CMC Medical CMC-Medical Ludhiana Solved Paper-2012

  • question_answer
    An ideal gas is expanded adiabatically. How many times has the gas to be expanded to reduce the root mean square velocity of molecules two times? (y= 1.5)

    A)  2 times               

    B)  4 times

    C)  8 times                               

    D)  16 times

    Correct Answer: D

    Solution :

                    The root mean square velocity, \[{{v}_{rms}}=\sqrt{\frac{3RT}{M}}\Rightarrow {{v}_{rms}}=\sqrt{T}\] So, to reduce \[{{v}_{rms}}\] velocity 2 times, then temperature of the gas is to be reduced four times. i.e.,        \[\frac{T}{T}=\frac{1}{4}\] During adiabatic process \[T{{V}^{\gamma -1}}=T{{V}^{\gamma -1}}\] \[\Rightarrow \]               \[\frac{V}{V}={{\left( \frac{T}{T} \right)}^{\frac{1}{\gamma -1}}}={{(4)}^{\frac{1}{1.5-1}}}\]                       \[={{(4)}^{2}}=16\,\,\Rightarrow \,\,V=16\,V\]


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