monochromatic light is normally incident on one face of a prism with a right triangle for a base. the light travels through the prism such that it strikes the hypotenuse of the triangle from inside. the prism is made of glass with an index of refraction ng > ns where ns is the index of the surroundings. what must be the angle of the prism such that the light suffers total internal reflection on the slanted face of the prism?