NEET Sample Paper NEET Sample Test Paper-65

  • 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

    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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