J & K CET Medical J & K - CET Medical Solved Paper-2004

  • question_answer
    At what temperature the rms velocity of helium molecules will be equal to that of hydrogen moelcules at NTP?

    A)  844 K                                   

    B)  64 K

    C) \[273{}^\circ C\]

    D)  273 K

    Correct Answer: C

    Solution :

                    The root mean square velocity \[{{v}_{rms}}=\sqrt{\frac{3RT}{M}}\] where R is gas constant, T the absolute temperature and M the molecular weight. Given, \[{{v}_{He}}={{v}_{H}},\]\[{{T}_{H}}=273\,K,\]\[{{M}_{H}}=2,\]    \[{{M}_{He}}=4\] \[\therefore \]  \[\frac{{{v}_{He}}}{{{v}_{H}}}=\sqrt{\frac{{{T}_{H}}}{{{T}_{He}}}\times \frac{{{M}_{He}}}{{{M}_{H}}}}\]                 \[1=\sqrt{\frac{273}{{{T}_{He}}}\times \frac{4}{2}}\] \[\Rightarrow \]               \[{{T}_{He}}=546\,K\] In \[{}^\circ C,\] \[{{T}_{He}}=(546-273){}^\circ C=273{}^\circ C\]


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