Light Reflection: Path Length Difference?

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Homework Help Overview

The discussion revolves around the path length difference of light reflecting from a thin film. The subject area is optics, specifically focusing on the behavior of light in thin films and the effects of reflection.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants explore different interpretations of the path length difference, considering factors such as film thickness and refractive index. There is a discussion on the implications of reflection from different surfaces and the potential phase change upon reflection.

Discussion Status

Some participants express confidence in their reasoning while others seek clarification on the thought processes involved. Multiple interpretations of the path length difference are being explored, and there is an ongoing evaluation of the assumptions made regarding the problem.

Contextual Notes

Participants are considering the effects of the angle of incidence and the properties of the thin film, including its thickness and refractive index. There is an acknowledgment of the phase change that occurs during reflection from an optically denser medium.

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Homework Statement



When light reflects from a thin film back toward the source, what is the path length difference?


The Attempt at a Solution



A. It is equal to twice the thickness of the film.
B. It is equal to the thickness of the film.
C. It is equal to half the thickness of the film.

I have rules out C. I think the answer is A but I'm not sure.
 
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I'm leaning towards A now. Anyone have any ideas?
 


Tell us why you are leaning towards A and we can help you evaluate that thought process.
 


I guess the path length difference is between the rays reflected from the two surfaces of the film. When light reflects from a "thin" film back toward the source, the angle of incidence is approximately 90 degree. So, the optical path length difference is twice the film thickness times the refractive index of the film. One also has to take into account the fact that a phase change of 180 degree occurs upon reflection from an optically denser medium.
 

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