> Q. A disc is placed on a surface of pond which has refractive index 5/3. A source of light is placed 4 m below the surface of liquid. The minimum radius of disc needed so that light is not coming out is – LIVE ANSWER TODAY

Q. A disc is placed on a surface of pond which has refractive index 5/3. A source of light is placed 4 m below the surface of liquid. The minimum radius of disc needed so that light is not coming out is

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A disc is placed on a surface of pond which has refractive index 5/3. A source of light is placed 4 m below the surface of liquid. The minimum radius of disc needed so that light is not coming out is

Solution:

$theta $ is the critical angle.

$therefore , , , , theta = sin ^{-1} (1/ mu ) = sin ^{-1} (3/5)$

or $ , , , sin theta = 3/5 $

$ therefore , , , tan theta = 3/4 = r/4 , , or , , r=3 m $

Solution Image

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