optical phenomenon?

Question

What optical phenomenon causes soap bubbles and oil slicks to show colorful displays?

Answer 1

It's called interference, and when you see the colors in a soap bubble or in an oil slick, you are directly seeing evidence of the wave nature of light.

The wavelength of light visible to the human eye varies from about 400 nanometers for violet light up to 700 nanometers for deep red light, with the wavelength order long to short being red, orange, yellow, green, blue, violet. These names refer to bands of color, of course; the colors red to violet blend continuously from one to the next as the wavelength decreases continuously from 700 nanometers to 400 nanometers. You see these colors when you see a rainbow, although the colors of a rainbow are produced not by interference but by dispersion.

White light is a mixture of all of the colors of the rainbow. You can 'synthesize' white light by mixing about equal amounts of the right colors. This is how your computer screen makes millions of different colors even though it has only three different color elements at each pixel in the screen (usually red, green and blue).

You can also separate white light into its constituent colors, in two different ways: by dispersion and by interference. In soap bubbles and oil slicks, the white light is separated into colors by interference.

Both soap bubbles and oil slicks consist of thin films of transparent liquid, of water and oil respectively. Despite the fact that these liquids are transparent, at each surface of the thin films, a small fraction of the incident (white) light is reflected back toward your eye. This fraction is about 4% at each surface. Depending on the thickness of the film of water or oil, and the wavelength of the light being reflected, the waves from the two surfaces either superpose positively, trough on trough and peak on peak, or superpose negatively, trough on peak and peak on trough. Waves from the two surfaces that superpose positively add to form stronger waves, and waves from the two surfaces that superpose negatively subtract to form weaker waves, or cancel out completely. So waves from only some colors reflect back strongly toward your eye; the rest pass on through. As the thickness of the film changes, the colors also change, producing the moving iridescence we find so fascinating and beautiful.

A good book with lots of beautiful pictures is:
"Soap Bubbles, Their Colors and the Forces That Mould Them" by C.V. Boys

An interesting thing to do is to find some low-pressure sodium vapor street lights (the kind that produce the garish, pure deep yellow light) and blow soap bubbles under this light and see what the interference bands look like. These sodium yellow lights contain only one narrow wavelength of light, at wavelength 589 nanometers, so you will only be able to see one set of the interference bands, instead of all the colors. Bluish-white mercury vapor street lights also have light made up of relatively narrow color bands.

Answer 2

The film of a soap bubble is very tiny, ...down to the few angstrom level. So is the wavelength of light. When you see a color being reflected from a bubble, that point in its surface just happens to correspond to the wavelength of that particular color of light. Since the bubble is slightly irregular and the difference in wavelength between red and pink light is quite small, there appears of be a rainbow of colors coming from the bubble. Its thicker parts show reds and thinner parts show blues... hope this helps.

Answer 3

The soap solution have less surface tension. The remain in soap bubbles in multilayers. When sun light passes through these layers, it gets dispersed in to rainbow colours due to interference of lights from different refracting layers. The same occurs in the case of oil slicks also.

Answer 4

Interference of Thin Films: Newton's Rings

The colorful appearance of a soap bubble, the beautiful appearance of a thin film of oil on the surface of water and the colorful feathers of a peacock are all examples of color resulting from the interference of light in a thin film.

Answer 5

it is the phenomenon of interference of light erflected from the top and bottom surface of oil film which results in coloured pattern.

Answer 6

Interference of light rays from a broad source of light, due to reflections on thin parallel films of substances.

Answer 7

hmmm... harmonic interference? it has to do with the thickness of the film and the wavelength of light... but I'm not sure what it is called.