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JCECE Engineering JCECE Engineering Solved Paper-2013

  • 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\[2E\], then the wavelength must be changed to\[\lambda '\], where

    A) \[\lambda '>\lambda \]                

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

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

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

    Correct Answer: D

    Solution :

    We have,\[{{E}_{k}}=\frac{hc}{\lambda }-{{\phi }_{0}}\] and        \[2{{E}_{k}}=\frac{hc}{\lambda '}-{{\phi }_{0}}\] By the two relations, we have \[\lambda '>\frac{\lambda }{2}\] and        \[\lambda '<\lambda \] So,          \[\frac{\lambda }{2}<\lambda '<\lambda \]


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