Of course Peter Hopkinson was far too kind to use that for the title of his current physics class (officially titled: From Tuning Forks to Rainbows: The Science of Sound, Light, and Colour), but he could have. Who knew physics could be fun? His experiments have the sold-out class giggling and shrieking in delight – and we are even learning a little science! Talk about a spoon full of sugar to help the medicine go down!
Last week’s session on colour was packed with little gems. Remember the colour spectrum that we see when white (sunlight) shines through a prism? Red, orange, yellow, green, blue, indigo and violet. We grew up with the acronym “Roy G. Biv,” but apparently the Brits learned “Richard of York gave blood in vain”. I wonder what the Aussies say? And indigo! It turns out there’s a story there too. When Sir Isaac Newton did his work with the spectrum in the 1660s, it was thought that 7 was a highly significant number: 7 planets (or so they thought at the time), 7 deadly sins, 7 days of the week, etc., so Newton expected to find 7 colours. He didn’t really, so he kind of fudged it with blue and violet, deciding that there was a transitional colour, hence the indigo and voila, 7.
Peter illustrated the science of light through theatre lighting. As kids we all learned that red, blue, and yellow are the primary colours, and it’s their blends that create every other colour. But that isn’t true in the science of light. White light (normal light) actually breaks into red, blue and green. That means that when you put a red filter over a spotlight, you are blocking the blue and green rays, so only the red shines through. Ditto with the blue and green filters. So with paint, we know you mix red and yellow to make orange, but with light you mix red and green to get yellow. Add blue and you’re back to white! Are you still with me, because the coolest part is this next bit? We now know that if you shine your three spotlights (red, blue and green) all on the same spot, the result is a white spotlight, but the performer in that spotlight is going to cast coloured shadows. Three coloured shadows to be precise. A yellow shadow (where the beam from the blue spotlight is interrupted), a magenta shadow (where the green is interrupted), and a cyan (or electric blue, where the red is interrupted). I can’t wait to go to the next concert. I’ll be so busy watching shadows that I’ll probably forget to listen!
(Oh, and the reason for the difference between the science of paint colours and the science of light? Paint and all other opaque objects are reflecting light, whereas rays of light are transmitting light and somehow that makes all the difference.)