CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2011

  • question_answer
    An electron of mass me and a proton of mass \[{{m}_{p}}\] are moving with the same speed. The ratio of their de-Broglie's wavelengths \[{{\lambda }_{e}}/{{\lambda }_{p}}\]is

    A)  1                                            

    B)  1836

    C)  1836                                     

    D)  918

    Correct Answer: B

    Solution :

    de-Broglie's wavelength,                                 \[\lambda =\frac{h}{mv}\]                 For electron,                                 \[{{\lambda }_{e}}=\frac{h}{{{m}_{e}}v}\] For photon,                                 \[{{\lambda }_{P}}=\frac{h}{{{m}_{p}}v}\] \[\therefore \]                  \[\frac{{{\lambda }_{e}}}{{{\lambda }_{p}}}=\frac{h/{{m}_{e}}v}{h/{{m}_{p}}v}\]                                 \[\frac{{{\lambda }_{e}}}{{{\lambda }_{p}}}=\frac{{{m}_{p}}}{{{m}_{e}}}\]                  \[\frac{{{\lambda }_{e}}}{{{\lambda }_{p}}}=\frac{1.67\times {{10}^{-27}}}{9.1\times {{10}^{-31}}}=0.18\times {{10}^{4}}=1836\]


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