Thermodynamics

Thermodynamics MDCAT MCQs with answers

72 past paper MCQs from Physics unit 7, Thermodynamics, across 5 topics. They are arranged topic by topic; bigger topics show a sample here and link to their full set and to study notes. Tap “Show answer” for the correct option and a short solution.

Practise as a quiz

Thermal Equilibrium and Heat

1.Thermodynamics is that branch of physics in which we study the: (MDCAT 2022)

  1. relations between heat and mechanical energies
  2. relations between heat and internal energies only
  3. relations between chemical and mechanical energies
  4. relations between kinetic and potential energies
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Correct answer: (a) relations between heat and mechanical energies

Thermodynamics is about the exchange between thermal energy and mechanical work.

2.The pressure of a gas is directly proportional to the: (UHS MDCAT 2017)

  1. average kinetic energy of its molecules
  2. average vibrational kinetic energy of its molecules
  3. average translational kinetic energy of its molecules
  4. all of the above
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Correct answer: (c) average translational kinetic energy of its molecules

The pressure comes from molecules striking the walls, so it is the translational part of the kinetic energy that counts.

3.Heat will spontaneously flow from: (KMU MDCAT 2025)

  1. Lower to higher internal energy only
  2. High pressure to low pressure
  3. High to low temperature
  4. Low temperature to high temperature
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Correct answer: (c) High to low temperature

Heat of itself passes only from the hotter body to the colder one.

All 15 Thermal Equilibrium and Heat MCQs → Thermal Equilibrium and Heat notes →

Work Done by a Thermodynamic System

4.The temperature of a given mass of a gas is changed from $150^\circ$C to $300^\circ$C during an isobaric process. The volume of the gas will become: (MDCAT 2022)

  1. half
  2. double
  3. the same
  4. less than double
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Correct answer: (d) less than double

Volume goes as the absolute temperature, and $573/423\approx1.35$, which is less than twice.

5.Bursting of tire is an example of which process? (NUMS MDCAT 2025)

  1. Adiabatic
  2. Isochoric
  3. Isothermal
  4. Isobaric
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Correct answer: (a) Adiabatic

The air escapes too fast for any heat to be exchanged, so the expansion is adiabatic.

6.A gas expands from 1 m^3 to 3 m^3 at constant pressure of 2 Pa. Work done is: (SIBA MDCAT 2025)

  1. 2J
  2. 4J
  3. 6J
  4. 8J
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Correct answer: (b) 4J

$W=P\Delta V=2\times2$, which is $4\,\mathrm{J}$.

All 16 Work Done by a Thermodynamic System MCQs → Work Done by a Thermodynamic System notes →

First Law of Thermodynamics

7.The rapid escape of air from a burst tyre is an example of a process that is: (MDCAT 2020)

  1. isothermal
  2. adiabatic
  3. isobaric
  4. isochoric
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Correct answer: (b) adiabatic

The escape is too quick for any heat exchange, so $Q=0$ and the air cools as it does work.

8.When a gas expands isothermally, the product of its pressure and volume during the process is: (MDCAT 2022)

  1. not constant
  2. constant
  3. zero
  4. proportional to entropy
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Correct answer: (b) constant

At constant temperature $PV=nRT$ is fixed, which is Boyle's law.

9.The first law of thermodynamics concerns the conservation of: (MDCAT 2023)

  1. heat
  2. work
  3. momentum
  4. energy
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Correct answer: (d) energy

$\Delta U=Q-W$ is the conservation of energy written for a thermodynamic system.

All 20 First Law of Thermodynamics MCQs → First Law of Thermodynamics notes →

Specific Heat and Molar Specific Heat of a Gas

10.Which of the following has highest specific heat capacity? (NUMS MDCAT 2025)

  1. Copper
  2. Iron
  3. Water
  4. Glass
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Correct answer: (c) Water

Water has an unusually high specific heat, about $4200\,\mathrm{J\,kg^{-1}\,K^{-1}}$.

11.The specific heat of a gas in adiabatic process is: (PMC MDCAT 2022)

  1. Zero
  2. Infinite
  3. Negative
  4. Remains constant
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Correct answer: (a) Zero

No heat is exchanged in an adiabatic change, so the heat per degree is zero.

12.Molar heat capacity at constant pressure is given by: (PMC MDCAT 2022)

  1. dQ/dV
  2. dQ/dT
  3. dU/dT
  4. dU/dV
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Correct answer: (b) dQ/dT

Molar heat capacity is the heat needed per mole for each degree of temperature rise.

All 11 Specific Heat and Molar Specific Heat of a Gas MCQs → Specific Heat and Molar Specific Heat of a Gas notes →

Relation Between Cp and Cv

13.An ideal gas has molar specific heat $C_p$ at constant pressure. When the temperature of $n$ moles is increased by $\Delta T$, the increase in the internal energy is: (MDCAT 2023)

  1. $nC_p\Delta T$
  2. $n(C_p+R)\Delta T$
  3. $n(C_p-R)\Delta T$
  4. $n(2C_p+R)\Delta T$
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Correct answer: (c) $n(C_p-R)\Delta T$

$\Delta U=nC_v\Delta T$ and $C_p-C_v=R$, so $C_v=C_p-R$.

14.At a constant Pressure (Cp) and Volume (Cv), an ideal gas has C p - C v = R Then Cp will be? (KMU MDCAT 2025)

  1. R/2
  2. 3/2 R
  3. 5/2 R
  4. 7/2 R
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Correct answer: (c) 5/2 R

For a monatomic ideal gas $C_v=\tfrac32R$, so $C_p=C_v+R=\tfrac52R$.

15.For a monatomic ideal gas of 3 mole, Cp -Cv is: (PMC MDCAT 2022)

  1. R/3
  2. 3/2 R
  3. 2R
  4. 3R
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Correct answer: (d) 3R

$C_p-C_v=R$ for each mole, so for three moles it is $3R$.

All 10 Relation Between Cp and Cv MCQs → Relation Between Cp and Cv notes →

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