MHTCET 20 Apr 2026 Shift 2 Paper

Concept:For an ideal gas, internal energy depends only on its temperature.In an adiabatic process, $Q = 0$, so any work done by the gas comes from its own internal energy.Explanation:In an isothermal process, temperature $T$ is constant.Therefore, for an ideal gas, $\Delta U = 0$ for both isothermal expansion and isothermal compression.So, options A and B are incorrect because internal energy does not change.For an adiabatic process, no heat is exchanged with the surroundings, so $Q = 0$.Using the first law of thermodynamics: $\Delta U = Q - W$, where $W$ is the work done by the gas.During adiabatic expansion, the gas does work on the surroundings, so $W > 0$.Thus, $\Delta U = -W$, which gives $\Delta U < 0$.Hence, the internal energy decreases during adiabatic expansion.During adiabatic compression, work is done on the gas, so $W < 0$ and $\Delta U > 0$.Thus, the internal energy increases in adiabatic compression.Answer:The correct option is C: Adiabatic expansion of an ideal gas.