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MGIMS WARDHA MGIMS WARDHA Solved Paper-2012

  • question_answer
    If focal length of convex lens is 9 cm and that of a concave lens is\[-18\text{ }cm,\]then focal length of combination is

    A)  \[+9\text{ }cm\]                             

    B)  \[-18\text{ }cm\]

    C)  \[-9cm\]                             

    D)  \[+18cm\]

    Correct Answer: D

    Solution :

                    Focal length of combination \[\frac{1}{F}=\frac{1}{{{F}_{1}}}+\frac{1}{{{F}_{2}}}\] \[=\frac{1}{9}-\frac{1}{18}\] \[=\frac{2-1}{18}=\frac{1}{18}\] \[F=+18\,cm\]                  


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