Chapter 25.6, Problem 2cTH

A plate of glass $\left(n=1.5\right)$ is placed over a flat plate of plastic $\left(n=1.2\right)$ . A thin film of water $\left(n=1.33\right)$ is trapped between the plates as illustrated in the diagram at right.

Light of frequency $f=4.8\times {10}^{14}Hz$ is incident from above at essentially normal incidence. The locations of the dark and bright fringes, as viewed from above, are indicated in the top view diagram at right.

In this problem, ignore reflections from the top surface of the glass plate and the bottom surface of the plastic.

c. Suppose that the film of water between the plates were replaced with a film of air.

1. Would a bright or dark fringe be seen at the point where the two plates are in contact? Explain your reasoning.
2. Would adjacent bright fringes be closer together, farther apart, or in the same locations as before? Explain your reasoning.