Thermodynamics — DPP 2

20 NEET questions from Thermodynamics, with answers and explanations. Attempt it as a timed test to get scoring, accuracy breakdown and mistake tracking.

Attempt this test free 20 questions · 30 minutes · +80 marks
1
When a system is taken from state 1 to 2 along the path 1a2 it absorbs 50 cal of heat and work done is 20 cal. Along the path 1b2, Q = 36 cal. What is the work done along 1b2?
Thermodynamics – NEET-11498
  1. A 56 cal
  2. B 66 cal
  3. C 16 cal
  4. D 6 cal
Show answer

Correct answer: D

2
A system is provided with 200 cal of heat, and the work done by the system on the surroundings is 40 J. Then its internal energy
  1. A Increases by 600 J
  2. B Decreases by 800 J
  3. C Increases by 800 J
  4. D Decreases by 50 J
Show answer

Correct answer: C

3
Consider the process of a system shown in figure, during the process work done by gas is:
Thermodynamics – NEET-11469
  1. A Continuously increasing
  2. B Continuously decreasing and becomes zero at t = ∞
  3. C First decreasing then increasing
  4. D None of the above
Show answer & explanation

Correct answer: A

∵ Area under the P–V curve is continuously increasing as time passes, so during the process, work done by the gas is continuously increasing.
Therefore, option (A) is the correct answer.
4
For an adiabatic expansion of an ideal gas the fractional change in its pressure is equal to
  1. A $- \gamma \frac { V } { d V }$
  2. B $- \frac { d V } { \gamma V }$
  3. C $\frac { d V } { V }$
  4. D $- \gamma \frac { d V } { V }$
Show answer

Correct answer: D

5
In adiabatic expansion of a gas
  1. A its pressure increases
  2. B its temperature falls
  3. C its density increases
  4. D its thermal energy increases
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Correct answer: B

6
In a thermodynamic process, pressure of a fixed mass of a gas is changed in such a manner that the gas molecules gives out 20 J of heat and 10 J of work is done on the gas. If the initial internal energy of the gas was 40 J, then the final internal energy will be
  1. A 30 J
  2. B 20 J
  3. C 60 J
  4. D 40 J
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Correct answer: A

7
Select the incorrect relation. (Where symbols have their usual meanings)
  1. A $C _ { P } = \frac { \gamma R } { \gamma - 1 }$
  2. B $C _ { P } - C _ { V } = R$
  3. C $\Delta U = \frac { P _ { f } V _ { f } - P _ { i } V _ { i } } { 1 - \gamma }$
  4. D $C _ { V } = \frac { R } { \gamma - 1 }$
Show answer

Correct answer: C

8
If the temperature of the source is increased, the efficiency of a carnot engine:
  1. A Increases
  2. B Decreases
  3. C Remains constant
  4. D First increases and then remains constant
Show answer & explanation

Correct answer: A

Increases
$\eta=1-\frac{\mathrm{T}_{2}}{\mathrm{~T}_{1}}$, T$_{1}$ increased
Efficiency η → increases
Therefore, option (A) is the correct answer.
9
Even Carnot engine cannot give 100% efficiency because we cannot
  1. A prevent radiation
  2. B find ideal sources
  3. C reach absolute zero temperature
  4. D eliminate friction
Show answer

Correct answer: C

10
If 150 J of heat is added to a system and the work done by the system is 110 J, then change in internal energy will be
  1. A 260 J
  2. B 150 J
  3. C 110 J
  4. D 40 J
Show answer

Correct answer: D

11
50 calories of heat is needed to raise the temperature of 1 mol of an ideal monoatomic gas from $20 ^ { \circ } \mathrm { C }$ to $30 ^ { \circ } \mathrm { C }$ at a constant pressure. The amount of heat required to raise its temperature over the same interval at a constant volume ( $R = 2$ calmol $^ { - 1 } \mathrm {~K} ^ { - 1 }$ ) is
  1. A 30 cal
  2. B 40 cal
  3. C 60 cal
  4. D 80 cal
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Correct answer: A

12
For a cyclic process
  1. A ΔU = 0
  2. B ΔQ = 0
  3. C W = 0
  4. D Both (A) & (C)
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Correct answer: A

