There is a small source of light at some depth below the surface of water (refractive index $=4 / 3$ ) in a tank of large cross-sectional surface area. Neglecting any reflection from the bottom and absorption by water, percentage of light that emerges out of surface is (nearly) [Use the fact that surface area of a spherical cap of height $h$ and radius of curvature $r$ is $2 \pi \mathrm{rh}$ ]