Uttarakhand PMT Uttarakhand PMT Solved Paper-2009

  • question_answer
     The work function of a substance is 4.0 eV. The longest wavelength of light that can cause photoelectron emission from this substance is approximately

    A)  540 nm      

    B)  400 nm

    C)  310 nm       

    D)  220 nm

    Correct Answer: C

    Solution :

     The minimum energy of incident radiations, required to eject the electrons from metallic surface is defined as work function of that surface. \[{{W}_{0}}=h{{v}_{0}}=\frac{hc}{{{\lambda }_{0}}}\] where\[{{\lambda }_{0}}=\]threshold wavelength. Work function in electron volt\[{{W}_{0}}(eV)\] \[{{W}_{0}}=\frac{12400}{{{\lambda }_{0}}(\overset{o}{\mathop{\text{A}}}\,)}eV\] \[\therefore \] \[4.0=\frac{12400}{{{\lambda }_{0}}}\] \[\Rightarrow \] \[{{\lambda }_{0}}=310\,nm\]


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