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B Metals touching, produce EM waves

  1. Aug 25, 2016 #1
    Can you help me on this question I had for years?

    Every time I touch two metals together (holding them with my fingers) and place a shortwave SSB radio nearby, I hear clicks and noises on the radio.
    Why is that happenning?

    Has anyone observed this phenomenon before?
     
  2. jcsd
  3. Aug 25, 2016 #2

    sophiecentaur

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    Those sparks get in everywhere!
    It strikes me that your two bits of metal (dissimilar?) are forming a simple electrolytic cell (battery) via the acid in the sweat of your hand. It the "bits of metal" are, in fact, wires then you would have the basis of an antenna, which would couple this energy into your receiver. If you are just describing the effect with two small metal items then it's a bit harder to understand how the dimensions can account for what you are hearing.
    Give us a bit more detail, please.
     
  4. Aug 25, 2016 #3

    sophiecentaur

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    There is another possibility, which I thought of whilst driving in the car this morning. If your wires are long, then they could be acting as receiving antennae and having an emf induced between them (or even some current from the mains). This can produce a spark when they are close enough, which will contain power at frequency that your receiver is tuned to.
     
  5. Aug 25, 2016 #4
  6. Aug 27, 2016 #5

    davenn

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  7. Aug 27, 2016 #6

    sophiecentaur

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    The Seebek effect is the 'opposite' to the Peltier effect. Seebek produces an emf due to temperature difference whilst Peltier produces a heat transfer due to an applied voltage. But I don't think the few mV per junction that Seebek can produce could produce enough emf for a spark. Plenty of current available to work a gas cutoff / flame detector solenoid, though, once you have a good contact.
     
  8. Aug 29, 2016 #7

    CWatters

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    Metal on metal noise was once a big problem for people like me that flew radio controller model aircraft. If vibration from the engine caused two bits of metal to rub together it could drive the radio control system nuts causing planes to crash. These days radio control systems have much improved and I suspect are virtually immune.

    Edit: For info radios I used were typically 27MHz AM then 35MHz FM(PCM) and now they are 2.4GHz Spread Spectrum.
     
    Last edited: Aug 30, 2016
  9. Aug 31, 2016 #8
    Well, the basic reason is that a current flows between the pieces of metal. The act of making contact creates tiny sparks that emit radio waves.
    The current can come from several sources: Galvanic potentials, induced potentials from outside sources, including static electricity (as already mentioned).

    You can test this by connecting the pieces of metal with a wire. Now you can make them touch all you want and no noise will be generated (except in very special cases)
     
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