A scuba diver is $1\mathrm{.}2$ m beneath the surface of a still pond of water. At what angle relative to the normal at the surface must the diver shine a beam of light toward the surface in order for a person on a distant bank to be able to see it$?$ The index of refraction for water is $1\mathrm{.}33.$ Answer: $49$

Hint... The angle of refraction is $90$ so you are being asked to find the critical angle.