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Research question 2: How do the colours on a soap bubble form?
To answer this question we will find the answer to the following sub-questions:
- What colours appear on a film of soap?
- What is light?
- What happens to light when it goes through a soap film?
What colours appear on a film of soap?
Watch the movie below and answer the following questions:
1. Compare the colours you see in the soap film with the colours of a rainbow. Are they the same? If so, do they also have the same order?
2. What colour does the soap film have right before it bursts?
What is light?
Light is just like sound made up of waves.
Sound waves
Small wavelength = high sound
Large wavelength = low sound
Small amplitude= soft sound
Large amplitude= loud sound
Light waves
Small wavelength= light with colour on the 'blue' side of the spectrum
Large wavelength= light with colour on the 'red' side of the spectrum
White light is a mixture of waves with all wavelengths.
Small amplitude= dim colour
Large amplitude= bright colour
What happens to light when it goes through a soap film?
Study the text and use the applet at the bottom of this page to answer the questions below:
3. How does the colour 'magenta' appear on the soap bubble?
Use the words 'wave and interference' in your answer.
4. How does the colour 'orange' appear on the soap bubble?
Use the words 'wave and interference' in your answer.
5. Explain the colour of the soap film right before it bursts.
To understand how the colours of a soap film can form, you must first realize that a soap film has a front and a back surface no matter how thin it is. Think of a piece of paper. It has a front surface and a back surface. No matter how thin the paper is, it will still have a front and a back surface (see image below)
Paper is not transparent so it will reflect most of the light that strikes it. A thin soap film will allow most of the light to pass through (it is transparent). But some of the light will be reflected on the surface of the soap. Just like you can see yourself in reflected in the glass of a window.
The light will reflect on the front and the back surface of the soap film (see image below).
When two waves meet they will join to form a new wave. We call this interference.
- If the two waves are in phase the amplitudes will of the two waves will be added together (left picture). With light waves this will results in brighter light.
- If the two waves are out of phase the amplitudes of the two waves will cancel each other out (right picture). With light waves this will result in complete darkness.
Click on the picture to start the applet. Use the RGB bulbs mode to explain the answer on question 3,4 & 5.
At the bottom of the page you can find a video that gives you a more detailed view of the interference of light waves in soap films.
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