Question

A thin wedge filled with air is produced when two flat glass plates are placed on top of one another and a slip of paper is inserted between them at one edge. Interference fringes are observed when monochromatic light falling vertically on the plates are seen in reflection. Is the first fringe near the edge where the plates are in contact a bright fringe or a dark fringe? Explain.

Answer 1

The first fringe near the edge where the plates are in contact is a dark fringe due to destructive interference.

Step-by-step explanation:

In the setup described, the first fringe near the edge where the glass plates are in contact is a dark fringe. When monochromatic light falls vertically on the plates, interference fringes are observed in reflection. In this case, the path length of the light traveling through the wedge of air between the plates is equal to an odd multiple of half the wavelength of the light. This causes destructive interference, resulting in a dark fringe.