A monoatomic gas at pressure ' $\mathrm{P}$ ', having volume ' $\mathrm{V}$ ' expands isothermally to a…

A monoatomic gas at pressure ' $\mathrm{P}$ ', having volume ' $\mathrm{V}$ ' expands isothermally to a volume ' $2 \mathrm{~V}$ ' and then adiabatically to a volume ' $16 \mathrm{~V}$ '. The final pressure of the gas is (Take $\gamma=5 / 3$ )
  1. $\mathrm{P} / 64$
  2. $\mathrm{P} / 32$
  3. $16 \mathrm{P}$
  4. $32 \mathrm{P}$

Solution

After isothermal expansion: $\begin{aligned} & P_1 V_1=P_2 V_2 \\ & P_2=P_1 \frac{V_1}{V_2} \\ & P_2=P_1 \frac{V}{2 V} \\ & P_2=\frac{P}{2} \end{aligned}$ After adiabatic expansion: $\begin{aligned} & \mathrm{P}_2 \mathrm{~V}_2^\gamma=\mathrm{P}_3 \mathrm{~V}_3^\gamma \\ & \mathrm{P}_3=\mathrm{P}_2\left(\frac{\mathrm{V}_2}{\mathrm{~V}_3}\right)^\gamma \\ & \mathrm{P}_3=\frac{\mathrm{P}}{2}\left(\frac{2 \mathrm{~V}}{16 \mathrm{~V}}\right)^{5 / 3} \\ & \mathrm{P}_3=\frac{\mathrm{P}}{2}\left(\frac{1}{8}\right)^{5 / 3} \\ & \mathrm{P}_3=\frac{\mathrm{P}}{64} \end{aligned}$

Asked in: MHT CET 2023 (11 May Shift 1)

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