JEE MAIN - Physics (2023 - 31st January Evening Shift - No. 11)
A hypothetical gas expands adiabatically such that its volume changes from 08 litres to 27 litres. If the ratio of final pressure of the gas to initial pressure of the gas is $\frac{16}{81}$. Then the ratio of $\frac{\mathrm{Cp}}{\mathrm{Cv}}$ will be.
$\frac{3}{1}$
$\frac{4}{3}$
$\frac{1}{2}$
$\frac{3}{2}$
Explanation
Let $\gamma$ be the ratio of $\frac{C_{p}}{C_{v}}$
Then for adiabatic process
$$ \begin{aligned} & P V^{\gamma}=\text { Constant } \\\\ & \Rightarrow \frac{P_{i}}{P_{f}}=\left(\frac{V_{f}}{V_{i}}\right)^{\gamma} \\\\ & \Rightarrow \frac{81}{16}=\left(\frac{27}{8}\right)^{\gamma} \\\\ & \Rightarrow \gamma=\frac{4}{3} \end{aligned} $$
Then for adiabatic process
$$ \begin{aligned} & P V^{\gamma}=\text { Constant } \\\\ & \Rightarrow \frac{P_{i}}{P_{f}}=\left(\frac{V_{f}}{V_{i}}\right)^{\gamma} \\\\ & \Rightarrow \frac{81}{16}=\left(\frac{27}{8}\right)^{\gamma} \\\\ & \Rightarrow \gamma=\frac{4}{3} \end{aligned} $$
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