Free Thermal Equilibrium and Heat MCQs with Answers

1. Two bodies are in thermal equilibrium when

• 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 different amounts of internal energy. A cup of tea and a swimming pool at the same temperature are in equilibrium despite the pool storing far more energy. This is the content of the zeroth law, which is what makes a thermometer possible.

2. Heat is best described as

• 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 to contain heat. Temperature measures the average kinetic energy of the particles and decides which way the transfer goes. The old caloric fluid picture was abandoned once friction was shown to generate heat without limit.

3. Absolute zero on the Kelvin scale corresponds to

• 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 motion reaches its minimum. Converting between the scales means adding or subtracting 273, since a kelvin and a Celsius degree are the same size. Every gas law formula requires absolute temperature.

4. The heat required to raise the temperature of a body is given by

• 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 one kilogram by one kelvin. Water has an unusually high value of about 4200 J per kg per K, which is why it is used as a coolant. During melting or boiling this formula does not apply, because the temperature does not change.

5. While ice at 0 degrees Celsius is melting, the heat supplied

• 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 until all the ice has gone. This is why a mixture of ice and water is a reliable fixed point for calibrating a thermometer. The internal energy rises even though the temperature does not.

6. Two blocks at different temperatures are placed in contact in an insulated box. Heat flows until

• 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 energies do. The heat lost by the hotter block equals the heat gained by the cooler one, which is the principle used in calorimetry. The final temperature depends on both masses and both specific heat capacities.