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Explore popular questions from Thermodynamics for NEET. This collection covers Thermodynamics previous year NEET questions hand picked by experienced teachers.

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Thermodynamics

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Q 1. Equal volumes of two monatomic gases, {tex} A {/tex} and {tex} B {/tex} at same temperature and pressure are mixed. The ratio of specific heats {tex} \left( C _ { P } / C _ { V } \right) {/tex} of the mixture will be

A

0.83

B

1.50

C

3.3

1.67

Explanation

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Q 2. The relation between {tex} U , P {/tex} and {tex} V {/tex} for an ideal gas in an adiabatic process is given by relation {tex} U = a + b P V . {/tex} Find the value of adiabatic exponent {tex} ( \gamma ) {/tex} of this gas

{tex} \frac { b + 1 } { b } {/tex}

B

{tex} \frac { b + 1 } { a } {/tex}

C

{tex} \frac { a + 1 } { b } {/tex}

D

{tex} \frac { a } { a + b } {/tex}

Explanation

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Q 3. Carbon monoxide is carried around a closed cycle abc in which bc is an isothermal process as shown in the figure. The gas absorbs 7000{tex} \mathrm { J } {/tex} of heat as its temperture increases from 300{tex} \mathrm { K } {/tex} to 1000{tex} \mathrm { K } {/tex} in going from a to b. The quantity of heat rejected by the gas during the process ca is

A

4200{tex} \mathrm { J } {/tex}

B

{tex} 5000 \mathrm J {/tex}

C

9000{tex} \mathrm { J } {/tex}

9800{tex} \mathrm { J } {/tex}

Explanation

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Q 4. A Carnot engine, having an efficiency of {tex} \eta = 1 / 10 {/tex} as heat engine, is used as a refrigerator. If the work done on the system is 10{tex} \mathrm { J } {/tex} , the amount of energy absorbed from the reservoir at lower temperature is

A

100{tex} \mathrm { J } {/tex}

B

99{tex} \mathrm { J } {/tex}

90{tex} \mathrm { J } {/tex}

D

1{tex} \mathrm { J } {/tex}

Explanation

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Q 5. In a thermodynamic process, fixed mass of a gas is changed in such a manner that the gas release 20{tex} \mathrm { J } {/tex} of heat and 8{tex} \mathrm { J } {/tex} of work was done on the gas. If the initial internal energy of the gas was 30{tex} \mathrm { J } {/tex} . Then the final internal energy will be

A

2 joule

18 joule

C

42 joule

D

58 joule

Explanation

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Q 6. A closed gas cylinder is divided into two parts by a piston held tight. The pressure and volume of gas in two parts respectively are {tex} ( \mathrm { P } , 5 \mathrm { V } ) {/tex} and {tex} ( 10 \mathrm { P } , \mathrm { V } ) {/tex} . If now the piston is left free and the system undergoes isothermal process, then the volumes of the gas in two parts respectively are

{tex} 2 \mathrm { V } , 4 \mathrm { V } {/tex}

B

{tex} 3 \mathrm { V } , 3 \mathrm { V } {/tex}

C

{tex} 5 \mathrm { V } , \mathrm { V } {/tex}

D

{tex} \frac { 10 } { 11 } \mathrm { V } , \frac { 20 } { 11 } \mathrm { V } {/tex}

Explanation

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Q 7. The efficiency of an ideal gas with adiabatic exponent {tex} '\gamma' {/tex} for the shown cyclic process would be

{tex} \frac { ( 2 \ln 2 - 1 ) } { \gamma / ( \gamma - 1 ) } {/tex}

B

{tex} \frac { ( 1 - 2 \ln 2 ) } { \gamma / ( \gamma - 1 ) } {/tex}

C

{tex} \frac { ( 2 \ln 2 + 1 ) } { \gamma / ( \gamma - 1 ) } {/tex}

D

{tex} \frac { ( 2 \ln 2 - 1 ) } { \gamma / ( \gamma + 1 ) } {/tex}

Explanation

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Q 8. A mass of diatomic gas {tex} ( \gamma = 1.4 ) {/tex} at a pressure of 2 atmospheres is compressed adiabatically so that its temperature rises from {tex} 27 ^ { \circ } \mathrm { C } {/tex} to {tex} 927 ^ { \circ } \mathrm { C } {/tex} . The pressure of the gas in final state is

