Making rainbows: Exploring Light with Prisms

Activities & Days Out / 25 January, 2020 / Nanny Anita

Making Rainbows: Exploring Light with a Prism

EC came home the other day with a reading book all about rainbows, after finishing it he decided that he wanted to make a rainbow. We have talked about and made our rainbows before using paint (check out the craft here), but we have never actually made a proper rainbow using light. Luckily a few months ago I bought a prism from Amazon to use with our light box, so this seemed like a wonderful way to use it again.

Make sure you follow my science board on Pinterest for more ideas.  Don’t forget to save the pin for later. 

You will need:

  • Prism*
  • Torch

* if you don’t have (or even if you do have one) a prism you might want to experiment with other glass objects like a bottle.

Not a great shot, but you can see the rainbow in the corner of the picture.

Not a great shot, but you can see the rainbow in the corner of the picture.

To begin with we took our prism and torches into the playroom and tried to make them against the white doors, then we set up YC’s bedroom so that it was completely dark and started playing around to see if they would show up better in the dark.

Using EC's Batman torch. Not a really clear rainbow, but you can see how the colour has changed around the edge of the light.

Using EC’s Batman torch. Not a really clear rainbow, but you can see how the colour has changed around the edge of the light.

Both YC and EC were fascinated with how the light seemed to bounce of into different directions. They both had lots of why questions, and although I could answer some of them (based on my GCSE physics knowledge from a long time ago) I couldn’t completely answer why the light split into 7 different colours, or at least I couldn’t answer it in a satisfactory way to a 6 and 4 year old. EC decided that it was magic that made it do it, and that maybe I should go back to school!


The science behind it:

  • White light can be split into a spectrum.
  • Light is made up of wavelengths, which are refracted as they enter and leave the prism. This basically means that the light is bent. Different wavelengths are refracted at different amounts; the shorter wavelengths (like violet) are refracted the more, whereas the longer wavelengths (like red) are refracted least. This causing the coloured light to spread out.
  • In the case of rainbows, the water droplets act as the prism.

Screen shot 2016-01-14 at 1.37.47 PM

This activity may help development of:

  • Understanding of rainbows and light
  • Scientific enquiry

Pin for later:

Exploring light experiment by using a prism.

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