38. IE •• A light beam traveling upward in a plastic material with an index of refraction of 1.60 is incident on an upper horizontal air interface.

(a) At certain angles of incidence, the light is not transmitted into air. The cause of this is (1) reflection, (2) refraction, (3) total internal reflection. Explain.

(b) If the angle of incidence is 45°, is some of the beam transmitted into air?

(c) Suppose the upper surface of the plastic material is covered with a layer of liquid with an index of refraction of 1.20. What happens in this case?