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

  • question_answer
    Mercury violet light \[(\lambda =4558{AA})\] is falling on a photosensitive material \[(\varphi =2.5eV)\]. The speed of the ejected electrons is in \[m{{s}^{-1}}\], about                         [AMU (Engg.) 1999]

    A) \[3\times {{10}^{5}}\]      

    B) \[{{K}_{A}}={{K}_{B}}/2\]

    C) \[4\times {{10}^{4}}\]      

    D) \[3.65\times {{10}^{7}}\]

    Correct Answer: B

    Solution :

    By using\[E={{W}_{0}}+\frac{1}{2}mv_{\max }^{2}\]; where \[E=\frac{12375}{4558}=2.71\ eV\]                    \[\Rightarrow 2.71\ eV=2.5\ eV+\frac{1}{2}\times 9.1\times {{10}^{-31}}\times v_{\max }^{2}\]                    \[\Rightarrow 0.21\times 1.6\times {{10}^{-19}}=\frac{1}{2}\times 9.1\times {{10}^{-31}}\times v_{\max }^{2}\]            \[\Rightarrow {{v}_{\max }}=2.65\times {{10}^{5}}\ m/s\]


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