Thin Film Interference Problem: A hair is placed at the edge..... 1. The problem statement, all variables and given/known data Thin Film Interference Problem: A hair is placed at the edge between two 10.0 cm glass plates of n= 1.52. Light of 400 nm wavelength shines on the glass and an interference pattern is formed. If the separation between the second and fourth dark fringe is measured to be 0.800 mm, find the diameter of the hair. 2. Relevant equations I think I'm supposed to use the equation 2*d = m*L_air / n_glass, where L is the wavelength , but I don't know how to solve for m, what to take from the rest of the problem. 3. The attempt at a solution I'm having a hard time visualizing the problem and I don't know how to find m. I thought about maybe m is the length of a glass plate divided by the length of one fringe which is the distance from the second to the fourth fringe divided by 3? Any help is appreciated.