JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2011

  • question_answer
        Ultraviolet light of wavelength 350 nm and intensity\[1.00\text{ }W{{m}^{-2}}\]is incident on a potassium surface. If 0.5% of the photons participate in ejecting the photoelectrons, how many photo electrons, are emitted per second, if the potassium surface has an area of\[1\text{ }c{{m}^{2}}\]?

    A) \[1.76\times {{10}^{18}}\]photoelectrons/s

    B)  \[1.76\times {{10}^{14}}\]photoelectrons/s

    C) \[8.8\times {{10}^{11}}\]photoelectrons/s

    D)  The value of work function is required to complete   the   value   of   emitted photoelectrons/s

    Correct Answer: C

    Solution :

                    Energy of photon, \[E=\frac{hc}{\lambda }\]                 \[=\frac{1242}{350}eV=3.55\,eV\]                 \[=5.68\times {{10}^{-19}}J\] Let n photons, per unit area per unit time are reaching the potassium surface, then                 \[n=\frac{1.00}{5.68\times {{10}^{-19}}}\] \[=1.76\times {{10}^{18}}\] So, number of photons received by potassium surface per unit time is, \[n\times \] Area of potassium surface \[=1.76\times {{10}^{18}}\times 1\times {{10}^{-4}}\] \[=1.76\times {{10}^{14}}\] Required number of photoelectrons emitted per unit time                 \[=1.76\times {{10}^{14}}\times \frac{0.5}{100}\]                 \[=8.8\times {{10}^{11}}\]


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