JEE Main & Advanced Sample Paper JEE Main - Mock Test - 42

  • question_answer
    All electrons ejected from a surface by incident light of wavelength \[200\,nm\] can be stopped before travelling \[1\,m\] in the direction of uniform electric field of\[4N/C\]. The work function of the surface is

    A) \[4\,eV\]            

    B)        \[6.2\,eV\] 

    C) \[2\,eV\]            

    D)        \[2.2\,eV\]

    Correct Answer: D

    Solution :

    The electron ejected with maximum speed \[{{v}_{\max }}\] are stopped by electric field \[E\text{ }=4N/C\]after travelling a distance \[d=1m\] \[\frac{1}{2}mv_{\max }^{2}=eEd=4eV\] The energy of incident photon \[=\frac{1240}{200}=6.2eV\] From equation of photo electric effect \[\frac{1}{2}mv_{\max }^{2}=hv-{{\phi }_{0}}\] \[\therefore \,\,{{\phi }_{0}}=6.2-4=2.2eV\]


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