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

  • question_answer
    An object placed 10 cm in front of a lens has an image 20 cm behind the lens. What is the power of the lens (in dioptres)  [MP PMT 1995]

    A)            1.5 

    B)            3.0

    C)            ? 15.0                                      

    D)            + 15.0

    Correct Answer: D

    Solution :

                       \[u=-10\ cm,\ \ v=20\ cm\]                    \[\frac{1}{f}=\frac{1}{v}-\frac{1}{u}=\frac{1}{20}-\left( -\frac{1}{10} \right)=\frac{3}{20}\Rightarrow f=\frac{20}{3}\ cm\]            Now \[P=\frac{100}{f}=\frac{100}{20/3}=+\ 15\ D\]


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