p36_041

# p36_041 - 41 Light reected from the upper oil surface(in...

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41. Light reﬂected from the upper oil surface (in contact with air) changes phase by π rad. Light reﬂected from the lower surface (in contact with glass) changes phase by π rad if the index of refraction of the oil is less than that of the glass and does not change phase if the index of refraction of the oil is greater than that of the glass. First, suppose the index of refraction of the oil is greater than the index of refraction of the glass. The condition for fully destructive interference is 2 n o d = ,whe re d is the thickness of the oil ±lm, n o is the index of refraction of the oil, λ is the wavelength in vacuum, and m is an integer. For the shorter wavelength, 2 n o d = m 1 λ 1 and for the longer, 2 n o d = m 2 λ 2 .S i n c e λ 1 is less than λ 2 , m 1 is greater than m 2 , and since fully destructive interference does not occur for any wavelengths between, m
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