1. The problem statement, all variables and given/known data Green light is shone onto two soap films. An observer looking down at the soap films sees that soap film X appears uniformly green while soap film Y has green and black bands. If air is the medium on either side of the soap film, the best explanation of this pattern is that: A) film X has a thickness much less than λ and film Y has a thickness of 1/4 λ B) film X has a thickness of 1/2 λ and film Y has a thickness of 1/4 λ C) film X has a thickness of 1/4 λ and film Y has a thickness of 1/2 λ D) film X has consistent thickness throughout whereas film Y has variable thickness E) film X has variable thickness whereas film Y has consistent thickness throughout 2. Relevant equations None given 3. The attempt at a solution Because film X appears uniformly green, we know that it is of a consistent thickness. Therefore, the answer is not (E). The answer is also not (C), because it would cancel due to destructive interference. I'm leaning towards either (B) or (D), but I would like clarification on (A)... I don't understand what "much less than λ" means in the context of the question.