1. The problem statement, all variables and given/known data White light (most intense at 550nm wevelength) shines on a layer of water (n=1.33) setting on a sheet of plastic film (n=1.25). What minimum thickness of water will produce destructive interference on the surface? 2. Relevant equations a) phase reversal of light reflecting off an optically denser medium b) n=c/v (?) 3. The attempt at a solution I am absolutely stumped on this problem. 1) The light reflecting off the top of the water layer will be, as I understand it, phase reversed by the reflection. 2) The light will also slow as it enters the water such that v = c / Nwater, and then reflect back through the water to interfere destructively with the light in 1. This seems to tell me that if the water is one molecule thick, there would be destructive interference due to the phase reversal? As you may be able to tell, I'm just flat stumped. Any help greatly appreciated.