A point source of power 4W is placed 1m below the free surface of liquid whose refractive index is 2√3Find the rate of transfer of energy (in watt) from the liquid surface to air. Ignore any absorption or scattering of light energy.
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The light escape is confined within a cone of apex angle 2θcwhere θcis the critical angle. Imagine a sphere with source of light as its centre and the surface area abc is A. Here A = ∫θc02πR2sinθdθ=2πR2(1−cosθc) = πR2[∴θc=sin−1(√32=60∘)]∴Power transfer = P ×A4πR2 = 4 ×14 = 1 W