Question

In which of the following processes the internal energy of system remain constant?

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

Hint:

Internal energy of an ideal gas depends only on temperature.

Answer 1

The Correct Option is C

Step 1: Idea:
Use $\Delta U = nC_V\Delta T$ for an ideal gas. $\Delta U$ is zero only if $\Delta T = 0$.

Step 2: Which process keeps T fixed?:
The word isothermal literally means 'same temperature', so it is the process with $\Delta T = 0$ and hence $\Delta U = 0$.
In the other three, temperature moves: heating at constant pressure (isobaric), heating at constant volume (isochoric), and cooling or heating through work alone (adiabatic, where $q=0$ but $\Delta U = w$).

Final Answer:
Only the isothermal process keeps the internal energy constant, which is option (C). \[ \boxed{\text{Isothermal process}} \]