(3) \([1-\frac{\sqrt{5}}{3}](\frac{1}{2})\)
Fig. shows that only those incident rays from S, that lie within the cone OAA´, emerge out of the upper surface of glass. Also
The area S; from which light emerges out is
The total light, emitted by S, gets spread over the surface of a sphere of radius R, i.e., 4πR2 . Therefore Fraction of total light (emitted by the source S) that passes out of the slab, is