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Electric and magnetic field connection

  1. Jan 31, 2016 #1
    So the electric and magnetic fields are linked, when they're at 90 degrees and self propagating they're a photon. I sort of know you can have TE and TM propagation.
    But I'm having trouble seeing how the electric field link is maintained with magnetism; can someone explain to me where the electric filed is in a magnet? For instance, say you have either a permanent magnet, or a magnet caused by moving electric charge. Say it was just a rectangle, with magnetic flux inside it, either changing flux or stationary, I don't care. Where is the respective linked electric field?
    Please feel free to sketch any pictures for a simple explanation, I'm not fussy about quality.
    Thanks!
     
  2. jcsd
  3. Jan 31, 2016 #2

    cnh1995

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    I am no expert but this is what I think, based on my very limited knowledge..Electric and magnetic fields are the two componens of a single 'electromagnetic field'. Change in electric field results in magnetic field and change in magnetic field results in electric field, as described in Maxwell's equations. Both the fields are present when both of them are changing with time (e.g.light). Otherwise, only one of them shows up, depending on the source.
     
  4. Jan 31, 2016 #3
    Yeah thanks, I do vaguely remember deriving Maxwells equations, and I agree with your comment. However I wonder how the electric field can be hidden with a permanent magnet. I would like someone to depict according to Maxwells equations where the electric field was in an AC transformer or inductor.

    Thanks anyway
     
  5. Jan 31, 2016 #4

    cnh1995

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    Electric field is developed in the winding, which is responsible for "induced emf" in both primary and secondary of the transformer. Electric field is also developed in the core. It is responsible for the eddy currents in the core material. Transformer core is designed to minimize these eddy currents. It is an important issue in core design.
     
  6. Jan 31, 2016 #5

    davenn

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    as far as I'm aware, there is no electric field associated with a stationary magnetic field from a permanent magnet
     
  7. Jan 31, 2016 #6
    Yeah, I guess rather than some sort of electric field vector, you could consider circular electric paths around the magnetic flux in the core.
    Thanks
     
  8. Jan 31, 2016 #7
    Yeah, I can see how this would be so according to Maxwell's, but it seems weird for me to understand (because I've just started research the standards model of particle physics) with some electromagnetic field throughout space-time.
    Thanks
     
  9. Jan 31, 2016 #8

    davenn

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    why do you think it is weird ?
     
  10. Jan 31, 2016 #9
    Well if there was this field (electromagnetic) throughout the universe, and perturbations in this field, such as the movement or spin of electrons caused electromagnetic waves through it, which were comprised of two phenomena: electric fields and magnetic fields.Then it is counter intuitive to have a magnetic field and not an electric one....although In writing this I just thought of a hypothesis about where the electric field in a permanent magnet is: inside the magnet in the internal electrons, like the electric field is radial to the electrons in the permanent magnet...
     
  11. Jan 31, 2016 #10

    davenn

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    I have been trying to figure out a better way to describe the situation for a permanent magnet vs an electromagnet
    and I hope some one else will chime in if I haven't quite got it right for you

    In say a bar magnet, there is no radiated electric field as the negative electric field of the electrons is cancelled out
    by the positive field of the protons within each atom, so there is a zero net field being produced

    This, however, is different in an electromagnet or just a straight wire that is carrying a flow of current/charge
    A moving charge generates a moving magnetic field and a moving magnetic field results in a moving electric field.
    Both of which are radiated out from the current carrying wire

    There is one place where you can have an electric field but where thee charges are not moving
    can you think of where that would be ?


    cheers
    Dave
     
  12. Jan 31, 2016 #11

    Drakkith

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    Note that an observer moving relative to a bar magnet (or vice versa) would see part of the magnetic field as an electric field instead. Therein lies your link. Relative motion. A purely electric field is seen as being partially electric and partially magnetic by an observer moving relative to the source. A purely magnetic field is seen as partially magnetic and partially electric by an observer moving relative to the source.

    I believe the real idea of linking electric and magnetic fields together into a single EM field is that each can be seen as a manifestation of the other quite easily.
     
  13. Jan 31, 2016 #12
    A capacitor or battery?

    Yeah, ok, so what you're both saying is that there really is only one 'field' the 'electromagnetic' field, and the appearance of either a magnetic field or electric field is due to special relativity, so with a stationary electric or magnetic field (like a bar magnet) you shouldn't expect the other, but if one is moving than you should expect the other to make an appearance.
    Thanks
     
  14. Feb 1, 2016 #13

    davenn

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    yes

    yup indeed :smile:


    Dave
     
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