NEET Sample Paper NEET Sample Test Paper-25

  • question_answer A photosensitive metallic surface has work function, \[h\,{{v}_{0}}.\]If photons of energy\[2h{{v}_{0}}\]fall on this surface, the electrons come out with a maximum velocity of\[4\times {{10}^{6}}\,m/s.\]When the photon energy is increased to\[5h{{v}_{0}},\]then maximum velocity of photoelectrons will be

    A) \[2\times {{10}^{6}}\,m/s\]

    B) \[2\times {{10}^{7}}\,m/s\]

    C) \[8\times {{10}^{5}}\,m/s\]

    D) \[8\times {{10}^{6}}\,m/s\]

    Correct Answer: D

    Solution :

     Einstein's photoelectric equation can be written as \[\frac{1}{2}m{{v}^{2}}=hv-\phi \] \[\Rightarrow \]\[\frac{1}{2}m\times {{(4\times {{10}^{6}})}^{2}}=2h{{v}_{0}}-h{{v}_{0}}\]                     (i) and \[\frac{1}{2}m\times {{v}^{2}}=5h{{v}_{0}}-h{{v}_{0}}\]                       (ii) Dividing Eq. (ii) by (i), we get \[\frac{{{v}^{2}}}{{{(4\times {{10}^{6}})}^{2}}}=\frac{4h{{v}_{0}}}{h{{v}_{0}}}\] \[\Rightarrow \]\[{{v}^{2}}=4\times 16\times {{10}^{12}}\Rightarrow \,\,{{v}^{2}}=64\times {{10}^{12}}\] \[\Rightarrow \]\[v=8\times {{10}^{6}}\,m/s\]

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