$T _{1} V _{1}^{ \gamma -1}= T _{2} V _{2}^{ \gamma -1}$
$\frac{ T _{2}}{ T _{1}}=\left(\frac{ V _{1}}{ V _{2}}\right)^{ \gamma -1}$
Substitute the values.
$\frac{ T _{2}}{ T _{1}}=\left(\frac{1}{3}\right)^{1.5-1}$
$=\frac{1}{\sqrt{3}}$
The efficiency is given as,
$\eta=1-\frac{ T _{2}}{ T _{1}}$
$=1-\frac{1}{\sqrt{3}}$

| Process | Condition |
| $(I)$ Adiabatic | $(A)\; \Delta W =0$ |
| $(II)$ Isothermal | $(B)\; \Delta Q=0$ |
| $(III)$ Isochoric | $(C)\; \Delta U \neq 0, \Delta W \neq 0 \Delta Q \neq 0$ |
| $(IV)$ Isobaric | $(D)\; \Delta U =0$ |

