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

  • question_answer
    The focal length of lens of refractive index 1.5 in air is 30 cm.  When it is immersed in a liquid of refractive index \[\frac{4}{3}\], then its focal length in liquid will be  [BHU 2002]

    A)            30 cm                                      

    B)            60 cm

    C)            120 cm                                    

    D)            240 cm

    Correct Answer: C

    Solution :

               By using\[\frac{{{f}_{l}}}{{{f}_{a}}}=\frac{{{(}_{a}}{{\mu }_{g}}-1)}{{{(}_{l}}{{\mu }_{g}}-1)}\Rightarrow {{f}_{w}}=4{{f}_{a}}=4\times 30\]=120 cm.


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