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JEE Main & Advanced Physics Photo Electric Effect, X- Rays & Matter Waves Question Bank Critical Thinking

  • question_answer
    Light from a hydrogen discharge tube is incident on the cathode of a photoelectric cell the work function of the cathode surface is 4.2 eV. In order to reduce the photo-current to zero the voltage of the anode relative to the cathode must be made                                                                              [DCE 2002]

    A)            ? 4.2 V                                    

    B)            ? 9.4 V

    C)            ? 17.8 V                                  

    D)            +9.4 V

    Correct Answer: B

    Solution :

                       \[E={{W}_{0}}+e{{V}_{0}}\]                    For hydrogen atom, \[E=+13.6\,eV\]                    \ + 13.6 = 4.2 + eV0                    Þ \[{{V}_{0}}=\frac{(13.6-4.2)\,eV}{e}=9.4\,V\]                    Potential at anode = ? 9.4 V


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