AFMC AFMC Solved Paper-2010

  • question_answer
    The threshold frequency for a metallic surface corresponds to an energy of 6.2 eV and the stopping potential for a radiation incident on this surface is 5 V. The incident radiation lies in

    A) ultra violet region           

    B) infrared region

    C) visible region                                    

    D) X - ray region

    Correct Answer: A

    Solution :

    From Einstein's photoelectric equation \[hv=h{{v}_{0}}+e{{V}_{0}}\]     \[=6.2+5=11.2\,\,eV\] \[\Rightarrow \]  \[\frac{hc}{\lambda }=11.2\,eV\]or      \[\lambda =\frac{hc}{11.2\,eV}\] \[=\frac{6.6\times {{10}^{-34}}\times 3.0\times {{10}^{8}}}{11.2\times 1.6\times {{10}^{-19}}}\] \[=1.1049\times {{10}^{-7}}\] \[=1104.9\overset{\text{o}}{\mathop{\text{A}}}\,\] This incident radiation lies in ultra violet region,


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