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EMF canceling in toroidal coil setup

  1. Jan 14, 2007 #1
    Hello All,

    My question concerns induced emf in an air-core toroid setup. This is simply a thought experiment and I think I know the answer to this but thought I would run it past you all anyway.

    Picture a non-magnetic toroidal core with two one-layer coils wound on it 180 degrees apart from each other. Then imagine another coil is wound on top of the first to but this coil goes 360 degrees around the toroid. Now, if an AC signal is applied to one of the two coils on the first layer, I would expect that the arrangement would simply behave like a simple toroidal transformer. But, if both of the windings on the first layer are tied together in parallel and driven with the AC source, is it true that their emf’s would cancel and there wouldn’t be any effect on the secondary coil (coil on the top second layer)? See my drawing for the diagram of this setup.

    Jason O

    Attached Files:

  2. jcsd
  3. Jan 15, 2007 #2


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    Staff: Mentor

    If you drive the two inner coils out of phase, then yes, they would cancel out the net EMF in the outer 360-degree coil.
  4. Jan 15, 2007 #3
    Toroids don't talk to each other very well, especially with a core. But an air wound toroid is basically a cylindrically wound coil bent in a circle, and the magnetic lines should escape it.

    The coupling between these toroids will be very poor.
  5. Jan 16, 2007 #4
    Thanks for the clarification :-).
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