Thermodynamics — DPP 1

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
Calculate the heat supplied in figure shown for complete cycle.
Thermodynamics – NEET-11454
  1. A $5 \times 10 ^ { 5 } \mathrm {~J}$
  2. B $- 5 \times 10 ^ { 5 } \mathrm {~J}$
  3. C $5 \times 10 ^ { 4 } \mathrm {~J}$
  4. D $- 5 \times 10 ^ { 4 } \mathrm {~J}$
Show answer

Correct answer: B

2
A Carnot engine absorbs an amount Q of heat from a reservoir at an absolute temperature T and rejects heat to a sink at a temperature of $\frac { T } { 3 }$. The amount of heat rejected is
  1. A $\frac { Q } { 4 }$
  2. B $\frac { Q } { 3 }$
  3. C $\frac { Q } { 2 }$
  4. D $\frac { 2 Q } { 3 }$
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Correct answer: B

3
A gas is taken through a cyclic process ABCA as shown in figure. If 2.4 cal of heat is given in the process. Calculate the value of J.
Thermodynamics – NEET-11456
  1. A 4.16 J/cal
  2. B 8.32 J/cal
  3. C 2.08 J/cal
  4. D 6.24 J/cal
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Correct answer: A

4
Three samples of the same gas A, B, and C (γ = 3/2) have equal volumes initially. Now, the volume of each sample is doubled. For A, the process is adiabatic; for B, it is isobaric, and for C, the process is isothermal. If the final pressures are equal for all three samples, the ratio of their initial pressure is:
  1. A $2 : 1 : \sqrt { 2 }$
  2. B $2 \sqrt { 2 } : 1 : 2$
  3. C $\sqrt { 2 } : 1 : 2$
  4. D $\sqrt { 2 } : 2 : 1$
Show answer & explanation

Correct answer: B

Thermodynamics – NEET-11471 Therefore, option (B) is the correct answer.
5
A Carnot engine takes $6 \times 10 ^ { 6 } \mathrm { cal }$ of heat from reservoir at $627 ^ { \circ } \mathrm { C }$ and gives it to a sink at $27 ^ { \circ } \mathrm { C }$. Then work done by the engine is:
  1. A $4.2 \times 10 ^ { 6 } \mathrm {~J}$
  2. B $8.4 \times 10 ^ { 6 } \mathrm {~J}$
  3. C $16.8 \times 10 ^ { 6 } \mathrm {~J}$
  4. D zero
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Correct answer: A

6
The P-V diagram of 2 g of Helium gas for a certain process A → B is shown in figure. Heat given to the body during process A → B is:
Thermodynamics – NEET-11461
  1. A $4 P _ { 0 } V _ { 0 }$
  2. B $12 \mathrm { P } _ { 0 } \mathrm {~V} _ { 0 }$
  3. C $6 P _ { 0 } V _ { 0 }$
  4. D $15 \mathrm { P } _ { 0 } \mathrm {~V} _ { 0 }$
Show answer

Correct answer: D

7
A monoatomic gas at a pressure P , having a volume V expands isothermally to a volume 2 V and then adiabatically to a volume 16 V. What is the final pressure of the gas? (take, γ = $\frac{5}{3}$)
  1. A 64 P
  2. B 32 P
  3. C $\frac { \mathrm { P } } { 64 }$
  4. D 16 P
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Correct answer: C

8
In an adiabatic change, the pressure and temperature of a monoatomic gas are related with relation p ∝ T$^{n}$, where n is equal to:
  1. A $\frac { 5 } { 4 }$
  2. B $\frac { 5 } { 3 }$
  3. C $\frac { 5 } { 2 }$
  4. D $\frac { 3 } { 5 }$
Show answer

Correct answer: C

9
A perfect gas is found to obey the relation $\mathrm { pV } ^ { 3 / 2 } =$ constant, during an adiabatic process, if such a gas initially at a temperature T , is compressed to half of its initial volume, what is the final temperature.
  1. A 2T
  2. B 4T
  3. C $(2)^{1 / 2} \mathrm{~T}$
  4. D $2(2)^{1 / 2} \mathrm{~T}$
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Correct answer: C

10
A perfect gas goes from state A to state B by absorbing $8 \times 10 ^ { 5 } \mathrm {~J}$ of heat and doing $6.5 \times 10 ^ { 5 } \mathrm {~J}$ of external work. It is now transferred between the same two states in another process in which it absorbs $10 ^ { 5 } \mathrm {~J}$ of heat. In the second process:
  1. A Work done on gas is $10 ^ { 5 } \mathrm {~J}$
  2. B Work done on gas is $0.5 \times 10 ^ { 5 } \mathrm {~J}$
  3. C Work done by gas is $10 ^ { 5 } \mathrm {~J}$
  4. D Work done by gas is $0.5 \times 10 ^ { 5 } \mathrm {~J}$
Show answer & explanation