A

28{tex} \mathrm { atm } {/tex}

B

68.7{tex} \mathrm { atm } {/tex}

256{tex} \mathrm { atm } {/tex}

D

8{tex} \mathrm { atm } {/tex}

Explanation

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Q 9. A diatomic ideal gas is used in a Carnot engine as the working substance. If during the adiabatic expansion part of the cycle the volume of the gas increases from {tex} V {/tex} to 32{tex} V {/tex} , the efficiency of the engine is

A

0.5

0.75

C

0.99

D

0.25

Explanation

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Q 10. The P -V diagram of a gas system undergoing cyclic process is shown here. The work done during isobaric compression is

A

100{tex} \mathrm { J } {/tex}

B

200{tex} \mathrm { J } {/tex}

C

600{tex} \mathrm { J } {/tex}

400{tex} \mathrm J {/tex}

Explanation

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Q 11. During an adiabatic process of an ideal gas, if {tex} \mathrm { P } {/tex} is proportional to {tex} \frac { 1 } { \mathrm { V } ^ { 1.5 } } {/tex} , then the ratio of specific heat capacities at constant pressure to that at constant volume for the gas is

1.5

B

0.25

C

0.75

D

0.4

Explanation

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Q 12. The work of 146{tex} \mathrm { kJ } {/tex} is performed in order to compress one kilo mole of gas adiabatically and in this process the temperature of the gas increases by {tex} 7 ^ { \circ } \mathrm { C } {/tex} . The gas is {tex} \left( R = 8.3 \mathrm { Jmol } ^ { - 1 } \mathrm { K } ^ { - 1 } \right) {/tex}

diatomic

B

triatomic

C

a mixture of monoatomic and diatomic

D

monoatomic

Explanation

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Q 13. The specific heat capacity of a metal at low temperature(T) is given as C(kJK{tex}^{-1}{/tex}kg{tex}^{-1}{/tex}) = 32{tex} ({\frac {T}{400}})^3{/tex} . A 100 g vessel of this metal is to be cooled from 20 K to 4 K by a special refrigerator operating at room temperature (27{tex} ^\circ {/tex}C). The amount of work required to cool in vessel is

A

equal to 0.002{tex} \mathrm { kJ } {/tex}

B

greater than 0.148{tex} \mathrm { kJ } {/tex}

between 0.028 {tex} \mathrm { kJ } {/tex} and 0.148{tex} \mathrm { kJ } {/tex}

D

less than 0.028{tex} \mathrm { kJ } {/tex}

Explanation

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Q 14. 5.6 litre of helium gas at STP is adiabatically compressed to 0.7 litre. Taking the initial temperature to be {tex} \mathrm { T } _ { 1 } , {/tex} the work done in the process is

{tex} \frac { 9 } { 8 } R T _ { 1 } {/tex}

B

{tex} \frac { 3 } { 2 } R T _ { 1 } {/tex}

C

{tex} \frac { 15 } { 8 } R T _ { 1 } {/tex}

D

{tex} \frac { 9 } { 2 } R T _ { 1 } {/tex}

Explanation

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Q 15. Four curves {tex} \mathrm { A } , \mathrm { B } , \mathrm { C } {/tex} and {tex} \mathrm { D } {/tex} are drawn in the figure for a given amount of a gas. The curves which represent adiabatic and isothermal changes are

A

C and D respectively

B

D and C respectively

A and B respectively

D

B and A respectively

Explanation

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Q 16. In an adiabatic process, the pressure is increased by {tex} \frac { 2 } { 3 } \% {/tex}. If {tex} \gamma = \frac { 3 } { 2 } , {/tex} then the volume decreases by nearly

