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JEE Main & Advanced Physics Question Bank Human Eye and Lens Camera

  • question_answer
    A person can see clearly only upto a distance of 25 cm. He wants to read a book placed at a distance of 50 cm. What kind of lens does he require for his spectacles and what must be its power                                         [MP PMT 1992]

    A)            Concave, ? 1.0 D                 

    B)            Convex, + 1.5 D

    C)            Concave, ? 2.0 D                 

    D)            Convex, + 2.0 D

    Correct Answer: C

    Solution :

                       For correcting myopia, concave lens is used and for lens. u = wants to see \[=-\,50\,cm\] v = can see \[=-\,25\,cm\]                    From \[\frac{1}{f}=\frac{1}{v}-\frac{1}{u}\]\[\Rightarrow \frac{1}{f}=\frac{1}{-25}-\frac{1}{(-50)}\]\[\Rightarrow f=-\,50\,cm\]            So power \[P=\frac{100}{f}=\frac{100}{-50}=-\,2\,D\]


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