Two microscope slides are stuck together and touching on one side where n=1.2 and wedged open on the other where n=1.5. These slides sit in air. When you shine monochromatic light with a wavelength of 500nm on it, you see 8 dark fringes (it is dark on the ends of the slides).
a. Find the distance d between the slides on the side where it's wedged open.
b. How many fringes are there for the same slide configuration when it sits in water rather than air?