Mike has installed a light bulb at the bottom of his water pool. At night, he turns on the light. He observes that the light produces a bright circle with a radius
of one meter on the water surface. The rest of the surface is completely dark.
The reason is that the rest of the light rays go under total internal reflection and
do not get out of the water. How deep is the pool? The refraction index of water
is n=1.3.