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So can you use electromagnetic fields to repel uncharged objects?

  1. Jun 10, 2003 #1
    I can see how you can attract conductive objects with an electric field, but I'm wondering if it's actually possible to use some sort of electromagnetic phenomena to repel objects, like in Star Trek, or something

    Also, how does a Tokamak fusion reactor keep the plasma in place with magnetic fields? Does the plasma have any net charge, or is it uncharged all in all?
     
  2. jcsd
  3. Jun 10, 2003 #2
    The plasma in a Tokamak is a soup of ions without their electrons. So they can be influenced by electrical fields. Acutally, magnetic fields are the main component used to keep the plasma in place. Electrical fields are usually used to heat it up.
     
  4. Jun 10, 2003 #3
    There a gadget which "throws" rings

    of conductive material just by ramping up a magnetic field in a solenoid. But a static electric field just attracts dielectric objects in much the same way that a magnetic field attracts magnetic materials.
     
  5. Jun 10, 2003 #4
    plasma is a nickname for ionized gases. for an object to become ionized it must be hyper charged. therefore, yes plasma does have a magnetic charge and that is how the feilds keep it from touching the outer edges.
     
  6. Jun 10, 2003 #5
    and in answer to your primary question: no, i don't think so. if the object is completly uncharged then definatly no, but you have to remember, at least at the subatomic level, almost everything has a charge. (positive proton, negative electron, ect.) so, who knows?
     
  7. Jun 10, 2003 #6

    chroot

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    Re: Re: So can you use electromagnetic fields to repel uncharged objects?

    You don't 'hyper charge' gases to ionize them -- whatever that means. You heat them up.

    Also, there is no such thing as a 'magnetic charge.'

    - Warren
     
  8. Jun 10, 2003 #7

    chroot

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    The answer to this problem is largely one of polarisation.

    Take any neutral material you'd like. Despite the fact that it is outwardly neutral, it is built from charged bits -- positive nuclei and negative electrons. If you apply an external electric field, the material becomes polarised -- the electrons are pushed one direction, and the nuclei the other. The atoms, which are roughly spheric in the absence of an external field, essentially stretch out when a field is applied.

    Now say you have an electrode near your material. There is a net polarisation due to the external electric field; one side of the material is more positively charged than the other. Say the electrode is positive, and the strong external field oppositely directed, so that it pushes nuclei toward the electrode.

    The result -- you guessed it -- is that the neutral material is indeed repelled by the electrode.

    Keep in mind that for many materials, an external field would have to be enormously strong to be able to polarise the atoms very much.

    - Warren
     
  9. Jun 10, 2003 #8

    drag

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    Greetings !

    Last things first...
    A plasma means separate "free" charged particles.
    The plasma in the Tokamak is not charged however
    being a plasma means that it has free neucleuses and
    electrons that are separate. Now imagine a magnetic
    field that is parallel and on all sides of a cross section
    of the plasma ring in the Tokomak (the ring and
    the field go "into the screen"). If a positive or negative
    charge attempts to move somewhere sideways from the ring
    axis it is emmidiately affected by the magnetic field
    according to the right (right ? ) hand-rule (or
    the left if it's an electron) and thus forced to circle
    around the axis unable to escape.

    Now, if it can gain more transverse energy it can increase
    it's radius (you basicly have a Hall current - a torroid
    shape current along the axis of the ring). Anyway, the
    whole thing is a balance between the EM fields heating
    the plasma, the energy from the occasional fusion reactions
    and primarily the balance of charges and consequently
    energies between the ions and the electrons in the plasma.

    In short, it's very complex stuff so we'd better leave
    it to those crazy plasma physicts...
    Yes, I think. I'm really no expert so I may be making some
    mistakes here, so please correct me if I'm wrong.

    Light pressure happens because each atom is like a tiny
    magnet and it can thus be affected by EM waves.
    Another possibility is to accelerate the nucleuses of
    the atoms in an ordered fashion in a single direction.
    Either way you'll need EM waves at a frequency that
    is below the ionisation freq. of the relevant atoms
    and you'll need lots of them. Also, the first method
    requires huge amounts of energy and is thus hardly practical.
    I believe the second possibility may be promising, but
    I really honestly know practicly nothing about this.

    Live long and prosper.
     
  10. Jun 10, 2003 #9
    Oh, right

    So you just have to put a strong magnetic field in there, and the plasma's positive cores will go one way, and the electrons will go the other way, but it's all good so long as it doesn't touch anything

    I have a job helping a guy who's head of the University of Washington's fusion project, but all I really know is enough to keep away from the equipment, and not to close doors that say not to close them

    I'm just redesigning their database, see, since they have a large binder they keep all the data in right now..

    So the conclusion is that there's no way to repel non-charged materials except with radiation pressure, eh? All right, then
     
  11. Jun 10, 2003 #10
    Re: Re: Re: So can you use electromagnetic fields to repel uncharged objects?


    thank you, i couldn't quite think of how to phrase my responce. but heat/charge whatever, it's pretty hyper.
     
  12. Jun 11, 2003 #11

    HallsofIvy

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    Marcilla: "I have a job helping a guy who's head of the University of Washington's fusion project, but all I really know is enough to keep away from the equipment, and not to close doors that say not to close them."

    Hey, that's what it's important to know!! :smile:
     
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