Question
Which of the following is true for reversible adiabatic process involving an ideal gas?
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Solution
$PV^{\gamma} = K_{1}$
$\Rightarrow P = K_{1}.V^{- \gamma} $$$\Rightarrow \frac{dP}{dV} = K_{1}.( - \gamma).V^{- \gamma - 1} = - \gamma.\frac{P}{V}$$
The gas having higher $\gamma$ will have higher magnitude of slope of P vs. V curve.
Now, $n.\frac{R}{\gamma - 1}.dT = - P.dV = - \frac{nRT}{V}.dV$
Or, $\frac{dV}{dT} = - \frac{1}{\gamma - 1}.\frac{V}{T}$
Gas having higher $\gamma$ will have lower magnitude of slope of V vs. T curve.
Now, $n.C_{V,m}.dT = - P.dV = - \lbrack nRdT - V.dP\rbrack$
Or, $n.C_{P,m}.dT = - V.dP \Rightarrow \frac{n.\gamma R}{\gamma - 1}.dT = \frac{nRT}{P}.dP$
$\therefore\frac{dP}{dT} = \frac{\gamma}{\gamma - 1}.\frac{P}{T}$
Gas having higher $\gamma$will have lower magnitude of slope of P vs. T curve.
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