Internal Energy and Heat

Internal energy is a fundamental concept in thermodynamics that refers to the total energy contained within a system. It includes the kinetic and potential energies of the particles that make up the system.

Heat
Heat is a form of energy transfer that occurs due to a temperature difference between two objects or systems. It flows from a region of higher temperature to a region of lower temperature until thermal equilibrium is reached.

Constant Volume
In a constant volume process, the volume of the system remains constant throughout. This means that no work is done by or on the system, and any change in energy is solely due to heat transfer.

Constant Pressure
In a constant pressure process, the pressure of the system remains constant throughout. This allows work to be done by or on the system, in addition to heat transfer.

Constant Temperature
In a constant temperature process, the temperature of the system remains constant throughout. This means that the average kinetic energy of the particles remains constant, and any change in energy is solely due to heat transfer.

Constant Moles
In a constant moles process, the number of moles of a substance in the system remains constant throughout. This means that the composition of the system does not change, and any change in energy is solely due to heat transfer.

Heat Evolved or Absorbed
The question asks whether the internal energy is the heat evolved or absorbed. In a constant volume process, the volume remains constant, so no work is done. Therefore, any change in energy is solely due to heat transfer. This means that the internal energy is equal to the heat evolved or absorbed.

Conclusion
The correct answer is option 'B', constant volume. In a constant volume process, the internal energy is equal to the heat evolved or absorbed.