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

  • question_answer
    Light of wavelength \[\lambda \]strikes a photo-sensitive surface and electrons are ejected with kinetic energy E. If  the kinetic energy is to be increased to 2E, the wavelength must be changed to \[\lambda '\] where                                          [MP PET 1997]

    A)            \[\lambda '=\frac{\lambda }{2}\]                                    

    B)            \[\lambda '=2\lambda \]

    C)            \[\frac{\lambda }{2}<\lambda '<\lambda \]               

    D)            \[\lambda '>\lambda \]

    Correct Answer: C

    Solution :

                       \[E=\frac{hc}{\lambda }-{{W}_{0}}\] and \[2E=\frac{hc}{\lambda '}-{{W}_{0}}\]                    \[\Rightarrow \frac{\lambda '}{\lambda }=\frac{E+{{W}_{0}}}{2E+{{W}_{0}}}\Rightarrow \lambda '=\lambda \left( \frac{1+{{W}_{0}}/E}{2+{{W}_{0}}/E} \right)\]                    Since \[\frac{(1+{{W}_{0}}/E)}{(2+{{W}_{0}}/E)}>\frac{1}{2}\] so \[\lambda '>\frac{\lambda }{2}\]


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