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Question about north and south poles of a magnet.

  1. Nov 17, 2015 #1
    I've always been taught: North poles attract south poles. Yesterday after studying electromagnetism, I've a question to ask. Here's a diagram:
    4tXhD.png
    In circuits like these, this is how the north and south poles of these electromagnets are defined. Now my question is, is the reason that the South pole of the first electromagnet(Its backside) attracted to the front of the electromagnet in the back because the two circuits have current flowing in the same direction? Is this why in general the north pole attracts the south pole? How does this work in a permanent magnet such as a bar magnet?
     
  2. jcsd
  3. Nov 17, 2015 #2

    davenn

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    Hi there
    Welcome to PF :smile:

    in a straight wire carrying current, there are no north and south magnetic poles as the magnetic field is circular ( a loop) around the wire


    cheers
    Dave
     
  4. Nov 17, 2015 #3
    I'm sorry, but I don't see how this answer is relevant to my question at all. My question is about two closed loops which produce a magnetic field as such:
    curloo.gif
     
  5. Nov 17, 2015 #4

    davenn

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    now if you wind the wire into a coil, then you can create magnetic N and S poles ....

    magnetic-field-in-a-straight-coil-of-wire.gif
     
  6. Nov 17, 2015 #5

    davenn

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    because you first drawings were showing straight sections of wire, so my answer was completely relevant


    D
     
  7. Nov 18, 2015 #6

    CWatters

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    No. It's to do with the energy of the system. Systems tend to prefer lower energy states. This holds for all sorts of systems including those involving gravity and chemistry.

    http://physics.stackexchange.com/questions/64146/the-preference-for-low-energy-states
     
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