JEE Main & Advanced JEE Main Online Paper (Held On 23 April 2013)

  • question_answer
    Electrons are accelerated through a potentialdifference V and protons are acceleratedthrough a potential difference 4 V. The de-Broglie wavelengths are  \[{{\lambda }_{e}}\] and \[{{\lambda }_{\operatorname{p}}}\] for electrons and protons respectively. The ratio of \[\frac{{{\lambda }_{e}}}{{{\lambda }_{\operatorname{P}}}}\] is given by: (given\[{{\operatorname{m}}_{e}}\]is mass of electron and\[{{\operatorname{m}}_{\operatorname{p}}}\]is mass of proton)     [JEE Main Online Paper ( Held On 23  April 2013 )

    A)  \[\frac{{{\lambda }_{e}}}{{{\lambda }_{\operatorname{P}}}}=\sqrt{\frac{{{\operatorname{m}}_{\operatorname{p}}}}{{{\operatorname{m}}_{\operatorname{e}}}}}\]                               

    B)                                         \[\frac{{{\lambda }_{e}}}{{{\lambda }_{\operatorname{P}}}}=\sqrt{\frac{{{\operatorname{m}}_{e}}}{{{\operatorname{m}}_{\operatorname{P}}}}}\]

    C)                                         \[\frac{{{\lambda }_{e}}}{{{\lambda }_{\operatorname{P}}}}=\frac{1}{2}\sqrt{\frac{{{\operatorname{m}}_{e}}}{{{\operatorname{m}}_{\operatorname{P}}}}}\]               

    D)                                         \[\frac{{{\lambda }_{e}}}{{{\lambda }_{\operatorname{P}}}}=2\sqrt{\frac{{{\operatorname{m}}_{\operatorname{P}}}}{{{\operatorname{m}}_{e}}}}\]

    Correct Answer: D

    Solution :

                      Energy in joule (E) = charge \[\times \]potential diff. in volt \[{{E}_{electron}}={{q}_{e}}V\]and\[{{E}_{proton}}={{q}_{p}}4V\] de-Broglie wavelength\[\lambda =\frac{h}{P}=\frac{h}{\sqrt{2mE}}\] \[{{\lambda }_{e}}=\frac{h}{\sqrt{2{{m}_{e}}eV}}\]and\[{{\lambda }_{p}}=\frac{h}{\sqrt{2{{m}_{P}}e4V}}\] \[(\because {{q}_{e}}={{q}_{P}})\] \[\therefore \]\[\frac{{{\lambda }_{e}}}{{{\lambda }_{P}}}=\frac{\frac{h}{\sqrt{2{{m}_{e}}eV}}}{\frac{h}{\sqrt{2{{m}_{P}}e4V}}}=\sqrt{\frac{2{{m}_{P}}e4V}{2{{m}_{e}}eV}}\] \[=2\sqrt{\frac{{{m}_{P}}}{{{m}_{e}}}}\] \[\therefore \] Greatest amount of heat generated by S.


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