Effect on visibility of thin films due to interference

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Homework Help Overview

The discussion revolves around the effects of thin film interference on visibility, particularly in the context of light reflection and refraction through films of varying thicknesses. Participants are exploring how these factors influence whether an observer can see the films and the conditions under which constructive or destructive interference occurs.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants are attempting to clarify the role of reflection versus refraction in visibility, questioning whether light must be reflected to "see" the film. Some are exploring the implications of different interference conditions based on film thickness and phase changes upon reflection.

Discussion Status

There is a range of confusion among participants regarding the problem's wording and the underlying physics concepts. Some have offered insights into the nature of interference and phase shifts, while others express frustration with the clarity of the problem. Multiple interpretations of the conditions are being explored, and some participants are seeking further clarification on specific points.

Contextual Notes

Participants note potential issues with the problem's presentation, including typos and unclear terminology, which may hinder understanding. There is also a discussion about the assumptions made regarding light reaching certain points and the implications of phase differences in interference patterns.

  • #31
brochesspro said:
Sorry, I didn't get you.
Suppose on hitting the film from the left only 5% is reflected. The other 95% reaches the far side of the film, where 75% is reflected. (Is this possible? I don't know.) So then 75% of that is reflected from the LHS, the other 25% emerging. The reflected portion returns to the RHS, 75% of that being reflected and 25% emerging as the third ray directed leftwards.
We have, in the first three rays going leftwards from the film:
5% in the first
95%*75%*25%=15.7% in the second
95%*75%*75%*75%25%=9% in the third
 
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  • #32
haruspex said:
Suppose on hitting the film from the left only 5% is reflected. The other 95% reaches the far side of the film, where 75% is reflected. (Is this possible? I don't know.) So then 75% of that is reflected from the LHS, the other 25% emerging. The reflected portion returns to the RHS, 75% of that being reflected and 25% emerging as the third ray directed leftwards.
We have, in the first three rays going leftwards from the film:
5% in the first
95%*75%*25%=15.7% in the second
95%*75%*75%*75%25%=9% in the third
So this supports my assumption, right?
 
  • #33
brochesspro said:
So this supports my assumption, right?
That was an explanation of how the third ray to the left could be more significant than the first one, so an analysis that only considers the first two is incomplete.
 
  • #34
haruspex said:
That was an explanation of how the third ray to the left could be more significant than the first one, so an analysis that only considers the first two is incomplete.
So in short, no, right?
If so, I think I will stop thinking about this problem.
 
  • #35
brochesspro said:
So in short, no, right?
If so, I think I will stop thinking about this problem.
Good.
 
  • #36
haruspex said:
Good.
Thank you for all your help. The others too.
 

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