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B Magnetic field around a wire

  1. Mar 18, 2017 #1
    Hi all, the question is in regards to magnetic fields in a wire. Please refer to illustration below to understand my question.
    (https://www.imageupload.co.uk/image/B9f1)

    As you can see in Picture 3 two wires parallel to each other will attract each other if the current is going in the same direction. How does attraction occur? Why don't the wires repel each other since the wire acts like a magnet with the same dipoles parallel to other. For example. t's like 2 magnetic dipoles north and south parallel to each other.

    If we apply this same scenario but the wire is a magnet on a horizontal plane it makes sense but as you can see in picture 1 this is not correct. In picture 1 if the wire was a magnet on a horizontal plane why doesn't it show the results of picture 2?

    Thank you in advance and sorry if it's a silly question. I'm really struggling figuring it out and I know there are smart people on this forum.
     
  2. jcsd
  3. Mar 18, 2017 #2
    Welcome, @Jack98 to Physics Forums!

    Your curiosity for getting the answer to this question is genuine and I appreciate your concern.

    We, in here, try to answer such questions and support the various concepts regarding a specific subject.
    And you are fortunate enough to know that, we have already attempted to answer to this question.
    I am giving you the link of one of the thread of PF(PhysicsForums) discussing the answer to the same question.
    Here it is,

    https://www.physicsforums.com/threads/why-do-parallel-currents-attract.39472/

    I would suggest, to read all the thread replies for understanding this concept in detail.
    :thumbup:
     
  4. Mar 18, 2017 #3
    Wires carrying current have no recognised N or S poles, the force lines go around the wires.
     
  5. Mar 18, 2017 #4
    Yeah, I think the source of the confusion here is that you treat "north" and "south" as actual entities, whereas they are just convenient simplifications of the (usual) bar-type magnet.

    There is no start or end to a magnetic field, all field lines are closed loop. So, what really matters when it comes to attraction/repulsion is whether the field lines of the two magnetic fields meet head-on (repulsion) or are in the same direction (attraction).
     
  6. Mar 20, 2017 #5
    Thank you very much for the link you provided. I hope I find answers to my question.
     
  7. Mar 20, 2017 #6
    Why do compasses show a wire has magnetised dipoles? I'm really confused. I understand magnetic fields are a concept.
     
  8. Mar 20, 2017 #7
    That makes good sense and it's help me further understand magnetism but don't we represent the rotation of the fields as north or south? For example the north field lines are attracted to the south pole in a closed loop. Electric charge fields can be both monopole and dipoles but magnetic fields can only be dipoles does current going through a single wire have dipoles or is it a mono pole? Solenoids is a magnetic dipole and it's easier for me to visualise and understand then a single wire, which I can't wrap my head around.
     
  9. Mar 20, 2017 #8
    I find the use of the term "dipole" entirely misleading when it comes to magnetism.

    As you yourself found out, "North" and "South" don't make much sense when it comes to wires. That's because those terms are kinda shoddy, and only serve as a convenience for when a massive body generates a magnetic field. Where the magnetic fields exit the body people call it "North", where it reenters it's called "South". But of course the magnetic field continues inside the body. So, what's special about those two ends? Nothing really. You could see shave off a centimeter at the ends of a bar magnet, and have new North and South ends.

    All that matters are the circular field lines. And the direction of them is defined through their "handedness", either right handed or left handed.
     
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