13
In an adiabatic change the pressure and temperature of a monoatomic gas are related with relation $\mathrm { P } \propto T ^ { C }$, where C is equal to
  1. A $\frac { 3 } { 2 }$
  2. B $\frac { 5 } { 2 }$
  3. C $\frac { 7 } { 9 }$
  4. D $\frac { 9 } { 7 }$
Show answer

Correct answer: B

14
In thermodynamic process, 200 joules of heat is given to a gas and 100 joules of work is also done on it. The change in internal energy of the gas is
  1. A 100 J
  2. B 300 J
  3. C 419 J
  4. D 24 J
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Correct answer: B

15
Assertion (A): During a cyclic process work done by the system is zero.
Reason (R): Heat supplied to a system in the cyclic process converts into internal energy of the system.
  1. A Both Assertion (A) and Reason (R) are True and the Reason (R) is a correct explanation of the Assertion (A).
  2. B Both Assertion (A) and Reason (R) are True but Reason (R) is not a correct explanation of the Assertion (A).
  3. C Assertion (A) is True but the Reason (R) is False.
  4. D Assertion (A) and Reason (R) are False
Show answer

Correct answer: D

16
1 mole of a gas with $\gamma = \frac { 7 } { 5 }$ is mixed with 1 mole of another gas having $\gamma = \frac { 5 } { 3 }$, the value of $\gamma$ of the resulting mixture is:
  1. A $\frac { 7 } { 5 }$
  2. B $\frac { 2 } { 5 }$
  3. C $\frac { 3 } { 2 }$
  4. D $\frac { 12 } { 7 }$
Show answer & explanation

Correct answer: C

$\because \frac{\mathrm{n}_{1}+\mathrm{n}_{2}}{\gamma-1}=\frac{\mathrm{n}_{1}}{\gamma_{1}-1}+\frac{\mathrm{n}_{2}}{\gamma_{2}-1}$
$\begin{array}{l}\Rightarrow \frac{2}{\gamma-1}=\frac{1}{\frac{7}{5}-1}+\frac{1}{\frac{5}{3}-1} \\ \Rightarrow \gamma=3 / 2\end{array}$
Therefore, option (C) is the correct answer.
17
The P-V diagram of path followed by one mole of a perfect gas in a cylindrical container is shown in figure, the work done when the gas is taken from state A to state B is:
Thermodynamics – NEET-11472
  1. A $2 P_{2} V_{1}\left[1-\frac{\sqrt{V_{2}}}{\sqrt{V_{1}}}\right]$
  2. B $2 P_{1} V_{1}\left[1-\frac{\sqrt{V_{1}}}{\sqrt{V_{2}}}\right]$
  3. C $2 \mathrm{P}_{1} \mathrm{~V}_{2}\left[\frac{\sqrt{\mathrm{~V}_{1}}}{\sqrt{\mathrm{~V}_{2}}}-1\right]$
  4. D $2 P_{2} V_{2}\left[1-\frac{\sqrt{V_{1}}}{\sqrt{V_{2}}}\right]$
Show answer & explanation

Correct answer: B

Thermodynamics – NEET-11472 Therefore, option (B) is the correct answer.
18
If the door of a refrigerator is kept open, which of the following is true?
  1. A Room is cooled
  2. B Room is heated
  3. C Room is either cooled or heated
  4. D Room is neither cooled nor heated
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Correct answer: B

19
Assertion (A): Internal energy of ideal gas does not depend upon the volume of the gas
Reason (R): This is because internal energy of ideal gas depends on temperature of gas.
  1. A Both Assertion (A) and Reason (R) are True and the Reason (R) is a correct explanation of the Assertion (A).
  2. B Both Assertion (A) and Reason (R) are True but Reason (R) is not a correct explanation of the Assertion (A).
  3. C Assertion (A) is True but the Reason (R) is False.
  4. D Assertion (A) and Reason (R) are False
Show answer

Correct answer: A

20
A gas undergoes a process in which its pressure P and volume V are related as VP$^{n}$ = constant. The bulk modulus for the gas in this process is:
  1. A $n P$
  2. B $P ^ { \frac { 1 } { n } }$
  3. C $\frac { P } { n }$
  4. D $P ^ { n }$
Show answer & explanation

Correct answer: C

Thermodynamics – NEET-11474 Therefore, option (C) is the correct answer.

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