Walker, Halliday & Resnick — Electromagnetic Waves: Problem 31

31 In Fig. 33-44, light initially in material 1 refracts into material 2, crosses that material, and is then incident at the critical angle on the interface between materials 2 and 3. The indexes of refraction are $n_1 = 1.80$, $n_2 = 1.40$, and $n_3 = 1.20$. (a) What is angle $\theta$? (b) If $\theta$ is increased, is there refraction of light into material 3?