AG22: We Trip The Light Fandango

Download Episode 22

This week we talk about light - there's more to it than you think.

So what does the heat that seems to try to cook you when you get in a hot car, the radio that you play as you drive and the X rays that your dentist uses to find that cavity all have in common with a beautiful sunset? The answer is that the glow from your car, the radio signals, the X rays and the light from the sunset are all electromagnetic radiation, one of the fundamental forces in the world. They are all just different flavors of the same thing. You can think of the different kinds of EM radiation as different notes on a piano keyboard. The radio waves are the really deep, low notes down on the left end of the piano keyboard. The heat coming off your car are slightly higher notes and the visible light, the stuff that we can see with our eyes are higher still. Up the the really high end, the sharpest notes of all are the X rays. The different pitches - technically frequency - not only change the way that we perceive the radiation, but also affects how much energy the radiation carries. This is why you don't need to fearful of standing in the glare of a light bulb or next to a radio transmitter but should be very careful around the much higher frequency X rays.

Electromagnetic radiation is all around us - fortunately mostly the safer, lower frequency stuff. In fact, everything that is at all warm, (where warm here means anything above the coldest that you could be, which is -273 C ) naturally radiates electromagnetic radiation. That hot car is radiating EM that we perceive as heat. Turn up the temperature a bit, say on an electric stove and you get 'red hot' - the EM radiation coming off the stove is high enough frequency we see it as a dull red glow. Red light is the lowest frequency light that we can see. The other colors are all of slightly different frequencies with yellow somewhere in the middle and violet having the shortest. We call the EM radiation whose frequency is slightly less than red 'infra-red' and the stuff above violet, 'ultra-violet'.

Since electromagnetic radiation is a sort of wave - think of it as like ripples on the surface of water - you can make it interfere with itself. Interference is something that waves do. Throw a stone into a still pond and you will make a set of ripples, little circular mini-waves. Throw two stones in and you will get two sets of ripples. When those two sets of ripples run into each other something very interesting happens: In places they reinforce each other while in other places they cancel each other out. So when two waves hit each other you tend to get an interference pattern, the waves are alternatively stronger (as the two waves reinforce each other) and weaker - as the waves cancel each other out. You can see that kind of interference by looking at the back of a CD or a DVD. The rainbow that you see coming off the back of a DVD is produced by the light that is reflected off of the tiny dots on the back of the DVD. All those dots reflect a bit of light which then goes out and interferes with the other bits coming off of other dots and we get the rainbow. In the same way, scientists bounce X rays off of the atoms inside of crystals - which causes X rays interference patterns - to try and figure out how those atoms are arranged.

Electromagnetic radiation: The world would be a darker place without it!

The opening theme music for this weeks episode is called Walk With Me by our good friend Jason Dale.

The closing music is Air On A G String, performed by the Gardner Chamber Orchestra with soloist Paula Robison

Russ & Chris