BHU PMT BHU PMT (Screening) Solved Paper-2011

  • question_answer
    The threshold wavelength for a photo-sensitive surface is \[6000\,\overset{\text{o}}{\mathop{\text{A}}}\,\] and the wavelength of incident light is \[5000\,\overset{\text{o}}{\mathop{\text{A}}}\,\]. Then the maximum energy of emitted electrons would be

    A)  0.041 eV             

    B)  0.41 eV

    C)   4.1 eV                                

    D)  41 eV

    Correct Answer: B

    Solution :

                     \[{{E}_{k}}=\frac{hc}{\lambda }-\frac{hc}{{{\lambda }_{0}}}\] \[{{E}_{k}}=\frac{4.14\times {{10}^{-15}}\times 3\times {{10}^{8}}}{{{10}^{-7}}}\left( \frac{1}{5}-\frac{1}{6} \right)\] \[{{E}_{k}}=4.14\times {{10}^{-15}}\times 3\times {{10}^{15}}\left( \frac{6-5}{30} \right)\] \[{{E}_{k}}=4.14\times 3\times \frac{1}{30}\] \[{{E}_{k}}\approx 0.14eV\]


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