Punjab Medical Punjab - MET Solved Paper-2011

  • question_answer
    In a photoelectric experiment, the. Stopping potential for incident light of wavelength \[4000\,\,\overset{\text{o}}{\mathop{\text{A}}}\,\] is \[2\,V\] . If the wavelength is changed to\[3000\,\,\overset{\text{o}}{\mathop{\text{A}}}\,\], the stopping potential is

    A) \[2\,\,V\]

    B)  less than\[2\,\,V\]

    C)  more than\[2\,\,V\]

    D)  zero

    Correct Answer: C

    Solution :

    When stopping potential is\[V\], then                 \[E=eV-\phi \] or            \[\frac{hc}{\lambda }=eV-\phi \] or            \[eV=\frac{hc}{\lambda }+\phi \] where\[e,\,\,h\]and\[c\]are constants \[\therefore \]  \[V\propto \frac{1}{\lambda }\] Hence, if wavelength decreases, stopping potential will increase. \[\therefore \]  \[\frac{{{V}_{2}}}{{{V}_{1}}}=\frac{{{\lambda }_{1}}}{{{\lambda }_{2}}}=\frac{4000}{3000}\] or            \[{{V}_{2}}=\frac{4}{3}\times 2v=\frac{8}{3}v>2v\]


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