Young's double slit and coherent light

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Discussion Overview

The discussion revolves around the conditions for constructive and destructive interference in Young's double slit experiment, specifically focusing on the role of phase and coherence of light. Participants explore the implications of the textbook's assertion that coherence, rather than strict phase alignment, is sufficient for interference patterns.

Discussion Character

  • Conceptual clarification, Debate/contested

Main Points Raised

  • One participant questions the textbook's claim that coherence is sufficient for interference, suggesting that phase alignment is necessary for constructive interference to occur at path differences of m λ.
  • Another participant proposes that if the incoming light has different phases at the slits, the locations of constructive and destructive interference would also shift.
  • A third participant reaffirms the initial assumption that constructive interference occurs only when the waves are in phase at the slits.
  • A later reply acknowledges the clarification provided by another participant regarding the conditions for interference.

Areas of Agreement / Disagreement

Participants express differing views on whether coherence alone is sufficient for interference, indicating a lack of consensus on the necessity of phase alignment at the slits for constructive interference to occur.

Contextual Notes

The discussion highlights potential ambiguities in the definitions of coherence and phase, as well as the implications of these concepts for the formation of interference patterns.

sorax123
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Hello all,
I was looking through my textbook on the double slit and it talks about constructive interference occurring at path differences of m \lambda and destructive interference occurring at path differences of (m + 1/2) \lambda where m is an integer. This is obvious if the waves leave the 2 slits in phase, however the book states that it is not necessary for the waves to be in phase, just for them to be coherent (ie. constant phase difference). Now I understand how the fringe pattern would form here but I fail to understand how the above conditions can be true as for the two to be in phase, one would have to travel further to be in phase at the arbitrary point P. Is this a textbook oversight or am I missing something?
Thanks,
Dom
 
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If the incoming light has different phases at the slits, the points of constructive/destructive interference will be different as well, right.
 
So the constructive interference only occurs at m \lambda if in phase at the slits as I assumed?
 
I see, thanks very much for clearing that up.
 

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