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JIPMER Jipmer Medical Solved Paper-2005

  • question_answer
    A person who can see things most clearly at a distance of 10 cm, requires spectacles to enable to see clearly things at a distance of 30 cm. What should be the focal length of the spectacles?

    A)  15 cm (Concave)             

    B)  15 cm (Convex)

    C)         10 cm                  

    D)         0

    Correct Answer: A

    Solution :

    A concave lens is required by the person so that the lens forms the image of object distant 30 cm, at 10 cm it means \[u=-\,30\,cm,\,\]\[\upsilon =-10\,cm\] \[\frac{1}{f}=\frac{1}{\upsilon }-\frac{1}{u}\]      \[=\frac{1}{-10}-\frac{1}{-\,30}\]      \[=-\frac{2}{30}\] or                            \[\frac{1}{f}=\frac{-1}{15}\] so                           \[f=-15\,cm\] Minus sign signifies that lens used is concave


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