Colours of a soap film

Colours of a soap film
Figure 3: thin film interference in a soap bubble. Notice the golden yellow colour near the top where the film is thin and a few even thinner black spots

The iridescent colours of soap bubbles are caused by interfering of (internally and externally) reflected light waves and are determined by the thickness of the film. This phenomenon is not the same as the origin of rainbow colours (caused by the refraction of internally reflected light), but rather are the same as the phenomenon causing the colours in an oil slick on a wet road.

As light impinges on the film

  1. some of it reflects off of the outer surface
  2. some of it enters the film and reemerges after reflecting off the second surface
  3. some of it enters the film and reemerges after bouncing back and forth between the two surfaces from 1 to n times

The total reflection observed is determined by the interference of all these reflections. Since each traversal of the film causes a phase shift proportional to the thickness of the film and inversely proportional to the wavelength, the result of the interference depends on these two quantities. So at a given thickness, interference is constructive for some wavelengths and destructive for others, so that white light impinging on the film is reflected with a hue that changes with thickness.

A change in colour can be observed while the bubble is thinning due to evaporation and draining. Thicker walls cancel out red (longer) wavelengths, causing a blue-green reflection. Later, thinner walls will cancel out yellow (leaving blue light), then green (leaving magenta), then blue (leaving a golden yellow). Finally, when the bubble's wall becomes much thinner than the wavelength of visible light, all the waves in the visible region cancel each other out and no reflection is visible at all. When this state is observed, the wall is thinner than about 25 nanometers, and is probably about to pop. This phenomenon is very useful when making or manipulating bubbles as it gives an indication of the bubble's fragility.

Interference effects also depend upon the angle at which the light strikes the film, an effect called iridescence. So, even if the wall of the bubble were of uniform thickness, one would still see variations of colour due to curvature and/or movement. However, the thickness of the wall is continuously changing as gravity pulls the liquid downwards, so bands of colours that move downwards are usually observed.


Wikimedia Foundation. 2010.

Игры ⚽ Нужно решить контрольную?

Look at other dictionaries:

  • soap and detergent — ▪ chemical compound Introduction       substances that, when dissolved in water, possess the ability to remove dirt (detergent) from surfaces such as the human skin, textiles, and other solids. The seemingly simple process of cleaning a soiled… …   Universalium

  • The Candidate (1972 film) — Infobox Film name = The Candidate caption = Theatrical release poster director = Michael Ritchie producer = Walter Coblenz writer = Jeremy Larner starring = Robert Redford, Peter Boyle music = John Rubinstein cinematography = Victor J. Kemper,… …   Wikipedia

  • Spring (television soap) — Spring is a Flemish Belgian television soap made by Studio 100 for children s channel Ketnet. Six seasons have been taped since the summer of 2002; the last ran from December 31, 2007 till March 2008. Season 1 *Spring is a dance school run by the …   Wikipedia

  • performing arts — arts or skills that require public performance, as acting, singing, or dancing. [1945 50] * * * ▪ 2009 Introduction Music Classical.       The last vestiges of the Cold War seemed to thaw for a moment on Feb. 26, 2008, when the unfamiliar strains …   Universalium

  • light — light1 lightful, adj. lightfully, adv. /luyt/, n., adj., lighter, lightest, v., lighted or lit, lighting. n. 1. something that makes things visible or affords illumination: All colors depend on light. 2. Physics …   Universalium

  • Interference (wave propagation) — Two point interference in a ripple tank. In physics, interference is the phenomenon in which two waves superpose each other to form a resultant wave of greater or lower amplitude. Interference usually refers to the interaction of waves that are… …   Wikipedia

  • literature — /lit euhr euh cheuhr, choor , li treuh /, n. 1. writings in which expression and form, in connection with ideas of permanent and universal interest, are characteristic or essential features, as poetry, novels, history, biography, and essays. 2.… …   Universalium

  • List of Teletubbies episodes and videos — This is a list of Teletubbies episodes and videos. # # Title 1 Ned s Good Bike March 31, 1997 The first episode. Teletubbies watch a father and son riding their bicycles, and then a magical flag appears in Teletubbyland.  …   Wikipedia

  • Five (TV channel) — Infobox TV channel name = Five logosize = 200px logofile = Five logo.svg logoalt = Five logo launch = start date|1997|3|30|df=yes picture format = 576i (SDTV 16:9, 4:3) share = 4.6% share as of = June 2008 share source =… …   Wikipedia

  • Coronation Street — Title sequence of Coronation Street (Introduced on 31 May 2010) Genre Soap opera Created by …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”