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KVPY Sample Paper KVPY Stream-SX Model Paper-25

  • question_answer
    When a metallic surface is illuminated with monochromatic light of wavelength \[\lambda ,\] the stopping potential is \[5\,{{V}_{0}}.\] When the same surface is illuminated with light of wavelength \[3\lambda ,\] the stopping potential is \[{{V}_{0}}.\] Then the work function of the metallic surface is:

    A) \[\frac{hc}{6\lambda }\]

    B) \[\frac{hc}{5\lambda }\]

    C) \[\frac{hc}{4\lambda }\]

    D) \[\frac{2\,hc}{4\lambda }\]

    Correct Answer: A

    Solution :

    \[\frac{hc}{\lambda }=5\,\,e{{V}_{0}}+\phi \]
    \[\frac{hc}{3\lambda }=\,\,e{{V}_{0}}+\phi \]    \[\Rightarrow \]   \[\frac{2hc}{3\lambda }=\,\,4e{{V}_{0}}\] \[\Rightarrow \]   \[\phi =\frac{hc}{6\lambda }\]    Ans.


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