Make a rainbow

A rainbow’s arc of colour is caused by sunlight hitting droplets of water. Light reflects off the surface of the raindrop, which causes it to bend. Some light enters the raindrop before reflecting back out.

Sunlight is made up of all the colours we see in the rainbow, although it appears white. When light is bent (refracted), different colours bend by different amounts, so they spread out. That's why we see colours fanning out when in a rainbow.

But even if it’s not a rainy day, you can make your own rainbow!

Materials:

Dishwashing liquid

Water

Small bowl/dish (for mixing bubble mixture)

Sheet of plain white paper

Bubble wand (or turn anything into a bubble wand as long as it has at least one hole to stretch bubble mix over that you can blow through, like a straw, cylindrical tube, strainers, handles of craft scissors – be careful!)

Steps:

1. Make your bubble mix by adding 1 part dishwashing liquid to 10 parts water in a small bowl/dish. It's best to let it rest overnight. If you have trouble making bubbles, add more dishwashing liquid.
2. Place a sheet of white paper in a brightly lit place, such as next to a window or under a bright light (eg a lamp).
3. Dip a bubble wand (or your make-shift bubble wand) into the mixture and blow into the hole. Look at the light shining through the bubbles against the white paper background – do you see any colours? If you can’t, try shining a torch light directly through the bubbles.
4. Bonus experiment: Dip the mouth of a lid or cup straight down into the soap solution. Pull it out slowly – a soap film should have formed over the opening. Turn the lid or cup onto its side and hold it above the piece of paper. Can you see stripes of different colors forming?

So what's happening?

Like leftover raindrops in the air, bubbles also spread out the colours of light.

A soap bubble is a super thin film of soapy water, with air inside.

When light hits the bubble, some of it will bounce off the surface while some will pass through. Some light is then reflected off the internal surface of the soap film. This causes the beam of sunlight to split up into separate light rays travelling in different directions that look very colourful.

Are there other things at home that you’ve noticed can make a rainbow? Perhaps you’ve caught a glimpse of one when sunlight hits different objects at just the right angle…