Correct answer: B

Sign convention we will use
Work done by the system → +ve
Work done on the system → –ve
Heat absorbed by the system → +ve
Heat given by the system → –ve
dQ = dU + dW
dU = 8 × 10$^{5}$ – 6.5 × 10$^{5}$
dU = 1.5 × 10$^{5}$ J
In second case internal energy will be the same
dQ = dU + dW
dW = 10$^{5}$ – 1.5 × 10$^{5}$
Work is done on the system
dW = –0.5 × 10$^{5}$ J
Magnitude of this work done is 0.5 × 10$^{5}$ J.
Therefore, option (B) is the correct answer.
11
A gas is expanded from volume V to 2V under three different processes, as shown in the figure. Process 1 is isobaric process, 2 is isothermal and process 3 is adiabatic. Let $\Delta \mathrm { U } _ { 1 }$, $\Delta \mathrm { U } _ { 2 }$ and $\Delta \mathrm { U } _ { 3 }$ be the range of internal energy of the gas in these three processes, then:
Thermodynamics – NEET-11466
  1. A $\Delta \mathrm { U } _ { 1 } > \Delta \mathrm { U } _ { 2 } > \Delta \mathrm { U } _ { 3 }$
  2. B $\Delta \mathrm { U } _ { 1 } < \Delta \mathrm { U } _ { 2 } < \Delta \mathrm { U } _ { 3 }$
  3. C $\Delta \mathrm { U } _ { 2 } > \Delta \mathrm { U } _ { 1 } > \Delta \mathrm { U } _ { 3 }$
  4. D $\Delta \mathrm { U } _ { 2 } > \Delta \mathrm { U } _ { 3 } > \Delta \mathrm { U } _ { 1 }$
Show answer & explanation

Correct answer: A

Thermodynamics – NEET-11466 Thermodynamics – NEET-11466 Therefore, option (A) is the correct answer.
12
A Carnot's engine used first an ideal monoatomic gas then an ideal diatomic gas. If the source and sink temperature are $411 ^ { \circ } \mathrm { C }$ and $69 ^ { \circ } \mathrm { C }$ respectively and the engine extracts 1000 J of heat in each cycle, then area enclosed by the PV diagram is:
  1. A 100 J
  2. B 300 J
  3. C 500 J
  4. D 700 J
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Correct answer: C

13
P-V plots for two gases during adiabatic processes are shown in the figure. Plots 1 and 2 should correspond respectively to:
Thermodynamics – NEET-11475
  1. A He and O₂
  2. B O₂ and He
  3. C He and Ar
  4. D O₂ and N₂
Show answer & explanation

Correct answer: B

Thermodynamics – NEET-11475 Therefore, option (B) is the correct answer.
14
At 8 atm pressure a monoatomic gas expands from 2 litre to 5 litre then calculate the amount of work done by gas.
  1. A 2400 J
  2. B 3600 J
  3. C 6000 J
  4. D 7400 J
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Correct answer: A

15
When one mole of a mono-atomic gas expands at constant pressure, the ratio of the heat supplied that increases the internal energy of the gas and that is used in expansion is:
  1. A ∞
  2. B Zero
  3. C $\frac { 3 } { 2 }$
  4. D $\frac { 2 } { 3 }$
Show answer & explanation

Correct answer: C

Thermodynamics – NEET-11470
16
If 4 moles of a monoatomic gas and 2 moles of a diatomic gas are mixed then find value of γ for the mixture.
  1. A 1.54
  2. B 1.4
  3. C 1.67
  4. D 1.2
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Correct answer: A

17
A gas is heated at constant pressure. The fraction of heat supplied used for to external work is:
  1. A $\frac { 1 } { \gamma }$
  2. B $\left( 1 - \frac { 1 } { \gamma } \right)$
  3. C $\gamma - 1$
  4. D $\left( 1 - \frac { 1 } { \gamma ^ { 2 } } \right)$
Show answer & explanation

Correct answer: B

Heat given to isobaric process
Thermodynamics – NEET-11467 Therefore, option (B) is the correct answer.
18
Two containers of equal volumes contain the same gas at pressures P$_{1}$ and P$_{2}$ and absolute temperatures T$_{1}$ and T$_{2}$ respectively. On joining the vessels, the gas reaches a common pressure p and a common temperature T. The ratio P/T is equal to:
  1. A $\frac { \mathrm { P } _ { 1 } } { \mathrm {~T} _ { 1 } } + \frac { \mathrm { P } _ { 2 } } { \mathrm {~T} _ { 2 } }$
  2. B $\frac { 1 } { 2 } \left[ \frac { \mathrm { P } _ { 1 } } { \mathrm {~T} _ { 1 } } + \frac { \mathrm { P } _ { 2 } } { \mathrm {~T} _ { 2 } } \right]$
  3. C $\frac { P _ { 1 } T _ { 2 } + P _ { 2 } T _ { 1 } } { T _ { 1 } + T _ { 2 } }$
  4. D $\frac { P _ { 1 } T _ { 2 } - P _ { 2 } T _ { 1 } } { T _ { 1 } - T _ { 2 } }$
Show answer & explanation

Correct answer: B

For a closed system, the total mass of gas or the number of moles remains constant.
Thermodynamics – NEET-11465 Therefore, option (B) is the correct answer.
19
Two gases kept in two identical vessels of volume 30 litres at same temperature 300 K and same pressure 20 atm are mixed isothermally in vessel having same volume. What will be the resulting pressure of the mixture?
  1. A 40 atm
  2. B 20 atm
  3. C 80 atm
  4. D 100 atm
Show answer

Correct answer: A

20
An ideal mono-atomic gas is taken around the cycle ABCDA as shown in the P-V diagram:
Thermodynamics – NEET-11468 The work done during the cycle is:
  1. A PV
  2. B 2PV
  3. C PV/2
  4. D Zero
Show answer & explanation

Correct answer: A

Work done will be given by area under the P–V graph.
Area = (2P – P) × (2V – V) = PV
Therefore, option (A) is the correct answer.

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