My best lesson - Remove shades of grey from colour knowledge

13th February 2015 at 00:00

Starting a lesson on refraction by showing the video for the song Roy G Biv by They Might Be Giants often takes students by surprise. But they soon see my reasoning when they realise the lyrics are all about the colour spectrum. I sometimes sing along, and occasionally the students join in too.

With this and some introductory questions concluded, it's time to get the equipment out. The pupils need a triangular prism, a ray box and a comb. Turn the lights off and black out the windows, then get the class to project a rainbow on to a screen. The students are always impressed by how the white light turns into all the colours of the spectrum.

Next, ask pupils to make a colour wheel by colouring a sectioned circle red, green and blue. Get them to carefully attach the wheel to a 9V motor and ask them what they will see when it spins. They will probably have got the general idea by now, but temper their enthusiasm by explaining that the colours they have chosen are not likely to be pure so the result may not be a pure white (it always comes out grey).

That's all the essential curriculum learning taken care of, so next I like to blow my students' minds. Many children will never have seen a Magic Eye picture - you can even get Gifs now in which a 3D image appears to move. Provide some Magic Eye pictures and watch how the pupils delve into the colour spectrum with real enthusiasm.

Finally, ask the pupils to recreate Isaac Newton's famous experiment where he recombined the spectrum from a prism, using a second prism to make white light once more - proving that the prism did not add the colour.

Gavin Rayner teaches at Saint Nicholas School in Old Harlow, Essex

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