A thin film surrounded by air has an index of refraction of 1.4. a region of the film appears bright blue (a = 400 nm) when white light is incident perpendicul

A thin film surrounded by air has an index of refraction of 1.4. A region of the film appears bright blue (A = 400 nm) when white light is incident perpendicular to the surface. What might be the minimum thickness of the film? A. 140 nm B. 280 nm C. 420 nm D. 70 nm