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

  • question_answer
    Two identical photo-cathodes receive light of frequencies \[{{f}_{1}}\] and \[{{f}_{2}}\]. If the velocities of the photo electrons (of mass \[m\]) coming out are respectively \[{{v}_{1}}\] and \[{{v}_{2}}\], then            [AIEEE 2003]

    A)            \[{{v}_{1}}-{{v}_{2}}={{\left[ \frac{2h}{m}\left( {{f}_{1}}-{{f}_{2}} \right) \right]}^{1/2}}\]

    B)            \[v_{1}^{2}-v_{2}^{2}=\frac{2h}{m}\left( {{f}_{1}}-{{f}_{2}} \right)\]

    C)            \[{{v}_{1}}+{{v}_{2}}={{\left[ \frac{2h}{m}\left( {{f}_{1}}+{{f}_{2}} \right) \right]}^{1/2}}\]

    D)            \[v_{1}^{2}+v_{2}^{2}=\frac{2h}{m}\left( {{f}_{1}}+{{f}_{2}} \right)\]

    Correct Answer: B

    Solution :

                       Using Einstein photoelectric equation \[E={{W}_{0}}+{{K}_{\max }}\]                      \[h{{f}_{1}}={{W}_{0}}+\frac{1}{2}mv_{1}^{2}\]                                              ?..(i)                    \[h{{f}_{2}}={{W}_{0}}+\frac{1}{2}mv_{2}^{2}\]                                              ?..(ii)                \[\Rightarrow h({{f}_{1}}-{{f}_{2}})=\frac{1}{2}m(v_{1}^{2}-v_{2}^{2})\]\[\Rightarrow (v_{1}^{2}-v_{2}^{2})=\frac{2h}{m}({{f}_{1}}-{{f}_{2}})\]


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