Question

Three moles of an ideal gas ($C_P=\frac{7}{2}R$) at pressure, $P_A$ and temperature $T_A$ is isothermally expanded to twice its initial volume. It is then compressed at constant pressure to its original volume. Finally gas is compressed at constant volume to its original pressure $P_A$.
The correct $P-V$ and $P-T$ diagrams for the complete process are

• A.
• B.
• C.
• D.

Answer 1

Answer: (A), (C)

Let the process start from initial pressure $P_A$, volume $V_A$ and temperature $T_A$.
$I:$ Isothermal expansion $(PV=$constant $)$ at temperature $T_A$ to twice the initial volume $V_A$

$II:$ Compression at constant pressure $P_A/2$ to original volume $V_A$ (i.e. V $\propto$ T)

$III:$ Isochoric process $($at volume $V_A)$ to initial conditions (i.e. P $\propto$ T )

Why this question? Importance in JEE: graph based questions involving different processes are frequently asked in JEE.