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Magnetic field hypothetical

  1. Jun 14, 2009 #1
    When a wire has current running through it, a magnetic field is created around it, right? And I've seen lots of diagrams of the magnetic field lines wrapped around a wire in a coil-like fashion.

    So, hypothetically, imagine if there was a current running through a wire, and that wire was suspended in a room that was free of any gravity.
    Would metal shavings orbit around that wire in the same direction as the magnetic field lines?
  2. jcsd
  3. Jun 14, 2009 #2
    I think Iron filings would actually follow the magnetic flux rather than the current.
  4. Jun 14, 2009 #3


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    No, that's how you'd expect a magnetic monopole to behave, if one actually existed. An iron filing (for example) would take on an induced dipole, which would simply align with the field rather than "flying" around the flux loops.
  5. Jun 14, 2009 #4
    If the current was held constant they would line up with the magnetic field lines, which would be closed circular loops around the wire. If the effect is to be noticeable this requires that the metal filings have some asymmetry. It's exactly the same effect produced when placing a permanent magnet in the vicinity of metal filings. Since every single filing gets magnetized they would attract each other, and therefore gather in lumps symmetrically placed around the wire. These could be very numerous resulting in a seemingly continuous circle. I think this might result in discrete rings forming, whose separation could be small. The net effect would be that you see contours of the field lines in the space not occupied by metal filings. It all depends on how the filings are spatially distributed before the magnetic field is applied.

    If the current is changing I'm not entirely sure as of what exactly would happen. They wouldn't reflect the changing field at every instant of time, because the changing field induces a current in the filings, which in turns give rise to new magnetic field affecting the filings around it, and I can't tell the net effect. If the field is big enough it might overcome this induction effect and just move in accordance with the field changes.

    Is there a simplifying principle I'm missing?
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