A drop of oil (n = 1.4) is on a glass (n = 1.5) sheet and is observed from directly above by reflected white light. A number of circular constructive interference bands are observed for each colour in the visible spectrum. Approximately how thick is the oil film where one observes the third blue band from the outside edge of the drop. The wavelength of blue light may be taken to be λ_b = 450 nm.
[Figure: Diagram showing observer above oil drop on glass with labeled air, oil, and glass layers]
(a) 482 nm
(b) 675 nm
(c) 1125 nm
(d) 1350 nm