JEE Main & Advanced Sample Paper JEE Main Sample Paper-20

  • question_answer
    In a photoelectric experiment, with light of wavelength \[\lambda ,\]the fastest electron has speed v. If the exciting wavelength is changed to \[3\lambda /4,\] the speed of the fastest emitted electron will become         

    A)  \[v\sqrt{\frac{3}{4}}\]                          

    B)   \[v\sqrt{\frac{4}{3}}\]

    C)  less than \[v\sqrt{\frac{4}{3}}\]

    D)  greater than \[v\sqrt{\frac{4}{3}}\]

    Correct Answer: C

    Solution :

     \[\frac{1}{2}m{{v}^{2}}=\frac{hc}{\lambda }-\phi \] \[\frac{1}{2}m{{v}^{2}}=\frac{hc}{(3\lambda /4)}-\phi =\frac{4hc}{3\lambda }\phi .\] Clearly, \[v'>\sqrt{\frac{4}{3}}v\]


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