Graphical Comparison of Thermodynamic Processes - Practice Questions & MCQ

1. Constant Volume Process:

Representation on P-V diagram:

This process is represented on the P-V  diagram by a vertical straight line as shown in figure, since V₁=V₂. 

Work done during the process:

$\mathrm{W}=\int_{\mathrm{V}_1}^{\mathrm{V}_2} \mathrm{Pdv}$

But $\mathrm{dv}=0$ for an isochoric process

$\therefore W=0$

Thus, work done during constant volume process is zero which is also evident from the P-V diagram as no area is enclosed by the vertical line on P-V diagram.

2. Constant Pressure Process:

Representation on P-V diagram:

During this process the pressure or the gas remains constant therefore it is represented by a horizontal line on P-V diagram. See figure.

Work done during the process:

$
\mathrm{W}=\int_{\mathrm{V}_1}^{\mathrm{V}_2} \mathrm{Pdv}
$
But P is constant.
$\therefore$ Work done $=P \int_{V_1}^{V_2} d v=P\left(V_2-V_1\right)$

The work done by the gas during constant pressure process is represented by a rectangle on P-V diagram.