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

  • question_answer
    The distance between an object and the screen is 100 cm. A lens produces an image on the screen when placed at either of the positions 40 cm apart. The power of the lens is [SCRA 1994]

    A)            \[\approx \] 3 dioptres    

    B)            \[\approx \] 5 dioptres

    C)            \[\approx \] 7 diopters    

    D)            \[\approx \] 9 diopters

    Correct Answer: B

    Solution :

                       \[f=\frac{{{D}^{2}}-{{x}^{2}}}{4D}\] (Focal length by displacement method)                    \[\Rightarrow f=\frac{{{(100)}^{2}}-{{(40)}^{2}}}{4\times 40}=21\ cm\]            \[\therefore P=\frac{100}{f}=\frac{100}{21}\approx 5\,D\]


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