Three experiments involving a thin film (in air) sandwiched between two layers of air are shown with nair < nfilm. If t denotes the film thickness and λ denotes the wavelength of the light in the film, which experiments will produce constrictive interference as seen by the observer? The incident light is nearly normal to the surface.
2nt = (m+0.5)λ
The Attempt at a Solution
I think the solution is I and III will produce constructive interference. I'm not totally sure why, but I think in experiment 1 and experiment 3 light undergoes one phase reversal and t satisfys (2nt = m+0.5)λ. Experiment 2 has 2 phase reversals?