NEET Physics Photo Electric Effect, X- Rays & Matter Waves NEET PYQ-Photo Electric Effect,X-Rays

  • question_answer
    The photoelectric threshold wavelength of silver is \[3250\times {{10}^{-10}}m\]. The velocity of the electron ejected from a silver surface by ultraviolet light of wavelength \[2536\times {{10}^{-10}}m\] is                               [NEET-2017] (Given \[h=4.14\times {{10}^{-15}}eVs\] and \[c=3\times {{180}^{8}}\,m{{s}^{-1}}\])

    A)  \[\approx 0.3\times {{10}^{6}}\,m{{s}^{-1}}\]

    B)       \[v=0.6\times {{10}^{6}}\,m/s\]

    C)  \[\approx 0.6\times {{10}^{6}}\,m{{s}^{-1}}\]

    D)       \[\approx 61\times {{10}^{3}}\,m{{s}^{-1}}\]

    Correct Answer: C

    Solution :

    (b & c)* Both answers are correct.
    \[{{\lambda }_{0}}=3250\times {{10}^{-10}}\,m\]
    \[\lambda =2536\times {{10}^{-10}}\,m\]
    \[\phi =\frac{1242\,eV-nm}{325\,nm}=3.82\,eV\]
    \[hv=\frac{1242\,eV-nm}{253.6\,nm}=4.89\,eV\]                         
    \[K{{E}_{\max }}=(4.89-3.82)\,eV=1.077\,eV\]
    \[\frac{1}{2}m{{v}^{2}}=1.077\times 1.6\times {{10}^{-19}}\]
    \[v=\sqrt{\frac{2\times 1.077\times 1.6\times {{10}^{-19}}}{9.1\times {{10}^{-31}}}}\]
    \[v=0.6\times {{10}^{6}}\,m/s\]


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