# Colors from soap bubble films

1. Jan 8, 2014

### smart_worker

on a soap bubble colours can be seen.my text book says its due to the interference betwewn light waves from the top and the bottom surfaces of thin films.but how?so confused

i tried googling for answer but still i cant find it

2. Jan 8, 2014

### maajdl

This is mainly due to the so called "thin film interference".
See wiki: http://en.wikipedia.org/wiki/Thin-film_interference
See specially these pictures:
constructive interference: http://en.wikipedia.org/wiki/File:Thin_film_interference_phase_1.svg
destructive interference: http://en.wikipedia.org/wiki/File:Thin_film_interference_phase_2.svg

This phenomenon is one of the proofs that light behaves as a wave.

On top of that, if you observe very well the bubble, you will realize that its thickness is not uniform,
and that it changes with time.
At some places the colors disappear completely as if there was a hole: the thickness is very small but still sufficient for the mechanical resistance of the bubble.
The soap also tends to accumulate at the bottom of the bubble and the top becomes thinner.

Related to that is a wonderful lecture by Feynmann that you can find there:

http://vega.org.uk/video/programme/46

In this lecture he relates the wave-like behaviour of light to the interferences, the propagation along a straight line, reflection at equal angles, and refraction. This is to say how fundamental this is. It can even be linked to quantum mechanics and to classical mechanics and why particles moves as they move!

3. Jan 8, 2014

### sophiecentaur

One interesting feature of the colours of oil films is that they are not 'Rainbow colours' they are the result of destructive interference 'knocking holes' in the spectrum of incident white light. The nulls are narrower than the peaks with the simple interference filter so a lot of light is reflected and the colours are bright and nothing like what you can get with pigments - hence they are more fascinating and unusual looking. Insects and bird colouring is achieved this way - hence the vivid and attractive colours. Ain't evolution wonderful?
Multiple layers of different thicknesses can achieve a range of filter responses (Shiny sunglasses and dichroic filters on Halogen lamps).