im having difficulty understanding how light leaves a prism mainly because im not sure about what angles we are talking about when we say angle of refraction/incidence. Lets say for example light hits a triangular prism leg at a 90 degree angle (incidence = 90 deg?) and the prism has index of 1.4 compared to surrounding air's 1.0 using snells law would get an angle of refraction. Now Im getting lost trying to find the angle that it strikes the hypotenuse and the angle that it leaves the prism. how would i use snells law again?