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VMMC VMMC Medical Solved Paper-2011

  • question_answer
    A glass convex lens \[(\mu =1.5)\] has a focal length of 8 cm when placed in air. What would be the focal length of lens when it is immersed in water \[({{\mu }_{w}}\,=4\,/3)\]?

    A)  2 m

    B)                                         4 cm                     

    C)  16 cm                  

    D)         32 cm

    Correct Answer: D

    Solution :

                            Let focal length becomes \[{{f}_{w}}\]on inserting the lens in water, then using relation \[\frac{{{f}_{w}}}{{{f}_{a}}}=\frac{({{\mu }_{g}}-1)}{\left( \frac{{{\mu }_{g}}}{{{\mu }_{w}}}-1 \right)}\] or            \[\frac{{{f}_{w}}}{8}=\frac{(1.5-1)}{\left( \frac{1.5}{4/3}-1 \right)}\] Hence, \[{{f}_{w}}=32\,cm\]


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