Final answer:
The colorful effects on a soap bubble or oil slick are due to thin-film interference, a phenomenon where light waves reflecting from different surfaces of a thin layer, like a soap bubble, interfere with each other, creating bright colors.
Step-by-step explanation:
The bright colors observed in a soap bubble or an oil slick on water when illuminated by white light are due to thin-film interference. This phenomenon occurs when the light waves reflected from the top and bottom of a thin layer, like a soap bubble, interfere with one another. The colors that appear are a result of constructive interference, where the light waves enhance each other, producing the brightest colors and distinct patterns seen on the film's surface.
When light interacts with objects that have a size commensurate with its wavelength, interference effects become highly noticeable. In the case of a thin film, which has a thickness less than a few times the wavelength of light, various colors become visible due to the interfering light waves. These fascinating and vivid displays are direct evidence of the wave nature of light and the interference that occurs when light waves overlap, either constructively or destructively.