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Lorentz force system, what to expect?

  1. Feb 15, 2015 #1
    I'm building a system that is using the Lorentz force principle, of when a wire is placed in a magnetic field(##B##) with length(##L##) and has current flowing(##I##) there is a force = ##IL \times B## that would move the wire. I want to take into account of every single thing that will happen after.

    • Inductance in the beginning for current stabilization.
    • Induced-EMF, because there is change in flux due to the motion of the conductor in the magnetic field , ##\epsilon= -vBL## .
    But, prior to motion there is something confusing me, when the wire has current flowing, it produces it's own magnetic field that is parallel to the exterior field and is in opposition, there will be induced EMF that is similar to motional EMF to oppose that change, however, is there a slight attractive/repulsive force between the wire and the exterior magnetic field source(magnet/electromagnet)? Similar to when two wires carrying current are placed near one another (depending on the direction of current) there is a force of attraction/repulsion.

    How can a wire move in a magnetic field due to the Lorentz force, when it's own magnetic field interacting with the exterior field causes an opposing attractive/repulsive force? Although, the wire's magnetic field is parallel to the exterior one, but doubt that makes a difference. Bit confusing on that note.
  2. jcsd
  3. Feb 15, 2015 #2


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    Well, for a motor for example, the wire is being mechanically driven by some means.


  4. Feb 15, 2015 #3
    I should have stated this earlier, but the circuit is DC. Also, so there is a force acting on the wire that is the Lorentz force, at the same time there is a repulsive/attractive force between the wire's magnetic field and the exterior's field?
  5. Feb 15, 2015 #4

    Come to think of it... can the Lorentz force, be considered as a repulsive force...? The force that I was worried about is itself the Lorentz force and a magnetic force(maybe a repulsive force)?

    To be exact of my question, aside from the Lorentz force the wire experiences are there any other magnetic force it experiences that could affect it's motion?
    The only things that I can think of will always be Lorentz force, and the induced-EMF on the wire that is produced from this set-up, no other forces/effects come into mind.
  6. Feb 15, 2015 #5


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  7. Feb 16, 2015 #6

    jim hardy

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    I think you're on the right track.

    In machinery the force is exerted on the conductors as shown in the diagram you posted.
    That other equations can be derived is our good fortune, and is demonstrated by Baluncore's excellent selection of links.
    We don't have to derive from QVcrossB every time.
    But you should drill yourself on those derivations until you believe in them because it is better to intuitively understand a formula than to just memorize it.
  8. Feb 16, 2015 #7
    @Baluncone thanks for those links, great refresher to the concepts.

    I got myself confused, I assumed that the magnetic field produced by the wire and the external fields would interact in a way similar as to how magnets/electromagnets would attract or repel one another, which seems not true. I can conclude that the only force acting on the wire is the Lorentz force. I assumed there might be another force that would resist this. However, the only form of "resistance" that would oppose this change(the wire's motion) is the induced EMF ##\epsilon = -vBL##.

    I have one thing to note here, when the wire creates it's own magnetic field it opposes the external field, would that decrease the external field causing a change in flux therefore having to deal with another induced-##\epsilon##, aside from the induced ##\epsilon## caused by motion? They way I think of it, is if the wire is stationary in that field there is no induced ##\epsilon## (ignoring inductance for a bit).
  9. Feb 16, 2015 #8
    @jim hardy Hey there Jim! Glade to see you participating in this!
    I already believe in those derivations not only mathematically but experimentally too!
  10. Feb 16, 2015 #9
    I want to correct myself and make a few things clear here, I know that the wire would have it's own magnetic field induced due to the flow of current, however, when that current-carrying wire is placed inside the magnetic field, is there any interaction between the two fields that would lead to induced-##\epsilon##? I know that when the wire moves there is(Motional EMF formula), but about the wire's magnetic field and the external magnetic field interacting causing a change in flux somehow? Is there something to account for there?

    I feel as if I'm over complicating things.
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