JEE Main & Advanced Physics Photo Electric Effect, X- Rays & Matter Waves Question Bank Matter Waves

  • question_answer
    The energy that should be added to an electron, to reduce its de-Broglie wavelengths from \[{{10}^{-10}}\]m to \[0.5\times {{10}^{-10}}\]m, will be   [KCET (Engg./Med.) 2000]

    A)            Four times the initial energy

    B)            Thrice the initial energy

    C)            Equal to the initial energy

    D)            Twice the initial energy

    Correct Answer: B

    Solution :

                       \[\lambda =\frac{h}{\sqrt{2mE}}\Rightarrow \lambda \propto \frac{1}{\sqrt{E}}\Rightarrow \frac{{{\lambda }_{1}}}{{{\lambda }_{2}}}=\sqrt{\frac{{{E}_{2}}}{{{E}_{1}}}}\]                    \[\Rightarrow \frac{{{10}^{-10}}}{0.5\times {{10}^{-10}}}=\sqrt{\frac{{{E}_{2}}}{{{E}_{1}}}}\Rightarrow {{E}_{2}}=4{{E}_{1}}\]            Hence added energy \[={{E}_{2}}-{{E}_{1}}=3{{E}_{1}}\]


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