RAJASTHAN PMT Rajasthan - PMT Solved Paper-2010

  • question_answer
    Assuming photoemission to take place, the factor by which the maximum velocity of the emitted photoelectrons changes when the wavelength of the incident radiation is increased four times, is

    A)  4                                            

    B)  \[\frac{1}{4}\]

    C)  2                            

    D)         \[\frac{1}{2}\]

    Correct Answer: D

    Solution :

    According to Einsteins equation                 \[\frac{hc}{\lambda }={{W}_{0}}+\frac{1}{2}mv_{\max }^{2}\] Assume \[{{W}_{0}}\] to be negligible in comparison to\[\frac{hc}{\lambda }\]. \[ie,\]    \[v_{\max }^{2}\propto \frac{1}{\lambda }\Rightarrow {{v}_{\max }}\propto \frac{1}{\sqrt{\lambda }}\] On increasing wavelength \[\lambda \] to\[4\lambda ,\,\,{{v}_{\max }}\] becomes half.


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