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Transformer generator question

  1. Apr 13, 2015 #1
    Say I have a soft iron piece which somehow has a changing flux in it (for simplicity take 50hz) for the question doesn't matter how the flux got there.
    Now I have a coil and I now take the iron piece and move it back and forth through the coil 50 times a second to be the same rate as my flux.

    Will the current in the coil be as strong as the flux in the core + the energy I added moving it back and forth through the coil or just the flux strength?
  2. jcsd
  3. Apr 13, 2015 #2


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    They will sum together vectorially. In order for a current to be induced the wire needs to cut the flux lines. In a transformer this is accomplished by the flux moving and the wire being stationary. So, if your coil moves in such a way so that it is always moving with the flux no current will be induced in the coil. Have a look at how induction motors work. It is closely related to what you are questioning here.
  4. Apr 13, 2015 #3
    Right, if the induction motor's rotor and it's field spins slower than the field in the stator moves then it has torque (motor mode) , if it spins faster than the stator field then it produces torque on stator (generator mode) but if the rotor and stator fields align as would be when the speeds align then there is no torque on the rotor , correct?

    After you pointed out I saw my flaw , I can't push the very object through which the flux is originating in symmetry with the flux itself and get induction , I could push it in opposite direction while flux goes one way the core can be made to go the other way.

    Well maybe I can then combine induction with lorentz drag to double the current? I'm not sure this is correct but here is the question.
    To make the describtion simple , I will use a simple model.
    A faraday disc , but cut in pieces like a pizza each piece has a small gap to the next one, the ends at the center and outer rim are connected together in parallel.
    A magnet , not a round one but a flat bar rotates around this disc , for this question assume that the side facing the disc has a single pole , now this rotating magnet has a changing field of say 50hz , would I then get those 50hz induced ac current out the connection points of my disc +the input rotational torque supplied to the rotating magnet due to the lorentz drag its field exerted on the conductor?

    This is assuming the magnets field is at the right angle to the conductor , as would normally be in a faraday disc , only the classical situation has the disc spinning and the field static to get lorentz drag.
  5. Apr 13, 2015 #4


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    A faraday disk works in some strange ways. As I understand it, the brush at the outside is where it is at so to speak. You can rotate the magnet with the disk and as long as the brush is stationary you will get a current. I have only read about this. Never tried it.
  6. Apr 14, 2015 #5
    as much as I know is that if you spin a static magnetic field and keep the disc stationary -nothing happens.
    if you spin the disc itself no matter whether the static field source spins or not -current is generated, but as long as the brushes keep spinning at different speed or are stationary with respect to the disc.

    the thing that I don't know is what happens when you have the disc stationary and instead of brushes just connect it to a load and then rotate a changing magnetic field but in such a way that at every instant only alike poles face the disc so that you wont get opposite currents that cancel out.
    The thing I wonder is whether that would only produce induction as with every other chaging b field or would that also create the same lorentz drag that happens in oridnary faraday discs.
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