Under an adiabatic process, the volume of an ideal gas gets doubled. Consequently the mean collision time between the gas molecule changes from ${\tau _1}$ to ${\tau _2}$ . If ${{{C_p}} \over {{C_v}}} = \gamma$ for this gas then a good estimate for ${{{\tau _2}} \over {{\tau _1}}}$ is given by :
Solution
$\tau$ $\propto$ ${V \over {\sqrt T }}$ ....(1)
<br><br>Also we know, PV<sup>$\gamma$</sup> = k
<br><br>We know, PV = nRT
<br><br>$\Rightarrow$ P $\propto$ ${T \over V}$
<br><br>$\therefore$ $\left( {{T \over V}} \right)$V<sup>$\gamma$</sup> = k
<br><br>$\Rightarrow$TV<sup>$\gamma$ - 1</sup> = k
<br><br>$\Rightarrow$ T $\propto$ V<sup>1 - $\gamma$</sup>
<br><br>Using this value in equation (1)
<br><br>$\tau$ $\propto$ ${V \over {{V^{{{1 - \gamma } \over 2}}}}}$
<br><br>$\Rightarrow$ $\tau$ $\propto$ ${{V^{1 - {{1 - \gamma } \over 2}}}}$
<br><br>$\Rightarrow$ $\tau$ $\propto$ ${{V^{{{\gamma + 1} \over 2}}}}$
<br><br>$\therefore$ ${{{\tau _2}} \over {{\tau _1}}}$ = ${\left( {{{2V} \over V}} \right)^{^{{{\gamma + 1} \over 2}}}}$ = ${\left( 2 \right)^{{{1 + \gamma } \over 2}}}$
About this question
Subject: Physics · Chapter: Thermodynamics · Topic: Zeroth and First Law
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