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JEE Main & Advanced Physics Ray Optics Question Bank Refraction at Curved Surface

  • question_answer
    A candle placed 25 cm from a lens, forms an image on a screen placed 75 cm on the other end of the lens.  The focal length and type of the lens should be        [KCET 2000]

    A) + 18.75 cm and convex lens

    B) - 18.75 cm and concave lens

    C) + 20.25 cm and convex lens

    D) - 20.25 cm and concave lens

    Correct Answer: A

    Solution :

    \[u=-\,25\,\,cm,\,v=+\,75\,cm\]           \[\Rightarrow \]\[\frac{1}{f}=\frac{1}{+75}-\frac{1}{-25}\Rightarrow f=+18.75\]cm ; convex lens.


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