NEET Sample Paper NEET Sample Test Paper-73

  • question_answer
    A photon of energy 4 eV is incident on a metal surface whose work function is 2 eV. The minimum reverse potential to be applied for stopping the emission of electrons is

    A) 2 V                              

    B) 4 V

    C) 6 V                              

    D) 8 V

    Correct Answer: A

    Solution :

    Kinetic energy of photoelectron is \[e{{V}_{0}}\,\,where\,\,{{V}_{0}}\] is stopping potential. From Einstein?s photoelectric equation \[{{E}_{k}}=\frac{1}{2}m{{\nu }^{2}}_{\max }=h\nu -W\] where \[{{E}_{k}}\] is the maximum kinetic energy of electron, v is the frequency and W is the work function. \[\therefore \,\,\,\,\,\,\,\,\frac{1}{2}m{{\nu }^{2}}_{\max }=4\,eV-2\,eV=2\,eV\] \[but\,\,\,\,\,\,\,\,\frac{1}{2}m{{\nu }^{2}}_{\max }\,=\,e\,{{V}_{0}}\] where \[{{V}_{0}}\] is stopping potential. Thus, \[{{\operatorname{eV}}_{0}} = 2 eV\] \[\Rightarrow \,\,\,{{V}_{0}}=2\,V\]


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