Thermal Equilibrium and Heat

Thermal Equilibrium and Heat MDCAT MCQs with answers

15 past paper MCQs on Thermal Equilibrium and Heat, from the Thermodynamics unit of MDCAT Physics. The year each question appeared is shown where known; tap “Show answer” for the correct option and a short solution.

Read the notes first Practise the unit as a quiz

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
Show answer

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
Show answer

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
Show answer

Correct answer: (c) High to low temperature

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

4.During rubbing of hands, internal energy: (NUMS MDCAT 2025)

  1. Increases
  2. Decreases
  3. Zero
  4. Remains same
Show answer

Correct answer: (a) Increases

Friction turns the work of rubbing into internal energy, so the hands warm.

5.During the drilling of a metal surface the drill bit heats up. This heat comes from the: (SIBA MDCAT 2025)

  1. Vibration of the tool
  2. Work done against friction
  3. Flow of electric current
  4. Compression of air
Show answer

Correct answer: (b) Work done against friction

The work done against friction is turned into internal energy, which raises the temperature of the bit.

6.When thermal energy is transferred from a hot object to a cold one, the change occurs in the hot object as: (SZABMU MDCAT 2025)

  1. Increases in internal energy
  2. Decrease in internal energy
  3. Increase in temperature
  4. Increase in heat content
Show answer

Correct answer: (b) Decrease in internal energy

The hot body gives up heat, so its internal energy falls.

7.Consider an ideal gas confined to the cylinder with a fixed piston, on heating the gas, all the heat supplied increases (KMU MDCAT 2024)

  1. Kinetic energy of the molecules
  2. Potential Energy of the molecules
  3. The intermolecular forces between gas molecules
  4. The number of gas molecules
Show answer

Correct answer: (a) Kinetic energy of the molecules

An ideal gas has no intermolecular forces, so all the heat goes into the motion of its molecules.

8.Thermodynamics is that branch of Physics in which we study (UHS MDCAT 2023)

  1. relations between heat and mechanical energies
  2. relations between heat and ionization energies
  3. relations between chemical and mechanical energies
  4. relations between kinetic and potential energies
Show answer

Correct answer: (a) relations between heat and mechanical energies

Thermodynamics is the study of heat and its relation to mechanical work.

9.A fixed mass of an ideal gas is contained in a cylinder at constant temperature. Now, the pressure of the gas is decreased. (PMC Practice 2021)

  1. Their mean square speed decreases
  2. Number of collision between molecules and walls of container decreased
  3. The force of attraction between them increase
  4. Their size decreases
Show answer

Correct answer: (b) Number of collision between molecules and walls of container decreased

At the same temperature the molecules move as fast as before; there are simply fewer collisions with the walls.

10.Which of the following is not an assumption of the kinetic model of an ideal gas? (PMC Practice 2021)

  1. The size of the molecules is much smaller than the separation between molecules
  2. Molecules suffer negligible momentum change during wall collisions
  3. Molecules do not exert force on each other except during a collision
  4. The gas molecules are in random motion and may change their direction of motion after every collision
Show answer

Correct answer: (b) Molecules suffer negligible momentum change during wall collisions

The collisions with the wall are what produce the pressure, and they are perfectly elastic but far from negligible.

11.The sum of all forms of molecular energies (Kinetic and Potential) of a substance is termed as? (UHS MDCAT 2019)

  1. Elastic energy
  2. Absolute energy
  3. Internal energy
  4. Heat energy
Show answer

Correct answer: (c) Internal energy

The sum of the kinetic and potential energies of all the molecules is the internal energy.

12.Molecules Of a gas at constant pressure for a fixed amount of gas have average kinetic energy X. Increasing temperature from 27 C to 327C, average K.E. of molecules will become: (UHS MDCAT 2019)

  1. 20X
  2. 300X
  3. 200X
  4. 2X
Show answer

Correct answer: (d) 2X

Mean kinetic energy goes as the absolute temperature, and $600/300$ is two.

13.Find the mean translational kinetic energy of ideal hydrogen gas at 17 degree Celcius. (UHS MDCAT 2018)

  1. 6.21 x 10-21J
  2. 5 x 10-21J
  3. 6.21 x 10-12J
  4. 6 x 10-21J
Show answer

Correct answer: (d) 6 x 10-21J

$\tfrac32kT=1.5\times1.38\times10^{-23}\times290$, about $6\times10^{-21}\,\mathrm{J}$.

14.The relation ‘PV = nRT’ shows which law of physics: (UHS MDCAT 2016)

  1. Charles Law
  2. Avogadro’s Law
  3. Newton’s Constant
  4. Ideal Gas Law
Show answer

Correct answer: (d) Ideal Gas Law

$PV=nRT$ is the ideal gas equation.

15.The relation R/NA = 1.38 x 10-25 JK-1 in a gas law is known as: (UHS MDCAT 2016)

  1. Avogadro’s constant
  2. Charles constant
  3. Newton’s constant
  4. Boltzmann’s constant
Show answer

Correct answer: (d) Boltzmann’s constant

The gas constant per molecule is Boltzmann’s constant.

More in Thermodynamics