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

  • question_answer
    A convex lens has 9 cm focal length and a concave lens has -18 cm focal length.  The focal length of the combination in contact will be                                                                [RPMT 1999]             

    A) 9 cm                                         

    B) - 18 cm

    C) - 9 cm                                     

    D) 18 cm

    Correct Answer: D

    Solution :

    \[\frac{1}{F}=\frac{1}{{{f}_{1}}}+\frac{1}{{{f}_{2}}}\Rightarrow \frac{1}{F}=\frac{1}{(+18)}\Rightarrow F=18\,cm\]


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