JEE Main & Advanced Sample Paper JEE Main Sample Paper-9

  • question_answer
    The ratio of de-Broglei wavelength of molecules of hydrogen & helium which are at temperatures \[27{}^\circ C\text{ }\And \text{ }127{}^\circ C\] respectively

    A) \[\sqrt{\frac{5}{3}}\]                                     

    B) \[\sqrt{\frac{8}{3}}\]

    C) \[\sqrt{\frac{3}{8}}\]                                     

    D) \[\sqrt{\frac{3}{5}}\]

    Correct Answer: B

    Solution :

    de-Broglei wavelength is,\[\lambda =\frac{h}{mv}\] From \[KTG,{{v}_{rms}}=\sqrt{\frac{3KT}{m}}\] where m is mass of gas molecule. So,\[\frac{{{\lambda }_{H}}}{{{\lambda }_{He}}}=\frac{{{m}_{He}}{{v}_{He}}}{{{m}_{H}}{{v}_{H}}}=\sqrt{\frac{{{m}_{He}}{{T}_{He}}}{{{m}_{H}}{{T}_{H}}}}\]\[=\sqrt{\frac{4\times 400}{2\times 300}}=\sqrt{\frac{8}{3}}\]


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