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

  • question_answer
    A convex lens is in contact with concave lens. The magnitude of the ratio of their focal length is 2/3. Their equivalent focal length is 30 cm. What are their individual focal lengths                                    [IIT-JEE (Screening) 2005]

    A)            ? 75, 50                                   

    B)            ? 10, 15

    C)            75, 50                                      

    D)            ? 15, 10

    Correct Answer: D

    Solution :

                       \[\frac{{{f}_{1}}}{{{f}_{2}}}=\frac{2}{3}\]                            .....(i) \[\frac{1}{{{f}_{1}}}-\frac{1}{{{f}_{2}}}=\frac{1}{30}\]                      .....(ii) Solving equation (i) and (ii) \[{{f}_{2}}=-\,15\,cm\]                 (Concave) \[{{f}_{1}}=10\,cm\]                      (Convex)


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