Thermodynamics

JEE Main level, single correct, medium

89 of 190

Question 89 of 190

A sample of gas at temperature TT is adiabatically expanded to double its volume. Adiabatic constant for the gas is γ=3/2\gamma=3 / 2. The work done by the gas in the process is:
(μ=1 mole)(\mu=1 \mathrm{~mole})

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Answer: (C) RT[2−2]R T[2-\sqrt{2}]

W=nRΔT1−γTVγ−1= constan t=Tf(2 V)γ−1 Tf=T(12)1/2=T2 W=R(T2−T)1−32=2RT(2−1)2=RT(2−2)\begin{aligned} & \mathrm{W}=\frac{\mathrm{nR} \Delta \mathrm{T}}{1-\gamma} \\ & \mathrm{TV}^{\gamma-1}=\text { constan } \mathrm{t}=\mathrm{T}_{\mathrm{f}}(2 \mathrm{~V})^{\gamma-1} \\ & \mathrm{~T}_{\mathrm{f}}=\mathrm{T}\left(\frac{1}{2}\right)^{1 / 2}=\frac{\mathrm{T}}{\sqrt{2}} \\ & \mathrm{~W}=\frac{\mathrm{R}\left(\frac{\mathrm{T}}{\sqrt{2}}-\mathrm{T}\right)}{1-\frac{3}{2}}=2 \mathrm{RT} \frac{(\sqrt{2}-1)}{\sqrt{2}} \\ & =\mathrm{RT}(2-\sqrt{2})\end{aligned}

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