

Blue

(D)

Black

Correct Answer is `=>` (A) White

Q 2874178056

A gas filled cylinder fitted with a piston is immersed it ice at 0°C. The piston is rapidly pushed down to compress the gas which is therefore heated. It is then left for sometime, so that the gas is once again reaches at 0°C. The piston is now slowly raised upto the initial position. 100 g of ice is melted during this process, the work done on the gas is

(A)

60 cal

(B)

80 cal

(C)

800 cal

(D)

8000 cal

Correct Answer is `=>` (D) 8000 cal

Q 2814167959

A number of small drops of Hg adiabatically coalesce to form a single drop. The temperature of the drop will

(A)

decrease

(B)

remain same

(C)

increase

(D)

depend on size

Correct Answer is `=>` (C) increase

Q 2854167954

1 L of a.ir at 76 cm of Hg iscompressed to a r.ressure of 120 cm of Hg under isothermal condition. The new volume is

(A)

`633.3 cm^3`

(B)

`6.33cm^3`

(C)

`76 crn^3`

(D)

`19 cm^3`

Solution:

`:. 1 L = 10^3 cm^3`

In isothermal condition, `p_1V_1 =p_2V_2`

`V_2 = (p_1V_1)/p_2 = (76 xx 10^3)/120 = 633.3 cm^3`

Correct Answer is `=>` (A) `633.3 cm^3`

Q 2854067854

An ideal heat engine absorbs heat at a temperature 150°C and its exhaust temperature is 50°C. The efficiency of heat engine is

(A)

23.64%

(B)

50%

(C)

20%

(D)

25%

Solution:

Given,

`T_1 = 150^oC = 150 + 273 = 423K`

`T_2 = 50°C = 50 + 273 = 323K`

Efficiency of heat engine is given by

`eta = (1 - T_2/T_1) =(1 - 323/423) (( 423 -323)/423)`

`= 0.236 = 23.6 %`

Correct Answer is `=>` (A) 23.64%

Q 2844867753

A Carnot engine works between 100°C and 20°C. lts efficiency is

(A)

1944.7%

(B)

0.21447%

(C)

200%

(D)

21.4%

Solution:

Given,

`T_1 = 100^oC = 100 + 273 = 373K`

`T_2 = 20°C = 20 + 273 = 293K`

Efficiency of carnot engine is given by

`eta =(1 - T_2/T_1) = ( 1 - 293/373) = ( (373 -293)/373)`

`=0.214 =21.47 %`

Correct Answer is `=>` (D) 21.4%

Q 2874767656

The source and sink temperatures of a Carnot engine are 400 K and 300 K, its efficiency is

(A)

50%

(B)

25%

(C)

30%

(D)

100%

Solution:

We know that, efficiency of Carnot engine,

`eta =1 - T_2/T_1 => eta = 1 - 300/400`

[given `T_2 = 300 K, T_1 = 400 K`]

`=(400 -300)/400 = 100/400 =1/4 =25 %`

Correct Answer is `=>` (B) 25%

Q 2884667557

In a Carnot engine when heat is taken by a perfect gas from the source, then the temperature of the sou:rce

(A)

decreases

(B)

increses

(C)

Remains constant

(D)

None of these

Solution:

We know that, efficiency of Carnot engine,

`eta =1 - T_2/T_1 => eta = 1 - 300/400`

[given `T_2 = 300 K, T_1 = 400 K`]

`=(400 -300)/400 = 100/400 =1/4 =25 %`

Correct Answer is `=>` (B) increses

Q 2824667551

The internal energy U is unique function of any state because change in U

(A)

depends upon path

(B)

does not depend upon path

(C)

corresponds to an isothermal process

(D)

corresponds to an adiabatic process

Solution:

We know that, efficiency of Carnot engine,

`eta =1 - T_2/T_1 => eta = 1 - 300/400`

[given `T_2 = 300 K, T_1 = 400 K`]

`=(400 -300)/400 = 100/400 =1/4 =25 %`

Correct Answer is `=>` (C) corresponds to an isothermal process

Q 2804567458

If `gamma` denotes the ratio of the two specific heat of a gas, then the ratio of the slopes of adiabatic and isothermal p-V curves at their point of intersection is

(A)

`1/(gamma +1 )`

(B)

`1/gamma`

(C)

`gamma -1`

(D)

`gamma`

Solution:

We know that, efficiency of Carnot engine,

`eta =1 - T_2/T_1 => eta = 1 - 300/400`

[given `T_2 = 300 K, T_1 = 400 K`]

`=(400 -300)/400 = 100/400 =1/4 =25 %`

Correct Answer is `=>` (A) `1/(gamma +1 )`

Q 2834567452

The internal energy of a gram molecule of an ideal gas depends on

(A)

only volume

(B)

only temperature

(C)

only pressure

(D)

