How to Make a Rainbow
Did you know the light around us (usually from the sun, but also from the lights in our house) is made from a mixture of different coloured light? White light as it is called is actually made up of all the colours of the rainbow.
A rainbow is an arc of colours seen in the sky opposite the sun caused by the refraction ( bending of light ) and dispersion ( splitting up ) of sunlight in drops of rain or mist. When the sunlight hits the raindrop it is dispersed into the colours of the rainbow.
The colours of the rainbow are: red, orange, yellow, green , blue, indigo and violet.
Refraction is when light bends as it passes through a transparent material such as glass or a prism.
Did You Know?
A rainbow is actually a full circle of light, but as they are viewed from the ground we only see a semi-circle. Sometimes from an aeroplane you can see full circle rainbows.
How to get the colours of a rainbow with a prism
You can see the colours of the rainbow by refracting sunlight through a prism or bubble. This a great way to prove that white light is actually made up of different coloured light.
Right angled prism
Large sheet of white paper
Dark coloured cardboard
Tape or glue
Large tray or sheet of thick card
Stick your large sheet of white paper either to one side of a large tray or to a big sheet of thick cardboard.
Cut out two equal sized pieces of the dark cardboard, bend over one edge of each about a cm thick and stick to the white card leaving just a small gap between the two pieces so you get just a small stream of light passing between them
Tilt the tray or cardboard so the sunlight flows through the gap between the cardboard. This gives us a very fine beam of white light which makes it easier to see as it comes out the other side of the prism.
Place your prism over the light, you should see the colours of the rainbow.
Why does this happen?
The white light, which enters the prism, is a mixture of different frequencies, which get bent differently thought the prism, this means we see the colours separate after they have passed through the prism.
Make a Rainbow with Bubbles
This is a very easy way to see the different colours that make up light. You can use shop bought bubble mixture or make your own. This is the recipe we use.
250ml of good quality washing up liquid
1 litre of hot water
2 tablespoons glycerine
You can also add a couple of tablespoons of cornflour to make the bubbles extra strong, but this does make them a bit more messy.
Add the washing up liquid to the hot water and stir very gently.
Add the glycerine and stir again.
Leave for a couple of hours before using, the longer you leave the mixture the better it is.
When your mixture is ready, blow some bubbles and look for the colours.
Can you see the rainbow effect on the bubbles?
You see the colours of the rainbow in the bubbles because the bubble film is made up of a few layers, a layer of soap, a layer of water and then another soap layer. When light hits the bubble film it is refracted ( bent ) splitting the white light into separate colours.
Have you ever seen a double rainbow? This is where a second, fainter arc can be seen outside the main rainbow arc, caused by the light reflecting twice inside the water droplets. The colours of the second arc are the opposite way round to the main arc, with violet on the outer edge and red on the inner.
This post was written by Emma of Science Sparks
Emma is a busy Mum to three who is passionate about science education. You can find Emma’s experiments and activities over at Science Sparks which is full of fun, creative and engaging science based activities for children of all ages, perfect for home or school. Find out more at Science Sparks www.science-sparks.com
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