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NEET Sample Paper NEET Sample Test Paper-70

  • question_answer
    If light of wavelength \[{{\lambda }_{1}}\] is allowed to fall on a metal, then kinetic energy of photoelectrons emitted is\[{{E}_{1}}\]. If wavelength of light changes to \[{{\lambda }_{2}}\], then kinetic energy of electrons changes to \[{{E}_{2}}\], then work function of the metal is        

    A) \[\frac{{{E}_{1}}{{E}_{2}}({{\lambda }_{1}}-{{\lambda }_{2}})}{{{\lambda }_{1}}{{\lambda }_{2}}}\]       

    B) \[\frac{{{E}_{1}}{{\lambda }_{1}}-{{E}_{2}}{{\lambda }_{2}}}{({{\lambda }_{1}}-{{\lambda }_{2}})}\]

    C) \[\frac{{{E}_{1}}{{\lambda }_{1}}-{{E}_{2}}{{\lambda }_{2}}}{({{\lambda }_{2}}-{{\lambda }_{1}})}\]                  

    D) \[\frac{{{\lambda }_{1}}{{\lambda }_{2}}{{E}_{1}}{{E}_{2}}}{({{\lambda }_{2}}-{{\lambda }_{1}})}\]

    Correct Answer: C

    Solution :

    \[E={{W}_{0}}+{{K}_{\max }}\] \[\Rightarrow \,\,\,\,\,\,\frac{hc}{{{\lambda }_{1}}}\,={{W}_{0}}+{{E}_{1}}\,and\,\,\frac{hc}{{{\lambda }_{2}}}\,=\,{{W}_{0}}+E2\] \[\Rightarrow \,\,\,\,\,\,hc={{W}_{0}}{{\lambda }_{1}}+{{E}_{1}}{{\lambda }_{1}}\,and\,\,hc={{W}_{0}}{{\lambda }_{2}}+{{E}_{2}}{{\lambda }_{2}}\] \[\Rightarrow \,\,\,\,\,\,{{W}_{0}}{{\lambda }_{1}}+{{E}_{1}}{{\lambda }_{1}}\,\,=\,\,hc={{W}_{0}}{{\lambda }_{2}}+{{E}_{2}}{{\lambda }_{2}}\] \[\Rightarrow \,\,\,\,\,\,{{W}_{0}}=\frac{{{E}_{1}}{{\lambda }_{1}}-{{E}_{2}}{{\lambda }_{2}}}{({{\lambda }_{2}}-{{\lambda }_{1}})}\]


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