Everyday Life & Technology
Why do soap bubbles show colours?
A soap bubble shimmers with colour. Puschel explores light in its very thin skin.
The short answer
A bubble's thin film reflects light at its outer and inner surfaces. The returning light waves overlap. This makes some colours stronger and others weaker. The colours change with the film's thickness and your viewing angle.
An imagined Wusel scene
Puschel and Flauschi investigate
Puschel wants to copy a bubble's coloured bands. Before he finishes, they look different. Flauschi views the same bubble from the side; its colours change there too. He draws several views and labels them: not painted stripes.
Try explaining it
Why can the colours of the same bubble change?
Choose a), b) or c), then explain your choice.
- a)Film thickness and viewing angle affect the light.
- b)Fixed coloured stripes in the film merely change position.
- c)The entire film is rebuilt from a new coloured substance.
Show the explanation
Correct: a): Film thickness and viewing angle affect the light.
A bubble's thin film reflects light at its outer and inner surfaces. The returning light waves overlap. This makes some colours stronger and others weaker. The colours change with the film's thickness and your viewing angle.
Word help
- interference
- Light waves overlap and can reinforce or weaken one another.
Explore in more detail
Here you will find longer explanations and further details. You can explore them together.
Understand step by step
How it works – simply explained
A thin film forms the shell
A bubble has a very thin liquid skin. Some light reflects at its outside and some after travelling through the film.
Light paths meet
Depending on colour, these contributions can strengthen or weaken each other: interference. Film thickness matters.
Colours may move
Thickness changes and viewing angle matters, so coloured patches vary. No paint is added; light creates the appearance.
Why colours change as a bubble moves
The film has different thicknesses in different places. Light reflected from its two surfaces can reinforce or weaken different colours, meaning different kinds of visible light. Changing thickness or viewing direction changes this interaction. Colours shift without coloured paint inside the bubble. Keep bubble solution away from mouths and eyes.
References for this explanation: [1]
The key points again
Discovery 1
A soap bubble has a very thin skin of water with soap.
Source: [1]
Discovery 2
Light reflects from both sides of this film. Light waves can reinforce or weaken each other.
Source: [1]
Discovery 3
Different colours stand out with different thicknesses and viewing angles. The stripes are not painted onto the bubble.
Source: [1]