Escape the Raindrops

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 Ever wondered how a rainbow forms? Raindrops act like a prism and split the light into the colours of the visible spectrum. The splitting is called dispersion. The splitting is caused by refraction.


Ray diagram showing how sunlight is refracted and reflected in a raindrop



That's not the whole story though. After entering the raindrop, the light is reflected off the back surface. It then travels out of the front of the drop, refracting again at the boundary. If, when this light leaves the raindrop, it happens to travel to your eyes, you see the familiar bow in the sky. What this means is that nobody sees the same rainbow as you. A friend stood next to you sees the light that has been refracted in their direction.


double rainbow, promary rainbow, secondary rainbow, sr machanism



Ever heard of the famous double rainbow? They are formed when the light reflects twice inside the raindrop. Have you ever noticed that the colours in the second rainbow are reversed? The diagram above shows why.


Other affects you may notice when you see a good rainbow are supernumerary bows (green and magenta bows underneath the other bows. These are caused by a process called interference), Alexander's dark band (a dark region between the two bows) and that the area under the bows is very bright.



Do you want a challenge and to find out more about light? Click on the image below….




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