Both pressure as well as temperature

Solution:

We know that, efficiency of Carnot engine,

`eta =1 - T_2/T_1 => eta = 1 - 300/400`

[given `T_2 = 300 K, T_1 = 400 K`]

`=(400 -300)/400 = 100/400 =1/4 =25 %`

Correct Answer is `=>` (B) only temperature

Q 2814567450

The internal energy of a gram molecule of an ideal gas depends on

(A)

only volume

(B)

only temperature

(C)

only pressure

(D)

Both pressure as well as temperature

Solution:

We know that, efficiency of Carnot engine,

`eta =1 - T_2/T_1 => eta = 1 - 300/400`

[given `T_2 = 300 K, T_1 = 400 K`]

`=(400 -300)/400 = 100/400 =1/4 =25 %`

Correct Answer is `=>` (B) only temperature

Q 2854467354

The mode of propagation of heat from the sun to the earth is

(A)

conduction alone

(B)

convection alone

(C)

radiation alone

(D)

Both convection and radiation

Solution:

We know that, efficiency of Carnot engine,

`eta =1 - T_2/T_1 => eta = 1 - 300/400`

[given `T_2 = 300 K, T_1 = 400 K`]

`=(400 -300)/400 = 100/400 =1/4 =25 %`

Correct Answer is `=>` (C) radiation alone

Q 2824467351

The blackboard seems black because it

(A)

reflects every colour

(B)

does not reflect any colour

(C)

absorbs black colour

(D)

reflects black colour

Solution:

We know that, efficiency of Carnot engine,

`eta =1 - T_2/T_1 => eta = 1 - 300/400`

[given `T_2 = 300 K, T_1 = 400 K`]

`=(400 -300)/400 = 100/400 =1/4 =25 %`

Correct Answer is `=>` (B) does not reflect any colour

Q 2704501458

Why is it difficult to measure the coefficient of expansion of a liquid than solid?
NDA Paper 2 2017

(A)

Liquids tend to evaporate at all temperatures

(B)

Liquids conduct more heat

(C)

Liquids expand too much when heated

(D)

Their containers also expand when heated

Solution:

We know that, efficiency of Carnot engine,

`eta =1 - T_2/T_1 => eta = 1 - 300/400`

[given `T_2 = 300 K, T_1 = 400 K`]

`=(400 -300)/400 = 100/400 =1/4 =25 %`

Correct Answer is `=>` (D) Their containers also expand when heated

Q 2306112978

Which one of the following is the mode of heat transfer in which warm material is transported so as to displace a cooler material?
NDA Paper 2 2009

(A)

Conduction only

(B)

Convection only

(C)

Radiation

(D)

Both conduction and convection

Solution:

Whenever the temperature of the lower region in a fluid (liquid or gas) becomes higher than the temperature of the upper region. The density of fluid in the lower region becomes less than that in the upper region. Hence, particles of the fluid in the lower region begin to rise and their places are occupied by the particles in the upper region. This process of heat-transmission in which the particles of the fluid move is called convection.

Correct Answer is `=>` (B) Convection only

Q 2304680558

The thermal conductivity of copper is `4` times that of brass. Two rods of copper and brass having same length and cross-section are joined end to end. The free end of copper is at `0 ^oC` and the free end of brass is at `100 ^oC`. The temperature of the junction is
NDA Paper 2 2012

(A)

`20^o C`

(B)

`40^o C`

(C)

`60^o C`

(D)

`10^o C`

Solution:

Temperature of the junction will be `20^o C`.

Correct Answer is `=>` (A) `20^o C`

Q 2324145951

A hot object loses heat to its surroundings in the form of heat radiation. The rate of loss of heat depends on the
NDA Paper 2 2012

(A)

temperature of the object

(B)

temperature of the surroundings

(C)

temperature difference between the object and its surroundings

(D)

average temperature of the object and its surroundings

Solution:

A heat object loses heat to its surroundings in the form of heat radiation. The rate of loss of heat depends on the temperature differences between the objects and its surroundings.

Correct Answer is `=>` (C) temperature difference between the object and its surroundings

Q 2188623507

The brightness of a star depends on its
NDA Paper 2 2016

(A)

size and temperature

(B)

size and distance from the Earth

(C)

size, temperature and mass

(D)

size, temperature and distance from the Earth

Solution:

According to Stefan's law, rate of loss of heat energy in the form of radiation (brightness) of a star depends upon

(i) nature of surface of radiant object

(ii) surface area of the star

(iii) temperature of the star

Correct Answer is `=>` (A) size and temperature