CET Karnataka Medical CET - Karnataka Medical Solved Paper-2008

  • question_answer
    When a piece of metal is illuminated by a monochromatic light of wavelength X, then stopping potential is\[3{{V}_{s}}\]b. When same surface is illuminated by light of wavelength 2/1, then stopping potential becomes\[{{V}_{s}}\]. The value of threshold wavelength for photoelectric emission will be

    A)  \[4\lambda \]

    B)  \[8\lambda \]

    C)  \[\frac{4}{3}\lambda \]

    D)  \[6\lambda \]

    Correct Answer: A

    Solution :

    According to Einsteins photoelectric equation \[eV=hc\left[ \frac{1}{\lambda }-\frac{1}{{{\lambda }_{0}}} \right]\] Ist case \[3e{{V}_{s}}=hc\left[ \frac{1}{\lambda }-\frac{1}{{{\lambda }_{0}}} \right]\] ?(i) lInd case \[e{{V}_{s}}=hc\left[ \frac{1}{2\lambda }-\frac{1}{{{\lambda }_{0}}} \right]\] ...(ii) Dividing Eq. (i) by Eq. (ii), we get\[{{\lambda }_{0}}=4\lambda \]


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