How to create a rainbow

With a few simple items, you can create a rainbow on your wall at home

1. Set up your bowl

To create your rainbow, the first step is to find a shallow bowl and fill it about half-full. Then place a small mirror into the bowl so that it’s submerged in the water at an angle.

2. Shine a light

Find a light source to shine into the bowl and onto the mirror at an angle. You could use sunlight coming in through a window, or just the LED light on the back of a smartphone.

3. Light bending

When the lightwaves from the light source move from one medium to another medium of a different density (in this case, from air into water), the light bends. This is known as refraction.

4. See the rainbow

When the light bounces off the mirror, it is reflected back out of the water. Hold a piece of paper near the bowl so the rainbow appears on it. If it’s hard to see anything, make the room darker.

5. Spot the colours

Unlike a rainbow outside in the rain, you shouldn’t have trouble seeing all seven colours of the rainbow on the sheet. If you’re struggling, bring the paper closer to see them more vividly.

6. Move the mirror

Try moving the mirror deeper into the water or changing the angle of it. What happens to the rainbow? Try moving the light, too. Does it make the rainbow easier or harder to see?

(Illustrations by Ed Crooks)

Summary. . .

Light from the Sun or from a phone’s LED might look white, but white light is actually made up of different coloured lights of different wavelengths combining into one beam. When it enters a material of a different density –the water –the different wavelengths are split apart slightly, or refracted, to create a rainbow effect.

This article was originally published in How It Works issue 127, written by Stephen Ashby 


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