Q.Explain in detail the isochoric process.

Step 1. An isochoric process holds volume $V$ fixed; from $PV=\mu RT$, $P\propto T$, giving a straight $P$-$T$ line through the origin, and on a P-V diagram, a vertical line.

Step 2. Since $\Delta V=0$ throughout, the work done is $W=\int P\,dV=0$ -- no work is possible at all, regardless of how much pressure or temperature change.

Step 3. Applying the first law with $W=0$: $\Delta U=Q$ -- ALL of the supplied (or released) heat goes entirely into changing internal energy, so heating at constant volume raises both temperature and pressure together, and cooling lowers both together. …

Note $\Delta V=0$ forces $W=0$ regardless of the process's other details, …

• Assuming temperature stays constant in an isochoric process -- it is VOLUME that is fixed, not temperature; …