In the experiment for interference using the concept of air wedge, the point where the glass plates touch in an air wedge is a dark fringe.

Question

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When light waves pass through the air wedge, they undergo interference, resulting in a pattern of bright and dark fringes. The point where the glass plates touch is a point of minimum thickness and maximum separation, causing destructive interference and a dark fringe to be formed.

In the Experiment for Interference Using the Concept of Air