AMU Medical AMU Solved Paper-2000

  • question_answer
    Find the number of photon emitted per second by a 25 W source of monochromatic light of wavelength \[6600\,\overset{\text{o}}{\mathop{\text{A}}}\,\]. What is the photoelectric current assuming 3% efficiency for photoelectric effect ?

    A)  \[\frac{25}{3}\times {{10}^{19}}J,0.4\,A\]            

    B)  \[\frac{25}{4}\times {{10}^{19}}J,6.2\,A\]

    C)  \[\frac{25}{2}\times {{10}^{19}}J,0.8\,A\]            

    D)  None of the above

    Correct Answer: A

    Solution :

                     From Einsteins relation, the energy of photon of wavelength \[(\lambda )\] is                 \[E=\frac{hc}{\lambda }\] Given,   \[h=6.6\times {{10}^{-34}}Js\],                 \[c=3\times {{10}^{8}}m/s\],                 \[\lambda =6600\,\overset{o}{\mathop{A}}\,\]                 \[\lambda =6600\times {{10}^{-10}}m\] \[\therefore \]  \[E=\frac{6.6\times {{10}^{-34}}\times 3\times {{10}^{8}}}{6600\times {{10}^{-10}}}\]                 \[=3\times {{10}^{-19}}J\] Number of photons emitted per second by 25 W source is                 \[n=\frac{25\,W\times 1\,\,s}{3\times {{10}^{-19}}}\]                 \[=\frac{25}{3}\times {{10}^{19}}\] and        \[I=ne\]                 \[=\frac{3}{100}\times \frac{25}{3}\times {{10}^{19}}\times 1.6\times {{10}^{-19}}\]                 = 0.4 A


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