A very thin sheet of glass (n = 1.5) floats on the surface of water (n = 1.33). When illuminated with white light at normal incidence, the reflected light consists predominately of wavelengths 400 nm and 560 nm.
What is the thickness of the glass?
What wavelengths would be visible if a thin layer of water of the same thickness were spread out on top of a thick piece of glass?