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Punjab Medical Punjab - MET Solved Paper-2008

  • question_answer
    A diverging meniscus lens of \[1.5\] refractive index has concave surfaces of radii \[3\] and\[4cm.\]The position of the image, if an object is placed \[12cm\] in front of the lens, is

    A) \[7cm\]                               

    B) \[-8cm\]

    C) \[9cm\]                               

    D) \[10cm\]

    Correct Answer: B

    Solution :

    \[\frac{1}{f}=(\mu -1)\left( \frac{1}{{{R}_{1}}}-\frac{1}{{{R}_{2}}} \right)\] For given concave lens,                 \[{{R}_{1}}=-3cm\],         \[{{R}_{2}}=-4cm\] \[\therefore \]  \[\frac{1}{v}-\frac{1}{u}=(\mu -1)\left( \frac{1}{-3}+\frac{1}{4} \right)\] or            \[\frac{1}{v}-\frac{1}{(-12)}=(1.5-1)\left( \frac{-4+3}{12} \right)\] or            \[\frac{1}{v}+\frac{1}{12}=0.5\times \frac{-1}{12}=\frac{-1}{24}\] or            \[\frac{1}{v}=-\frac{1}{24}-\frac{1}{12}=\frac{-1-2}{24}=-\frac{1}{8}\] or            \[v=-8cm\]


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