1. A thin film of oil (no = 1.50) with varying thickness floats on water (nw = 1.33). When it is illuminated from above by white light, the reflected colors are as shown in the figure. In air, the wavelength of yellow light is 580 nm. a. Why are there no reflected colors at point A? b. What is the oil's thickness t at point B? 3. a. Because it is a destructive interference? the reflected ray from air to oil (phase change) and oil to water (no phase change) so they cancel out? b. Why is this one a constructive interference? I've read that because there is light it is always constructive but when its dark it is destructive is that true?