Sunday 29 July 2012

Science Project: Splitting light

All the colours of light travel at different wavelengths. The length of the wavelengths depends on the amount of energy that the colour has. For example, red light has the longest wavelength, because of this it has the lowest energy. When the wavelengths of the colours change either due to a less or more dense atmosphere, the colours will split.  Splitting white light like this is called Dispersion.

It was Sir Isaac Newton who discovered that white light is made up of a spectrum of colours, that when blended together it produces a white light.  He used a prism to show that white light can be split into a spectrum of colours and then used a second prism to show this spectrum can then be rejoined to produce white light.  It was Newton who named the seven colours of the spectrum, although as we now know, there are more than 7 colours, white light is made of all the colours, even the ones we can't see.

A spectroscope can break the light into the colours that it is made of.  Astronomers use spectroscopes;  They study a star's spectrum to learn about the chemical elements that make it shine.  A spectrum can also show hoe fast a star, nebula or galaxy is moving towards or away from us.

To work out how the stars are moving scientists use the Doppler Shift.   The doppler shift works using the spectrum.  If a light source stays at about the same distance from the earth it's spectrum has characteristic lines like the top diagram in the source below (drawn by Chiara).  If the source is moving away from earth the light waves are longer and the spectrum lines shift towards the red as in the diagram in this middle.  If the object is moving towards the earth the waves are shorter and the lines shift towards the blue like in the bottom diagram.  The reason why this effect is called the doppler shift is after the discoverer, Christian Doppler, an Austrian mathematician and physicist.

Well now on to project splitting light!

What you will need:

  • A piece of cardboard
  • A glass of water
  • A piece of paper and
  • A window

What you will need to do:

1.  Make a slit in the piece of card like this:

2. Fill a glass full of water.

3. Put the card with a slit against the window propped up with the full glass of water placed on the piece of paper like so...

Then when the sun shines through....

I lent the glass forward a little to make it clearer and this was the effect...

How cool is that!


  1. You can make a spectroscope from a box and an old CD which will show you what artificial light is made from - led, florescent and torch all have different mixes. Let me know if you'd like the details I've probably still got them somewhere.

    You can also make white light by mixing the liquid from different colour glow sticks - kinda the reverse of splitting white light. We had a whole session on light and colour at Levington!

    1. I already have a make your own spectroscope covered Helen: I tend to do seperate blog posts for separate projects - even if they are related as I can always link them. I suppose you'll have to see what I come up with next!

  2. Great, just trying to help :)

    1. That's cool :) I'm interested in those glow sticks ~ do you have a link?

  3. No link for the glow sticks I'm afraid, just played around with them. If you google there's probably info out there.
    We cut open three lit glow sticks, one red, one green and one blue then used a pipette to mix small amounts of the colours 'til they became white. Best done in a dark room or box but the results were great :)