Rainbows and colour
Where do the colours of a rainbow come from?
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Explain
White light has all the colours.
Rain splits it into a rainbow.
White light is really a mix of many colours. A glass prism splits it up into a spectrum.
Each colour bends by a slightly different amount. Violet bends the most, and red the least.
Raindrops do the same to sunlight, and that makes a rainbow.
Each colour of light has its own wavelength, from about 700 nm for red to about 400 nm for violet. 1 nm is a billionth of a metre.
Different wavelengths travel at slightly different speeds in glass, so they refract by different amounts. This is called dispersion.
A red apple looks red because it absorbs most colours and reflects red.
- White light is many colours
- Glass bends each differently
- A rainbow appears
Want the full story?
Sunlight is a smooth spread of colours, and the seven names are only a tradition. Raindrops also reflect light inside, so you must have the Sun behind you to see a rainbow. Screens mix red, green and blue light to make other colours.
Try it at home
You need a clear plastic cup of water, white paper, a sunny window.
You need: a clear plastic cup of water, white paper, a sunny window.
Look for rainbows in a water spray.
- Put the cup of water on a sunny windowsill. Never look straight at the Sun.
- Put white paper on the floor below.
- Move the paper around to find the colours.
What's happening: the water bends each colour by a different amount, and spreads them out.
Physics is life
Your body
Your eyes sense colours.
Daily life
Screens are made of tiny colours.
Nature
Leaves look green.
Space
Starlight shows what stars are made of.
Quick check
Question 1 of 3
Words to know
Spectrum: All the colours of light, spread out in order.
- Spectrum
- All the colours of light, spread out in order.
- Refraction
- Light bending as it goes from one material into another.
- Wavelength
- The distance from one wave crest to the next.