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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 wavelength from one nm to 0.5 nm is [KCET 2005]

    A)            Four times the initial energy 

    B)            Equal to the initial energy

    C)            Twice the initial energy           

    D)            Thrice the initial energy

    Correct Answer: D

    Solution :

               \[\lambda =\frac{\hbar }{\sqrt{2mE}}\];\[\frac{\lambda '}{\lambda }=\sqrt{\frac{E}{E'}}\]Þ\[\frac{E}{E}={{\left( \frac{0.5}{1} \right)}^{2}}\]Þ\[E'=\frac{E}{0.25}=4E\] The energy should be added to decrease wavelength.                    \[=E'-E=3E\]


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