A point source of light is placed at the bottom of a vessel which is filled with water of refractive index to a height h. If a floating opaque disc has to be placed exactly above it so that the source is invisible from above, the radius of

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A point source of light is placed at the bottom of a vessel which is filled with water of refractive index to a height h. If a floating opaque disc has to be placed exactly above it so that the source is invisible from above, the radius of the disc should be-

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Correct answer: B. h ²-1

r should be such that rays beyond it got totally internally reflected For this >C or > C also = 1 C r h²+r² > 1 In limiting case r h ²+ r ² = 1 ving we get = h ²-1

A point source of light is placed at the bottom of a vessel which is filled with water of refractive index to a height h. If a floating opaque disc has to be placed exactly above it so that the source is invisible from above, the radius of the disc should be-

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