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Manipal Medical Manipal Medical Solved Paper-2006

  • 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 :

     Since, the person is not able to see distant objects beyond 10 cm so, he should use concave lens in his spectacles. Concave lens will form the image of object distant 30 cm, at 10 cm it means \[u=-30\text{ }cm,\text{ }v=-10\text{ }cm\] \[\frac{1}{f}=\frac{1}{v}-\frac{1}{u}=\frac{1}{-10}-\frac{1}{-30}=-\frac{2}{30}\] Or \[\frac{1}{f}=-\frac{1}{15}\] So,    \[f=-15cm\] Minus sign signifies that lens used in concave.


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