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A sample of $1$ mole gas at temperature $\mathrm{T}$ is adiabatically expanded to double its volume. If adiabatic constant for the gas is $\gamma=\frac{3}{2}$, then the work done by the gas in the process is:
$\mathrm{RT}[2-\sqrt{2}]$
$\frac{\mathrm{R}}{\mathrm{T}}[2-\sqrt{2}]$
$\mathrm{RT}[2+\sqrt{2}]$
$\frac{T}{R}[2+\sqrt{2}]$
Solution
$\mathrm{TV}^{\gamma-1}=\text { constant }$
$\Rightarrow \mathrm{T}(\mathrm{V})^{\frac{3}{2}-1}=\mathrm{T}_{\mathrm{f}}(2 \mathrm{~V})^{\frac{3}{2}-1}$
$\Rightarrow \mathrm{TV}^{\frac{1}{2}}=\mathrm{T}_{\mathrm{f}}(2)^{\frac{1}{2}}(\mathrm{~V})^{\frac{1}{2}}$
$\Rightarrow \mathrm{T}_{\mathrm{f}}=\left(\frac{\mathrm{T}}{\sqrt{2}}\right)$
$\text { Now, W.D. }=\frac{\mathrm{nR} \Delta \mathrm{T}}{1-\gamma}=\frac{1 \cdot \mathrm{R}\left[\frac{\mathrm{T}}{\sqrt{2}}-\mathrm{T}\right]}{1-\frac{3}{2}}$
$\Rightarrow \text { W.D. }=2 \mathrm{RT}\left[1-\frac{1}{\sqrt{2}}\right]$
$\Rightarrow \text { W.D. }=\mathrm{RT}[2-\sqrt{2}]$