Question

A fish lives at the bottom of a lake 10m deep filled with water whose index of refraction 1.52.

a) At what angle relative to the normal must the fish look up towards the surface of the water in order to see a fisherman who is sitting on a distant shore?

b)What is the closest that another fish living at the bottom of the lake can approach in order that the first fish can see it by looking towards the surface?

Answer 1

Part A) To see the man angle of rectration for the man must be 90⁰ i.e. angle of incidence must be equal to critical angle.

Using Snell's law

Part b) for the other fish to there must be total internal reflection, let it be at a distance d from the first fish. From the right angled triangle