{tex} \frac { 4 } { 9 } \% {/tex}

B

{tex} \frac { 2 } { 3 } \% {/tex}

C

1{tex} \% {/tex}

D

{tex} \frac { 9 } { 4 } \% {/tex}

Explanation

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Q 17. A reversible engine converts one-sixth of the heat input into work. When the temperature of the sink is reduced by {tex} 62 ^ { \circ } \mathrm { C } , {/tex} the efficiency of the engine is doubled. The temperatures of the source and sink are

{tex} 99 ^ { \circ } \mathrm { C } , 37 ^ { \circ } \mathrm { C } {/tex}

B

{tex} 80 ^ { \circ } \mathrm { C } , 37 ^ { \circ } \mathrm { C } {/tex}

C

{tex} 95 ^ { \circ } \mathrm { C } , 37 ^ { \circ } \mathrm { C } {/tex}

D

{tex} 90 ^ { \circ } \mathrm { C } , 37 ^ { \circ } \mathrm { C } {/tex}

Explanation

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Q 18. When the state of a gas adiabatically changed from an equilibrium state A to another equilibrium state B an amount of work done on the system is 35{tex} \mathrm { J } {/tex} . If the gas is taken from state {tex} \mathrm { A } {/tex} to {tex} \mathrm { B } {/tex} via process in which the net heat absorbed by the system is 12{tex} \mathrm { cal } {/tex} , then the net work done by the system is {tex} ( 1 \mathrm { cal } = 4.19 \mathrm { J } ) {/tex}

A

13.2{tex} \mathrm { J } {/tex}

15.4{tex} \mathrm { J } {/tex}

C

12.6{tex} \mathrm { J } {/tex}

D

16.8{tex} \mathrm { J } {/tex}

Explanation

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Q 19. Calculate the work done when 1 mole of a perfect gas is compressed adiabatically. The initial pressure and volume of the gas are 10{tex} ^ { 5 }{/tex} N/m{tex}^ { 2 }{/tex} and 6 litre respectively. The final volume of the gas is 2 litres. Molar specific heat of the gas at constant volume is 3R/2. [Given (3){tex}^{5/3 }{/tex} = 6.19]

{tex} - 957 \mathrm { J } {/tex}

B

{tex} + 957 \mathrm { J } {/tex}

C

{tex} - 805 \mathrm J {/tex}

D

{tex} + 805 \mathrm { J } {/tex}

Explanation

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Q 20. A Carnot engine whose efficiency is 40% , receives heat at 500{tex} \mathrm { K } {/tex} . If the efficiency is to be 50{tex} \% {/tex} , the source temperature for the same exhaust temperature is

A

900{tex} \mathrm { K } {/tex}

600{tex} \mathrm { K } {/tex}

C

700{tex} \mathrm { K } {/tex}

D

800{tex} \mathrm { K } {/tex}

Explanation

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Q 21. In a thermodynamic process, fixed mass of a gas is changed in such a manner that the gas release 20{tex} \mathrm { J } {/tex} of heat and 8{tex} \mathrm { J } {/tex} of work was done on the gas. If the initial internal energy of the gas was 30{tex} \mathrm { J } {/tex} , the final internal energy will be

A

2 joule

18 joule

C

42 joule

D

58 joule

Explanation

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Q 22. One mole of a diatomic ideal gas undergoes a cyclic process ABC as shown in figure. The process BC is adiabatic. The temperatures at A, B and C are 400 K, 800 K and 600 K respectively. Choose the correct statement:

A

The change in internal energy in whole cyclic process is 250 R

B

The change in internal energy in the process {tex} C A {/tex} is 700 R.

C

The change in internal energy in the process {tex} A B {/tex} is -350 R.

The change in internal energy in the process {tex} B C {/tex} is -500 R.

Explanation

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Q 23. In {tex} P - V {/tex} diagram shown in figure {tex} A B C {/tex} is a semicircle. The work done in the process {tex} A B C {/tex} is

A

4{tex} \mathrm { J } {/tex}

B

{tex} \frac { - \pi } { 2 } \mathrm { J } {/tex}

{tex} \frac { \pi } { 2 } \mathrm { J } {/tex}

D

Zero