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MGIMS WARDHA MGIMS WARDHA Solved Paper-2003

  • question_answer
    A convex lens of focal length 12 cm is made up of a glass of refractive index \[\frac{3}{2.}\]When it is immersed in a liquid of refractive index\[\frac{5}{4.}\] its focal length will be :

    A) 15 cm                                   

    B) 6 cm

    C) 30 cm                                   

    D) 24 cm

    Correct Answer: C

    Solution :

    Here: \[_{a}{{n}_{g}}=\frac{3}{2}{{,}_{a}}{{n}_{\omega }}=\frac{5}{4},{{f}_{1}}=12\,cm\] \[\therefore \]  \[_{\omega }{{n}_{g}}=\frac{_{a}{{n}_{g}}}{_{a}{{n}_{\omega }}}=\frac{3/2}{5/4}=\frac{6}{4}\]                 \[\frac{{{f}_{2}}}{{{f}_{1}}}=\frac{{{(}_{a}}{{n}_{g}}-1)}{{{(}_{a}}{{n}_{\omega }}-1)}\] Or           \[\frac{{{f}_{2}}}{12}=\frac{(3/2-1)}{(6/5-1)}\] Or           \[{{f}_{2}}=\left( \frac{1/2}{1/5} \right)\times 12\] Hence, \[{{f}_{2}}=30\text{ }cm\]


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