Chapter 32.1, Problem 32.1GI

Laser light is split into two beams, one of which is sent on a path that takes it through a slab of glass, where light's speed is about two-thirds of what it is in air. The other beam travels an identical-length path, entirely in air. Which of the following describes the interference that occurs when the beams are recombined? (a) It's constructive; (b) it’s destructive; (c) it could be constructive, destructive, or in between, depending on the thickness of the glass slab; (d) there is no interference.