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BR Physics Optics Thin Layer Example 10.12b

Started by jw1985
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jw1985

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A thin layer of plastic (n=1.46) coats the surface of a glass plate (n=1.52). When monochromatic light is shined normally onto the plastic from the air above, constructive interference occurs. Destructive interference will occur when the coated glass is immersed in which of the following liquids?

I. water (n=1.33)
II. Carbon Tetrachloride (n=1.46)
III. Benzene (n=1.50)

A. I
B. I and II
C. II and III
D. III

The book says the answer is D. I understand why immersing the glass into benzene would result in only 1 phase flip of 180deg. But why wouldn't II with carbon tetrachloride also be valid?

I would expect it to also work because CCl4, has the same refractive index, therefore it does not cause a phase flip or different refractive angles. So, can't I expect there only to be one phase flip between the plastic and class interface?

Thanks in Advance!