Q. A thin film of oil ( n = 1.15) is located on smooth, wet pavement. When viewe

Question

Q. A thin film of oil (n = 1.15) is located on smooth, wet pavement. When viewedfrom a direction perpendicular to the pavement, the film reflectsmost strongly red light at 640 nm and reflects no light at569 nm. What is the minimum thickness ofthe oil film?
I know that there are total two phase reversals, but how do we solve for thickness? Q. A thin film of oil (n = 1.15) is located on smooth, wet pavement. When viewedfrom a direction perpendicular to the pavement, the film reflectsmost strongly red light at 640 nm and reflects no light at569 nm. What is the minimum thickness ofthe oil film?
I know that there are total two phase reversals, but how do we solve for thickness?

Explanation / Answer

    in the given problem since 1 < 1.15 < 1.33light reflected both from the top and from the bottom surface ofthe oil suffers     phase reversal     for constructive interference we requirethat     2 t = m cons / n     for destructive interference we require that     2 t = [m + (1 / 2)] des / n      cons /des = 1 + (1 / 2 m)                        = 640 nm / 569 nm     and m = 2     solve for t

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