| Description |
An oil slick looks colored because of a phenomenon called interference. If the reflections of light striking the top and bottom layer of the oil are in phase (the peaks and troughs of the waves coincide) the lightwaves will reinforce each other; if they are out of phase (the peaks of the light from one reflection coincide with the troughs of the other), they will cancel each other. So, if the thickness of an oil film is, for example, 540 nanmeters (the wavelength of green light), then the two reflections of the greenish light will be in phase, as shown in the diagram, and add, and the two reflections of other wavelengths will be out of phase and interfere, so the slick will look greenish. |
