From the first law of thermodynamics, we know, dU = dQ - dW ; (work done BY the system is considered +ve)For an adiabatic process, dQ = 0, and hence, dU = -dWFor an ideal gas expansion, we see that work done BY the system is +ve (recall the sign convention for work done), i.e., dW > 0. Therefore, dU is less than 0, and thus, the internal energy decreases.

Adiabatic Process and Internal Energy of Gas

An adiabatic process is one where there is no heat exchange between the system and the surroundings. In other words, there is no transfer of thermal energy in or out of the system. In such a process, the internal energy of the gas can change in different ways depending on the conditions.

Internal energy refers to the sum of the kinetic and potential energies of the molecules in a system. It is a measure of the total energy contained within the system, which includes both the thermal and non-thermal components.

Explanation of the Answer

In an adiabatic process, the internal energy of the gas decreases. This is because the gas is compressed or expanded rapidly, which causes the temperature to change without any transfer of heat. The work done on the gas during compression or expansion is converted into internal energy, which results in an increase in the temperature of the gas.

However, since there is no heat exchange with the surroundings, the internal energy of the gas remains constant. This means that the change in the internal energy of the gas is zero, and hence, the correct answer to the question is option D - "Decreases".

Summary

- An adiabatic process is one where there is no heat exchange between the system and the surroundings.
- Internal energy refers to the sum of the kinetic and potential energies of the molecules in a system.
- In an adiabatic process, the internal energy of the gas decreases due to rapid compression or expansion.
- Since there is no heat exchange with the surroundings, the internal energy of the gas remains constant.