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What kind of current creates magnetism?

  1. Jul 20, 2008 #1

    I read in some book that current creates magnetism.
    but what current? DC or AC currents?
    steady or changing currents?
    transformers works with ac currents and not with dc.
    this is confusing me...

  2. jcsd
  3. Jul 20, 2008 #2


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    Science Advisor

    Either kind. A constant current, i.e. direct current, produces a constant magnet field. It was "well known" that static electricity did not affect a magnet and thought that electric and magnetic fields were completely different thing until Hans Christian Oersted, in 1820, happened to place a compass beside a wire with electricity flowing through it. The compass did not point toward or away from the wire but turned parallel to the wire.

    An alternating current will produce a magnetic field that is not constant but alternates itself- which in turn produces an alternating electric field- that is how a transformer works, changing one type of electric field into another.
  4. Jul 20, 2008 #3
    Just wanted to add to the transformer part. If you have two wires next to each other (in parallel) and have a DC through one, there will be a constant magnetic field around that one wire and the other wire will have no current/no field while sitting in the static field of the first wire.

    Pass AC instead of DC and the field constantly reverses, expanding from and collapsing onto the wire each time it cycles. This has the effect of the second wire passing through a magnetic field (the field passing around the wire is relatively equal to the wire moving through the field) which will generate an AC in the second wire whose power (watts) is the same but whose volts and amps may be different depending on the wire ratios.
  5. Jul 20, 2008 #4
    Thanks a lot for the info.
    now I get it.
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