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

  • question_answer
    The dispersive powers of glasses of lenses used in an achromatic pair are in the ratio 5 : 3. If the focal length of the concave lens is 15 cm, then the nature and focal length of the other lens would be                                            [MP PET 1997]

    A)            Convex, 9 cm                       

    B)            Concave, 9 cm

    C)            Convex, 25 cm                     

    D)            Concave, 25 cm

    Correct Answer: A

    Solution :

               \[\frac{{{\omega }_{1}}}{{{\omega }_{2}}}=-\frac{{{f}_{1}}}{{{f}_{2}}}\Rightarrow \frac{5}{3}=\frac{-(-15)}{{{f}_{2}}}\Rightarrow {{f}_{2}}=9\]\[cm\]


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