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Problem with magnets and poles

  1. Mar 13, 2015 #1
    I have several bar magnets with the north and south poles labeled on them. It is my understanding that a compass itself is a tiny magnet and the north (often the red part of the compass) end is itself a north polarity. This means that this end would point towards a south pole of a magnet. From every reference book or website I've looked at, the north end of the compass should point along the magnetic field and direct itself towards the south pole.

    Every compass that I bring near these brand new bar magnets behave the opposite as expected. The north end of the compass points towards the labeled north pole of each and every magnet. Either all of these magnets are mislabeled or there is something that I'm missing.

    I know for a fact that the problem is not in the compasses...they all correctly point towards our geographic north.

    What's going on here?
     
  2. jcsd
  3. Mar 13, 2015 #2

    Simon Bridge

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    The compass needle has a north-seeking pole. Useful to add the "seeking" part in your head when thinking about these things.

    ... probably the magnets are not labelled the way you expected.
     
  4. Mar 13, 2015 #3

    davenn

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    compasses DO NOT point to the geographic north , they point to the magnetic north pole ( well the south pole end of the compass needle does)
     
  5. Mar 14, 2015 #4

    Simon Bridge

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    Historically, (in a nutshell) the direction towards the pole star (the bit of the horizon below the pole star) was called "north".
    ... the north-seeking end of the compass, and thereby of all magnets, is so named because (by common observation) the direction it points was/is kinda close to the bit the the horizon below the Pole Star.


    A compass acts as a reasonable approximation to the direction of "North" to stand in for the Polaris when it is not visible, that is, often enough to be useful for navigation over short distances. Longer if you correct for the difference. Much of the time. Compasses acting up is also common... i.e. if there is another magnet nearby. Whence the study of magnetism.

    This means that "magnetic north" (as opposed to geographic north) is actually (above) a south-seeking magnetic pole.
    It is easy to get confused.

    Anyway - OP just wanted to say that the compasses used were not at fault. Just replace North-magnetic for geographic North and we have satsfied the technical terms. It is common-enough use that compasses point "north".

    Also see: http://amasci.com/miscon/miscon4.html#north
     
  6. Mar 14, 2015 #5

    CWatters

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    If the planet has a north pole at the North pole which end of the compass would be attracted to it?
     
  7. Mar 14, 2015 #6
    I'm aware that there is actually a magnetic south pole located near our geographic north pole. The problem I'm having is that multiple magnets (new and old ones that I found) do not behave as expected when a compass is near them. The red (north) end of every single compass always points towards the north pole of these bar magnets.
     
  8. Mar 14, 2015 #7

    CWatters

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    Do they behave the same when they are some distance from the compass?
     
  9. Mar 14, 2015 #8
    same reaction when close and farther away from the magnets
     
  10. Mar 14, 2015 #9

    Simon Bridge

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    Have you compared with other magnets ... i.e. not new ones?
    How are you determining the polarity of the magnets - besides using a compass?

    It is difficult to figure out what is the case without seeing the details of how you are testing them.

    However there are not that many possibilities.

    1. the compasses are faulty
    2. something environmental is throwing the compasses off
    3. the magnet poles are not labelled correctly (or the labeling is misread/misunderstood)

    A properly functioning magnetic compass with no external influences will determine the correct polarity of the magnet.
    I'd do the test with the simplest compass possible ... you have not said what kind of compass was used.
    I'd do the test in widely separated places moving nothing but the magnet and the compass.
    And I'd read any documentation that comes with the magnets carefully.
     
  11. Mar 14, 2015 #10

    Dale

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    I am not sure what the issue is. Seems like just a labeling convention to me. The physics don't care what end is labeled what, and different magnet manufacturers may have different labeling conventions. The point is that a given pair of magnets will attract one way and repel the other way.

    I think that Simon Bridges point number 3 is the most likely. As long as a given pair always attracts the same way then the physics is satisfied.
     
  12. Mar 16, 2015 #11

    CWatters

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    Perhaps try converting some of the magnets into compasses by floating them on a bit of cork/wood/foam. See what happens.
     
  13. Mar 16, 2015 #12
    I was thinking the same thing. I'm going to try it today.
     
  14. Mar 16, 2015 #13

    sophiecentaur

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    I remember choosing to ignore my Physics teacher's use of the word "Seeking" and was confused for a long time. I then sussed out that the Earth's 'North Pole' is, in fact a 'South Seeking Pole'.
     
  15. Mar 16, 2015 #14

    Simon Bridge

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    If you don't believe the compass test, then why would you believe this one?
    What is this test going to tell you that you have not already found out by other means?
    Well, you've done it by now so ... what did you find out? :)

    What kind of magnets are these, who made them, and where did you get them from?
    Have you compared with other magnets ... i.e. not new ones?
    How are you determining the polarity of the magnets?

    It is difficult to figure out what is the case without seeing the details of how you are testing them.
    However there are not that many possibilities. etc.
     
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