  Electromagnetic Sensor.
Ah, this brings back memories. I made this thing some time in high school: It's supposed to be a general purpose "microphone" for electric or magnetic fields or vibrating metal parts. I turned the handle on a little toy wood lathe, and got a coil of fine wire from a small electric motor. Behind the coil are a couple of permanent magnets from Radio Shack. If you connect it (using the RCA jack at the base of the handle) to an audio amplifier you can actually hear things when you hold it near something that's producing oscillating fields (e.g. a speaker, electric appliance, etc). The idea behind the permanent magnets is to make it work with any vibrating metal, not just electrically-active objects, but that part never really worked as well as I'd hoped.
Source: Theodore Gray
Contributor: Theodore Gray
Acquired: 23 December, 2007
Text Updated: 23 December, 2007
Price: Priceless
Size: 5"
Composition: CuFe+C(H2O)
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