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

  • question_answer
    A photosensitive metallic surface has work function \[h{{v}_{0}}\]. If photons of energy \[2h{{v}_{0}}\] fall on this surface the electrons come out with a maximum velocity of \[4\times {{10}^{6}}\,m/s\]. When the photon energy is increases to \[5h{{v}_{0}}\] then maximum velocity of photo electron will be      [CBSE PMT 2005]

    A)            \[2\times {{10}^{6}}\,m/s\]   

    B)            \[2\times {{10}^{7}}\,m/s\]

    C)            \[8\times {{10}^{5}}\,m/s\]   

    D)            \[8\times {{10}^{6}}\,m/s\]

    Correct Answer: D

    Solution :

                       From \[E={{W}_{0}}+\frac{1}{2}mv_{\max }^{2}\] Þ \[2h{{\nu }_{0}}=h{{\nu }_{0}}+\frac{1}{2}mv_{1}^{2}\] Þ \[h{{\nu }_{0}}=\frac{1}{2}mv_{1}^{2}\]       .....(i) and \[5h{{\nu }_{0}}=h{{\nu }_{0}}+\frac{1}{2}mv_{2}^{2}\] Þ \[4h{{\nu }_{0}}=\frac{1}{2}mv_{2}^{2}\]   .....(ii)                    Dividing equation (ii) by (i) \[{{\left( \frac{{{v}_{2}}}{{{v}_{1}}} \right)}^{2}}=\frac{4}{1}\]             Þ \[{{v}_{2}}=2{{v}_{1}}=2\times 4\times {{10}^{6}}=8\times {{10}^{6}}m/s\]


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