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Magnetic field lines direction.

  1. Jun 17, 2012 #1
    It might seem trivial for most of you but i am confused by the definition of direction of magnetic lines. It's well known the magnetic field is directed from S to N but if one looks from outside and follows the magnetic line then one come from N to S. I am aware of that magnetic lines are closed but it is still confusing. and when one brings to bar magnets close to each other the same situation happens: inside each magnet S -> N, in between N -> S. Can someone shed some light on this topic?
     
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  3. Jun 17, 2012 #2

    sophiecentaur

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    The only lines you 'see' from a bar magnet are the ones outside it. You can regard them as existing inside as well - just as they do 'inside' a solenoid. When you put two bar magnets end to end, this is the same as when you add coils to a solenoid. The lines 'join up' to form longer ones that go around all the turns.
    It is necessary to remember, here, that these lines of force that we are all so fond of are not necessarily 'really there'. They just represent the path that an isolated North seeking pole would take. They are just a way of looking at things so don't get too hung up on them.
     
  4. Jun 17, 2012 #3
    Thanks for answering! I am aware that such lines are just a way of representing a force field.
    what prompted me is that when i needed to think of how the magnetic field is directed between two bar magnets i should draw lines N -> S whereas by convention the direction is S-> N and this direction is realized within the magnets. here's the rough picture.
     

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  5. Jun 18, 2012 #4

    sophiecentaur

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    Your diagram looks right to me. Are you just trying to justify it against the simple rule that you first learned at School? If you are then don't worry. If magnetic lines of force are continuous then they cannot be expected to go just from A to B, which is what that simple rule suggests. Our knowledge of magnetism has moved on from the original rule that was invented when all they had was lumps of lodestone (permanent magnets).
     
  6. Jun 18, 2012 #5
    Yeah, i think it's not as trivial as it seems. thank you!
     
  7. Jun 18, 2012 #6

    sophiecentaur

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    Our initial education in Science is often, necessarily, over simple and gives most people a problem when they start thinking deeper about it.

    For instance, How come the North Pole of the Earth, attracts N poles of magnets?? Jeez, how could the North Pole be a South Pole??
    It isn't always made clear that the N pole of a bar magnet is, actually, called a North SEEKING pole. Mr Wastsisname never made that clear to me and I spent a long time worrying about that one.
     
  8. Jun 18, 2012 #7
    i was also confused by this geographical-physical mismatch.
     
  9. Jun 19, 2012 #8
    I wonder, do you have the same confusion about electric current flowing from the + to the - around an external circuit, yet flowing from - to + through the emf (internal circuit)? It is a common problem when physical properties/quantities are represented by closed loops shown as lines.
    The N pole of a bar magnet is defined as the ' north seeking pole' if this was not made clear to you in your text book (unlikely) or by your teacher then ask for a refund.
     
  10. Jun 19, 2012 #9

    sophiecentaur

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    HAHA the old devil's bound to be dead by now. He must have been about 100 yrs old in 1959!
     
  11. Jun 19, 2012 #10
    What happened in 1959 to have a great effect on physics of magnets?
    Faraday had it sorted out way back when........1959???
     
  12. Jun 19, 2012 #11

    phyzguy

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    Michael Faraday died in 1867.
     
  13. Jun 19, 2012 #12

    tiny-tim

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    NOOOOO!! :cry:

    faraday and long ago … :smile:
     
  14. Jun 19, 2012 #13

    sophiecentaur

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    Fourth form Physics. Michael who????
     
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