1. The problem statement, all variables and given/known data A transparent oil with an index of refraction of 1.25 spills on the surface of the water (n=1.33), producing a maximum of reflection with incident orange light ([tex]\lambda[/tex] = 602nm in air.) Determine the lowest possible thickness (in nm) of the oil slick. 2. Relevant equations n1[tex]\lambda[/tex]1 = n2[tex]\lambda[/tex]2 3. The attempt at a solution Okay, I know how to get the answer... but I don't quite understand it. The question is asking the lowest possible thickness, and it's producing a maximum of reflection, right? What I thought was, since there's two reflections - one off the oil slick and then another reflection off the water, that would mean 2 phase shifts; creating constructive interference. In that case, wouldn't the lowest possible thickness be 1/4[tex]\lambda[/tex]? I get the answer if I apply the thickness of the film to be 1/2[tex]\lambda[/tex], but I'm not sure why. Also, these may be other questions but they're still related to thin films, if that's okay: how do you know when it's trasmitted light or reflected light? It would have to say in the question, right? And all the questions I've done seem to always have constructive or destructive interference that makes the film of either 1/2[tex]\lambda[/tex] or 1/4[tex]\lambda[/tex] thickness... When is it 0 or something like 3/4[tex]\lambda[/tex]? I'm guessing that's when there's more reflections, perhaps? Thanks for help.