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JEE Main & Advanced Physics Ray Optics Question Bank Refraction at Curved Surface

  • question_answer
    A thin convex lens of refractive index 1.5 has a focal length of 15 cm in air. When the lens is placed in liquid of refractive index 4/3 , its focal length will be [CPMT 1974, 77; MP PMT 1992]

    A)            15 cm                                      

    B)            10 cm

    C)            30 cm                                      

    D)            60 cm

    Correct Answer: D

    Solution :

               \[\frac{{{f}_{l}}}{{{f}_{a}}}=\frac{{{(}_{a}}{{\mu }_{g}}-1)}{{{(}_{l}}{{\mu }_{g}}-1)}\]\[\Rightarrow \frac{{{f}_{l}}}{15}=\frac{(1.5-1)}{\left( \frac{1.5}{4/3}-1 \right)}\]\[\Rightarrow {{f}_{l}}=60\,cm\]


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