Chapter 7.4, Problem 58E

Total Internal Reflection When light passes from a more dense to a less dense medium-from glass to air, for example-the angle of refraction predicted by Snell’s Law (see exercise 57 )can be $90°$ or large. In this case the light beam is actually reflected Bach into the denser medium. This phenomenon, called total internal reflection, is the principal behind optics. Set ${\theta }_2=90°$ in Snell’s Law, and solve for ${\theta }_1$ to determine the critical angle of incidence at which total internal reflection begins to occur when light passes from glass to air. (Note that the index of refraction from glass to air is reciprocal of the index from air to glass.)