NEET Physics Photo Electric Effect, X- Rays & Matter Waves NEET PYQ-Photo Electric Effect,X-Rays

  • question_answer
    A photoelectric surface is illuminated successively by monochromatic light of wavelength\[\lambda \] and\[\frac{\lambda }{2}\]. If the maximum kinetic energy of the emitted photoelectrons in the second case is 3 times that in the first case, the work function of the surface of the material is (A = Planck's constant, c = speed of light)                                                                         [NEET (Re) 2015]

    A)  \[\frac{hc}{2\lambda }\]           

    B)  \[\frac{hc}{\lambda }\]

    C)  \[\frac{2hc}{\lambda }\]           

    D)       \[\frac{hc}{3\lambda }\]

    Correct Answer: A

    Solution :

    According to Einstein's photoelectric equation,
    \[E={{K}_{\max }}+\phi \]
    where, \[{{K}_{\max }}\] is maximum kinetic energy of emitted electron and \[\phi \] is work function of an electron.
    \[{{K}_{\max }}=E-\phi =hv-\phi \]
    \[{{K}_{\max }}=\frac{hc}{\lambda }-\phi \]                   …(i)
    Similarly, in second case, maximum kinetic energy of emitted electron is 3 times that in first case, we get
                \[3{{K}_{\max }}=\frac{hc}{\frac{\lambda }{2}}-\phi \]              …(ii)
    Solving Eqs. (i) and (ii), we get work function of an emitted electron from a metal surface.
    \[\phi =\frac{hc}{2\lambda }\]


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