Free Thermodynamics MCQs with Answers

• A. they have the same mass
• B. they are at the same temperature, so there is no net flow of heat between them
• C. they contain the same amount of heat
• D. they are made of the same material

Explanation: Temperature is what decides the direction of heat flow, so equal temperatures mean no net transfer even if the two bodies hold very…

• A. the total energy contained in a body
• B. the temperature of a body
• C. energy in transit from a hotter body to a cooler one because of the temperature difference
• D. a fluid that flows between bodies

Explanation: Heat is a process word: it names energy while it is being transferred, which is why a body is said to contain internal energy rather than…

• A. the work done by the system alone
• B. the increase in internal energy plus the work done by the system
• C. the fall in internal energy
• D. the temperature rise multiplied by the mass

Explanation: The law is conservation of energy applied to heat: energy entering as heat either raises the internal energy or leaves again as work done…

• A. the internal energy falls
• B. no heat is exchanged
• C. the temperature and therefore the internal energy stay constant, so the heat supplied equals the work done
• D. the work done is zero

Explanation: Constant temperature means constant internal energy for an ideal gas, so by the first law every joule of heat entering leaves again as…

• A. the temperature of the gas rises because work is done on it with no heat escaping
• B. the temperature falls
• C. the temperature stays constant
• D. heat flows into the gas from outside

Explanation: With no heat exchange, the work done on the gas must all go into internal energy, so the temperature rises, which is why a bicycle pump…

• A. the gas is hotter at constant pressure
• B. at constant pressure the gas also does work expanding against the surroundings
• C. the molecules move faster at constant pressure
• D. Cv is measured at a lower temperature

Explanation: At constant volume all the heat supplied raises the internal energy, but at constant pressure some of it is spent doing work as the gas…

• A. Cp minus Cv equals R
• B. Cp plus Cv equals R
• C. Cp times Cv equals R
• D. Cp equals Cv

Explanation: Mayer's relation follows directly from the first law applied to a constant pressure heating, where the extra heat needed is the work of…

• A. energy can be created in a heat engine
• B. no heat engine can convert all the heat it takes in into work
• C. heat always flows from cold to hot on its own
• D. entropy always decreases

Explanation: Some heat must always be rejected to a cold reservoir, so efficiency is necessarily less than 100 per cent however well the engine is…

• A. 20 per cent
• B. 50 per cent
• C. 75 per cent
• D. 100 per cent

Explanation: Carnot efficiency is 1 minus the ratio of the cold to the hot absolute temperature, which is 1 minus 300 over 600, giving 0.5 or 50 per…

• A. 0 degrees Celsius
• B. minus 100 degrees Celsius
• C. minus 273 degrees Celsius
• D. minus 373 degrees Celsius

Explanation: Zero kelvin is minus 273.15 degrees Celsius, the temperature at which the pressure of an ideal gas would extrapolate to zero and molecular…

• A. mass times specific heat capacity times temperature change
• B. mass divided by specific heat capacity
• C. specific heat capacity times temperature change only
• D. mass times temperature change only

Explanation: The formula Q equals mc times delta T holds whenever there is no change of state, and specific heat capacity is the heat needed to raise…

• A. raises its temperature steadily
• B. breaks the bonds of the solid structure without changing the temperature
• C. is lost to the surroundings entirely
• D. lowers the internal energy

Explanation: The latent heat of fusion goes entirely into overcoming the forces holding the lattice, so the temperature stays at the melting point…

• A. the average speed of its molecules
• B. the average kinetic energy of its molecules
• C. the number of molecules present
• D. the volume of the container

Explanation: Average translational kinetic energy per molecule is three halves kT, so it is the energy rather than the speed that is proportional to…

• A. creating cold and pumping it into the cabinet
• B. using work to move heat from a cold interior to the warmer room
• C. destroying heat inside the cabinet
• D. lowering the entropy of the universe

Explanation: Heat does not flow from cold to hot on its own, so a compressor does work to drive it that way, which is why the pipes at the back of the…

• A. increases by the work done
• B. decreases by the heat rejected
• C. returns to its original value, so the net heat supplied equals the net work done
• D. becomes zero

Explanation: Internal energy is a function of state, so returning to the same pressure, volume and temperature restores it exactly, and the first law…

• A. Isothermal
• B. Isobaric
• C. Isochoric
• D. Adiabatic

Explanation: Adiabatic means thermally isolated, so the system exchanges energy only as work.

• A. maximum
• B. zero
• C. equal to the heat supplied
• D. negative

Explanation: Work in this context is pressure multiplied by change in volume, and with no volume change there is no displacement of the surroundings…

• A. the total heat in a system
• B. the disorder of a system
• C. the temperature of a system
• D. the pressure of a system

Explanation: A system with many possible microscopic arrangements has high entropy, so melting ice or letting a gas expand into a vacuum both increase…

• A. the block with more mass becomes hotter
• B. both reach the same temperature
• C. both reach the same internal energy
• D. the hotter block loses all its energy

Explanation: Transfer continues only while a temperature difference exists, so equilibrium is reached when the temperatures match, not when the…

• A. Increase
• B. Decrease
• C. Remain constant
• D. Become zero

Explanation: The first law states that the change in internal energy equals the heat added plus the work done on the system, so with no work term every…