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JEE Main & Advanced Physics EM Waves Question Bank Mock Test - Electromagnetic Waves and Dual Nature

  • 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

    A) -4.2V   

    B) -9.4V

    C) -17.8V  

    D) +9.4 V

    Correct Answer: B

    Solution :

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


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