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Direction shown by a compass

  1. Jun 14, 2017 #1
    1. The problem statement, all variables and given/known data
    The plotting compass, initially on the left and pointing to the geographical north, is now placed at point X. Which direction it will show?
    201706141303541000.jpg
    2. Relevant equations


    3. The attempt at a solution
    I think the arrow will point towards the south pole of the bar magnet (to the left). Is this correct?

    Thanks
     
  2. jcsd
  3. Jun 14, 2017 #2

    CWatters

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    What are your thoughts on the soft iron ring?
     
  4. Jun 14, 2017 #3
    I am not sure. Maybe the magnetic field produced by the magnet will "follow" or "carried by" the soft iron ring so the magnetic field will circle around the magnet but in the end the direction will still be from north pole to south pole. The compass is affected by magnetic field so it will point to the south pole.

    So I guess I am wrong?
     
  5. Jun 14, 2017 #4

    CWatters

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  6. Jun 14, 2017 #5
    Oh, so the field will be "contained" by the soft irong ring, leaving a very few or maybe no field at all outside it and the compass will point to the north (same as its initial direction).

    But why can soft iron ring contain the field?
     
  7. Jun 15, 2017 #6

    CWatters

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    Iron is a good conductor of magnetic fields, in effect the iron ring "shorts out" the field.

    Consider a magnet in free space. Lines of flux run from one pole to the other via the space around the magnet. If you put a piece of iron near the magnet the flux finds it easier to flow in the iron so it takes a "short cut" along the iron rather than the original path.

    I suppose it's similar to why there is no electric field in a conductor.
     
  8. Jun 15, 2017 #7
    Thank you very much
     
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