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JEE Main & Advanced Physics Ray Optics Sample Paper Topic Test - Refraction of Light Through Plane Surfaces

  • question_answer
    A point source of light is placed at a distance h below the surface of a large deep lake. What is the percentage of light energy that escapes directly from the water surface if \[\mu \] of water \[=\frac{4}{3}\]?

    A) 50%

    B) 25%

    C) 20%

    D) 17%

    Correct Answer: D

    Solution :

    [d] The solid angle subtended by area shown by the shaded portion in
    \[2\pi \,(1-\cos \,C)\]
    So, % going out \[=\frac{2\pi (1-\cos C)}{4\pi }\times 100\]
    \[=\frac{1}{2}\,(1-\cos C)\times 100=17%\]
    C = critical angle.


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