JEE Main & Advanced JEE Main Solved Paper-2015

  • question_answer
    Consider an ideal gas confined in an isolated closed chamber. As the gas undergoes an adiabatic expansion, the average time of collision between molcules increases as \[{{V}^{q}},\] where V is the volume of the gas. The value of q is : \[\left( \gamma =\frac{{{C}_{p}}}{{{C}_{v}}} \right)\] [JEE Main Solved Paper-2015 ]

    A) \[\frac{\gamma +1}{2}\]              

    B) \[\frac{\gamma -1}{2}\]

    C) \[\frac{3\gamma +5}{6}\]                            

    D) \[\frac{3\gamma -5}{6}\]

    Correct Answer: A

    Solution :

    Average time of collisim between molecules is \[t=\frac{\lambda }{{{v}_{rms}}}\]mean free path \[\lambda \frac{1}{\pi {{d}^{2}}N/V}=\frac{V}{\pi {{d}^{2}}N}\]                      \[\lambda \propto V\] \[{{v}_{rms}}\propto \sqrt{T}\]                 So\[t\propto \frac{V}{\sqrt{T}}\] \[t\propto V.{{T}^{\frac{-1}{2}}}\]and\[V{{T}^{\gamma =1}}=\]constant \[t\propto V.{{\left( {{V}^{1-\gamma }} \right)}^{\frac{-1}{2}}}\] \[t\propto V.{{V}^{\frac{r-1}{2}}}\] \[\]So\[q=\frac{\gamma +1}{2}\]


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