Interference patterns in thin films

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Discussion Overview

The discussion revolves around the phenomenon of interference patterns in thin films, specifically in the context of a practical application involving the measurement of a fiber's diameter using interference bands observed between glass plates. Participants explore the nature of these interference patterns and the conditions under which they occur.

Discussion Character

  • Homework-related
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions why interference patterns are separated when multiple light beams transmit through the film.
  • Another participant notes that multiple reflections occur between the interfaces and asks for clarification on what is meant by "separated."
  • A third participant requests a clearer explanation of the original question, indicating confusion about the inquiry.
  • A later post presents a specific scenario involving a fiber's diameter measurement using interference bands and asks about the occurrence of destructive interference and its relation to the measurement process.
  • One participant suggests that the inquiry is a homework question and emphasizes the need for the original poster to demonstrate prior effort in solving the problem before seeking assistance.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus on the original question regarding the separation of interference patterns, and there is disagreement about the appropriateness of the question's placement in the forum. The discussion remains unresolved regarding the specifics of the interference patterns and their implications for the fiber measurement.

Contextual Notes

There are limitations in the clarity of the original question, as well as potential dependencies on definitions related to interference and the specific setup described in the homework scenario. The mathematical steps required to relate the observed interference bands to the fiber's diameter are not fully explored.

haha1234
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Why the interference patterns are separated when there are many light beams transmit through the film?
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Thanks!
 
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There are multiple reflections between all of the interfaces. What emerges will be the sum of all these.
What do you mean, in this context, by the word "separated"?
 
Yes, I think you need to explain your question more clearly. I too cannot understand what you are asking.
 
This is the question

An investigator finds a fiber at a crime scene that he wishes to use as evidence against a suspect. He gives the fiber to a technician to test the properties of the fiber. To measure the diameter d of the fiber, the technician places it between two flat glass plates at their ends as in the figure below. When the plates, of length 15.0 cm, are illuminated from above with light of wavelength 610 nm, she observes interference bands separated by 0.555 mm. What is the diameter of the fiber?

I don't know why there are interference patterns separating,and I want to know if destructive interference occurs,how to measure the diameter of the fibre?
 
This is clearly a homework question. It should be in the Homework section at the very top of the index.

You cannot expect a simple answer for this sort of question on PF. You need to demonstrate that you have actually tried for an answer on your own. Say what you have found out so far and what you think about it. We do not spoon feed students. The topics of thin film interference and Newton's Rings will be thrown up in hundreds of hits on Google. Read what Wiki has to say about it and then come back to discuss it.
 

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