12th Class Physics Sample Paper Physics Sample Paper-9

  • question_answer
    In a plot of photoelectric current versus anode potential, how does
    (i) the saturation current vary with anode potential for incident radiations of different frequencies but same intensity?
    (ii) the stopping potential vary for incident radiations of different intensities but same frequency?
    (iii) photoelectric current vary for different intensities but same frequency of incident radiations?
    Justify your answer in each case.


    (i) In photoelectric effect, the saturation current does not vary with anode potential for incident radiations of different frequencies, but same intensity. The reason is that saturation current depends only on intensity of incident radiation because a single photon can eject a single electron, however large the frequency of radiations may be.
    (ii) According to the Einstein's photoelectric equation, the stopping potential \[({{V}_{0}})\] is given by
                \[e{{V}_{0}}=hv-W\]  or \[{{V}_{0}}=\frac{hv}{e}-\frac{W}{e}\]
    Obviously, stopping potential is independent of intensity provided frequency v remains unchanged. i.e. stopping potential does not vary with intensity of incident radiations.
    (iii) Photoelectric current increases with increase of intensity because increase in intensity of radiations means increase in number of incident photons. As, one photon ejects one electron, increase in intensity causes increase in photoelectric current.

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