BCECE Engineering BCECE Engineering Solved Paper-2004

  • question_answer
    If mass of He is 4 times that of hydrogen, then mean velocity of He is:

    A)  2 times of H-mean value

    B)        \[\frac{1}{2}\]times of H-mean value

    C)         4 times of H-mean value

    D)         same as H-mean value

    Correct Answer: B

    Solution :

    Average speed or mean speed of gas molecules \[\bar{v}=\sqrt{\frac{8RT}{\pi M}}\] or            \[\bar{v}\propto \frac{1}{\sqrt{M}}\] or            \[\frac{{{{\bar{v}}}_{H}}}{{{{\bar{v}}}_{He}}}=\sqrt{\frac{{{M}_{He}}}{{{M}_{H}}}}\] Here,   \[{{M}_{He}}=4{{M}_{H}}\] \[\therefore \]  \[\frac{{{{\bar{v}}}_{H}}}{{{{\bar{v}}}_{He}}}=\sqrt{\frac{4}{1}}=2\] or            \[{{\bar{v}}_{He}}=\frac{1}{2}{{\bar{v}}_{H}}\]


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