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Any electrical spark creates radio waves and acts as a transmitter. You hear sparks on a radio as interference. That's why lighting makes radios crackle, and even the tiny spark in a switch is enough to make a noise on the radio when turning on a light.
Accompanying Sheet:
http://www.secretlifeofmachines.com/images/radioset.gif
Please see http://www.secretlifeofmachines.com for more information
Thanks to Tim Hunkin the creator for allowing these excellent videos to be freely distributed on-line.