Light of Wave Length L Is Incident on Two Thin

Multiple Choice

Light of wave length l is incident on two thin films that are in contact and surrounded by air. The top layer is λ/4 thick and has an index of refraction of 1.33. The bottom layer is λ/2 thick and has an index of refraction of 1.50. At normal incidence, the reflected rays that are in phase with each other are

A) 1 and 2.
B) 1 and 3.
C) 2 and 3.
D) 1, 2, and 3.
E) None of these is correct.