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Name: Rakshit
Status: student
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Question:
Why the central fringe appears to be light rather than dark in formations of Newton's Rings?


Replies:
Dark only happens if waves cancel. Waves only cancel if they have different phases such as 0 and 180 degrees, or 0, 120, and 240 degrees, or a similar balanced set. Newton's rings are diffraction around a circular object. It is circularly symmetric at the center-point, so all paths to that point will have equal distance and phase. All will be 0 degrees relative to each other. So they must add constructively instead of canceling. Hence a bright spot.

Jim Swenson


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