J & K CET Engineering J and K - CET Engineering Solved Paper-2004

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

    A)  \[844\text{ }K\]        

    B)  \[64\text{ }K\]

    C)  \[{{273}^{o}}C\]      

    D)  \[273\text{ }K\]

    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,    \[{{v}_{He}}={{v}_{H}},\,\,\,\,\,{{T}_{H}}=273K,\,\,\,\,\,\,\,\,{{M}_{H}}=2,\,\,\,\,{{M}_{He}}=4\] \[\therefore \] \[\frac{{{v}_{He}}}{{{v}_{H}}}=\sqrt{\frac{{{T}_{H}}}{{{T}_{He}}}\times \frac{{{M}_{He}}}{{{M}_{H}}}}\] \[1=\sqrt{\frac{273}{{{T}_{He}}}\times \frac{4}{2}}\] \[\Rightarrow \] \[{{T}_{He}}=546K\] In  \[^{o}C,\] \[{{T}_{He}}={{(546-273)}^{o}}C={{273}^{o}}C\]


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