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

  • question_answer
    A person who can see things most clearly at a distance of 10 cm. Requires spectacles to enable to him to see clearly things at a distance of 30 cm. What should be the focal length of the spectacles              [BHU 2003; CPMT 2004; PM PMT 2005]

    A)            15 cm (Concave)                 

    B)            15 cm (Convex)

    C)            10 cm                                      

    D)            0

    Correct Answer: A

    Solution :

                       For lens u = wants to see = ? 30 cm and v = can see = ? 10 cm \[\therefore \frac{1}{f}=\frac{1}{v}-\frac{1}{u}\]\[=\frac{1}{-10}-\frac{1}{(-30)}\]\[\Rightarrow f=-\,15\,cm\]


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