lorenz0
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- Homework Statement
- A soap water film ## n = 1.46 ## with a thickness of ## d = 10^{-6} m ## is placed on a glass plate with a refractive index of ## n = 1.6.## The film is perpendicularly illuminated by green light with a wavelength of ## 566 nm.## What is the optical path difference between the rays reflected from the two sides of the film, expressed in terms of the wavelength of the light inside the film?
- Relevant Equations
- ##\Delta=\sum_i n_i d_i ##
The ray that is reflected at the air-soap interface has an optical path length of ##lambda_{soap}/2##, while the one refracted in the soap has an optical path length of ##2 n_{soap} d+\frac{lambda_{glass}}{2}## due to its traversing the soap film and also reflecting on the soap-glass interface. Thus the optical path difference between the two rays is ##\Delta=2 n_{soap} d+\frac{lambda_{glass}}{2}-\frac{lambda_{soap}}{2}## which can also be written as ##\Delta=\frac{2 n_{soap} d+\frac{lambda_{glass}}{2}-\frac{lambda_{soap}}{2}}{lambda_{soap}}lambda_{soap}\approx 7.49 lambda_{soap}##, which according to the stated solution is wrong, since it should be ##5.16 lambda_{soap}.## I would be grateful if someone could tell me where I am going wrong. Thanks.
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