NEET Sample Paper NEET Sample Test Paper-92

  • question_answer
    When a metal surface is illuminated by light of wavelengths 400 nm and 250 nm, the maximum velocities of the photoelectrons ejected are \[\upsilon \] and \[2\upsilon \] respectively. The work function of the metal is (h = Planck's constant, c = velocity of light in air)

    A) \[2\,\,hc\times {{10}^{6}}J\]    

    B)        \[1.5\,\,hc\times {{10}^{6}}J\]

    C) \[hc\times {{10}^{6}}J\]          

    D)        \[0.5\,\,hc\times {{10}^{6}}J\]

    Correct Answer: A

    Solution :

    [a] By using \[\frac{hc}{\lambda }={{W}_{0}}+\frac{1}{2}m{{\upsilon }^{2}}\] \[\Rightarrow \]\[\frac{hc}{400\times {{10}^{-9}}}={{W}_{0}}+\frac{1}{2}m{{\upsilon }^{2}}\]                       ?(i) and \[\frac{hc}{250\times {{10}^{-9}}}={{W}_{0}}+\frac{1}{2}m{{(2\upsilon )}^{2}}\]                      ?(ii) On solving (i) and (ii) \[\frac{1}{2}m{{\upsilon }^{2}}=\frac{hc}{3}\left[ \frac{1}{250\times {{10}^{-9}}}-\frac{1}{400\times {{10}^{-9}}} \right]\]  ?(iii) From equation (i) and (iii) \[{{W}_{0}}=2hc\times {{10}^{6}}J.\]


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