# Homework Help: Reflected white light, thin transparent coating on glass

1. Apr 17, 2007

### aquabum619

1. The problem statement, all variables and given/known data

Suppose a reflected white light is used to observe a thin transparent coating on glass as the coating material is gradually deposited by evaporation in a vacuum, Describe color changes that might occur during the process of building up the thickness of the coating

2. Relevant equations

3. The attempt at a solution
im not sure

2. Apr 17, 2007

### aquabum619

The interference of waves reflected from the opposite surface of the film would cause a band of colors to be formed in the film.
Is this correct?

3. Apr 17, 2007

### lalbatros

I think you should describe the geometry with more precision. (my feeling)
Do you mean a collimated beam shining with some angle on the thin film?
Or maybe it is a point source of white light illuminating the whole film?
How is the reflexion observed?
I think these links could be useful:
http://en.wikipedia.org/wiki/Anti-reflective_coating
http://en.wikipedia.org/wiki/Fresnel_equations
The derivation of the Fresnel laws in an EM course could be instructive.
Finally, you should ask yourself the question: why would different colors behave differently in the reflexion? What is the reason?
I could not find the full theory of the thin film on the web, you should try.

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