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

  • question_answer
    When a metal surface is illuminated by light of wavelengths 400 nm and 250 nm, the maximum velocities of the photoelectrons ejected are \[v\] and \[2v\] respectively. The work function of the metal is (h = Planck?s constant, c = velocity of light in air)                                    [EAMCET (Engg.) 2000]

    A)            \[2\,hc\,\times {{10}^{6}}\,J\]                                          

    B)            \[1.5\,hc\,\times {{10}^{6}}\,J\]

    C)            \[hc\,\times {{10}^{6}}\,J\]   

    D)            \[0.5\,\,hc\,\times {{10}^{6}}\,J\]

    Correct Answer: A

    Solution :

                       By using \[\frac{hc}{\lambda }={{W}_{0}}+\frac{1}{2}m{{v}^{2}}\]                    \[\Rightarrow \frac{hc}{400\times {{10}^{-9}}}={{W}_{0}}+\frac{1}{2}m{{v}^{2}}\]                          ?..(i)                    and \[\frac{hc}{250\times {{10}^{-9}}}={{W}_{0}}+\frac{1}{2}m{{(2v)}^{2}}\]                     ?..(ii)                    On solving (i) and (ii)                    \[\frac{1}{2}m{{v}^{2}}=\frac{hc}{3}\left[ \frac{1}{250\times {{10}^{-9}}}-\frac{1}{400\times {{10}^{-9}}} \right]\]  ?..(iii)            From equation (i) and (iii) \[{{W}_{0}}=2hc\times {{10}^{6}}J\].


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