Question

Thin films (soap bubbles and gasoline) often have multi coloured appearances that change while you watch. Explain the colourful appearance of these films and why their appearance changes with time. (In regards to the wave model of light and dispersion)

Answer 1

Soap molecules have one end that repels water, and one that attracts it, and these molecules move to the inner and outer surfaces.

Soap bubbles are colored because of the thickness of the film - or rather, its thinness - determines whether iridescence is apparent. Light is reflected from both the inner and outer surface of the soap bubble .When an incoming ray of light strikes the outer surface of a bubble, part of the light ray is reflected immediately, while the other part is transmitted into the soap film. After reaching the inner surface of the film, this transmitted light ray is reflected back toward the outer surface. When it leaves the bubble, it travels in the same direction as the ray that was immediately reflected and is, therefore, parallel to that ray.
If these two rays of light are reflected back so that their wavelengths are "out of phase" with each other, the second ray will partly cancel out the reflection of the first ray. This is called destructive interference, which results in a reduction of color intensity. If, however, the wavelengths of the two reflected rays are "in phase," they will enhance each other. This is called constructive interference. The light rays that are reflected off the inner surface of the bubble travel further than the light rays that are reflected off the outer surface.
So if white light shines on a bubble, the film reflects light of a specific hue, and this hue changes with the film’s thickness.

Why they change Colour
The colors of a bubble are dependent on the thickness of the film. A bubble becomes thinner and thinner as it dries out (due to evaporation), before finally popping. As the surface film of the bubble becomes increasingly thinner, a change in overall color can be seen. Thick walls cancel out longer wavelengths in the red range. As the bubble film gets thinner, yellow wavelengths are cancelled out. As it gets even thinner, green light is lost. Beyond this point, even shorter wavelengths in the blue wavelength range disappear.

Peace Bro x

Answer 2

Thank you :)