BCECE Engineering BCECE Engineering Solved Paper-2006

  • question_answer
    The de-Broglie wavelength of an electron, \[\alpha \]-particle and a proton all having the same kinetic energy is respectively given as \[{{\lambda }_{e,}}{{\lambda }_{\alpha }}\] and \[{{\lambda }_{P.}}\] Then which of the following is not true ?

    A)  \[{{\lambda }_{e}}>{{\lambda }_{P}}\]                                 

    B)        \[{{\lambda }_{p}}>{{\lambda }_{\alpha }}\]

    C)        \[{{\lambda }_{e}}>{{\lambda }_{\alpha }}\]                                       

    D)        \[{{\lambda }_{\alpha }}<{{\lambda }_{p}}<{{\lambda }_{e}}\]

    Correct Answer: A

    Solution :

    de-Broglie wavelength \[\lambda =\frac{h}{mv}\]or \[\lambda \propto \frac{1}{m}\] \[\therefore \]\[{{\lambda }_{e}}\propto \frac{1}{{{m}_{e}}},{{\lambda }_{\alpha }}\propto \frac{1}{{{m}_{\alpha }}}\]and  \[{{\lambda }_{p}}\propto \frac{1}{{{m}_{p}}}\] As we know that \[{{m}_{e}}<{{m}_{p}}<{{m}_{a}}\] So,          \[{{\lambda }_{e}}>{{\lambda }_{p}}>{{\lambda }_{\alpha }}\] or        \[{{\lambda }_{e}}>{{\lambda }_{\alpha }}\]or \[{{\lambda }_{p}}>{{\lambda }_{\alpha }}\]or \[{{\lambda }_{e}}>{{\lambda }_{p}}\]


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