Punjab Medical Punjab - MET Solved Paper-2010

  • question_answer
    A thin convergent glass lens \[\mu =1.5\] has a power of\[+5.0D\]. When this lens is immersed in a liquid of refractive index \[{{\mu }_{1}}\] it acts as a diverging lens of focal length\[100cm\]. The value of\[{{\mu }_{l}}\]should be

    A) \[\frac{3}{2}\]                                   

    B) \[\frac{4}{3}\]

    C) \[\frac{5}{3}\]                                   

    D) \[2\]

    Correct Answer: C

    Solution :

    When the lens in air, we have                 \[{{P}_{a}}=\frac{1}{{{f}_{a}}}=\frac{{{\mu }_{g}}-{{\mu }_{a}}}{{{\mu }_{a}}}\left[ \frac{1}{{{R}_{1}}}-\frac{1}{{{R}_{2}}} \right]\] When the lens is in liquid, we have                 \[{{P}_{l}}=\frac{1}{{{f}_{l}}}=\frac{{{\mu }_{g}}-{{\mu }_{l}}}{{{\mu }_{l}}}\left[ \frac{1}{{{R}_{1}}}-\frac{1}{{{R}_{2}}} \right]\] Here,\[{{P}_{a}}=5,\,\,{{P}_{l}}=-1,\,\,{{\mu }_{a}}=1,\,\,{{\mu }_{g}}=1.5\] On solving, we get,\[{{\mu }_{l}}=\frac{5}{3}\]


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