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Pumping electrons without magnetics?

  1. Sep 21, 2009 #1
    Is it possible to push electrons down a wire if a wheel applying pressure to the wire were rolled down it? Another way to cause the pressure would be to apply a heat source down the wire.
     
  2. jcsd
  3. Sep 21, 2009 #2
    That's what the Van de Graaff high voltage generator does.
     
  4. Sep 21, 2009 #3

    jambaugh

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    As for using pressure, no not really. As for heat, yes, but...
    The electrons will flow slightly away from the hot point until the extra pressure due to the heat is offset by the electrical potential. You couldn't actually "pump" them along a wire in the sense you seem to imply.

    However using wires of different metals in which the electrons respond to heat to different degrees (different Seeback coefficients) you can effectively make a heat engine. This is a thermocouple. The temperature difference will drive a current and you actually can generate electricity this way

    You can get even more effect with semiconductor materials oppositely doped. This is known as a Peltier junction.

    This is how the Voyager space-craft were powered. They travel too far from the sun to use solar cells. Using a plutonium pellet which generates heat as the plutonium decays and a thermoelectric generator, power is generated to operate the craft.

    What is more this effect can work in reverse. Running a current through a Peltier junction causes heat to be pumped from one side to the other. These are how the little electronic refrigerators you plug into your car's cigarette lighter work. The are also used to cool the processor in some PC's.

    Check out the wikipedia article:http://en.wikipedia.org/wiki/Thermoelectric_effect" [Broken]
     
    Last edited by a moderator: May 4, 2017
  5. Sep 21, 2009 #4

    jambaugh

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    Not quite the same thing. The Van de Graaff generator doesn't mechanically push electrons along a conductor. Rather an insulating belt mechanically carries the electrons up the potential difference between base and top.
     
  6. Sep 21, 2009 #5
    That's true, the belt is an insulator.
     
  7. Sep 22, 2009 #6
    those crystals in lighters give off electrons when they're compressed. It should work with them no?

    If so then all pumps, and turbines should be able to remake into electron pumps.
     
  8. Sep 22, 2009 #7

    jambaugh

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    Those are piezoelectric crystals. They are different from conductors and what is happening is not the same as "squeezing out electrons" in the sense discussed earlier.

    For one thing the main property of a piezoelectric material is that deforming them produces an electrical potential, not a current. This electrical potential can then pull electrons through conductors placed on the surface of the crystal.

    The spark you see from the lighter is not electrons flowing one way but rather electrons being pulled back and forth as the crystal vibrates. The piezo crystal is acting more like a bell than a pump.

    [edit: Let me however add that yes you could put a diode in the circuit with the piezo-crystal and together they would act as an electron pump. The crystal is kind of like a piston and the diode kind of like a valve.]
     
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