JEE Main & Advanced JEE Main Solved Paper-2016

  • question_answer
    Radiation of wavelength \[\lambda ,\]is incident on a photocell. The fastest emitted electron has speed v. If the wavelength of changed to\[\frac{3\lambda }{4},\] the speed of the fastest emitted electron will be :- [JEE Main Solved Paper-2016 ]

    A) \[=v{{\left( \frac{3}{5} \right)}^{1/2}}\] 

    B) \[>v{{\left( \frac{4}{3} \right)}^{1/2}}\]

    C) \[<v{{\left( \frac{4}{3} \right)}^{1/2}}\]                 

    D) \[=v{{\left( \frac{4}{3} \right)}^{1/2}}\]

    Correct Answer: B

    Solution :

                    \[E={{(KE)}_{\max }}+f\]                 \[\left[ \frac{hc}{\lambda }={{(KE)}_{\max }}+\phi  \right]\]                                       ?(1)                 \[\frac{4}{3}\frac{hc}{\lambda }=\left( \frac{4}{3}K{{E}_{\max }}+\frac{\phi }{3} \right)+\phi \] \[K{{E}_{\max }}\]for fastest emitted electrum\[=\frac{1}{2}mV{{'}^{2}}+\phi \] \[=\frac{1}{2}V{{'}^{2}}\frac{4}{3}\left( \frac{1}{2}m{{V}^{2}} \right)+\frac{\phi }{3}\]\[\]


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