Punjab Medical Punjab - MET Solved Paper-2008

  • question_answer In Ramsden eyepiece, the two planoconvex lenses each of focal length \[f\] are separated by a distance\[12cm\]. The equivalent focal length (in \[cm\]) of the eyepiece is

    A)  10.5                                      

    B)  12.0

    C)  13.5                                      

    D)  15.5

    Correct Answer: C

    Solution :

    \[d=\frac{2f}{3}\] or            \[f=\frac{3d}{2}=\frac{3\times 12}{2}=18cm\] Equivalent focal length is \[f=\frac{{{f}_{1}}{{f}_{2}}}{{{f}_{1}}+{{f}_{2}}}=\frac{18\times 18}{18+18}+\frac{18}{4}\]      \[=9+4.5\]      \[=13.5\,\,cm\]

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