A point source of light is 245.0 cm below the surface of a body of water. Find the diameter of the circle at the surface through which light emerges from the water. Can someone give me a push start as to how to approach this problem? I can't figure it out for the life of me. I know that v=c/n, and using 1.33 at the index of refraction of water, I can find the velocity of the light as it reaches the surface is 2.3E8m/s. The point source will emit light isotropically in all directions, and I have the distance to the surface... but for the life of me I can't find how to relate this to the diameter of the circle it will leave on the surface.