In water at a depth H there is a point source of light of strength I, and on the same vertical line at a height H above the water surface there is a round screen with a radius a significantly less than H. Find the total luminous flux incident on the screen, taking into account that the energy the reflection coefficient for rays normally incident on the interface is equal to R. The refractive index of water is equal to n. Note. Take advantage of the fact that at small angles sin a = tan a.

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