North and south pole in an electromagnet

  1. Not sure if this should be in engineering or physics section. Sorry if I got it wrong.

    How do I determine the north and south pole in an electromagnet? Do electromagnets have a constant N or S pole?

    I am making a locking device where a neo magnet will hold a lid down tightly by sticking itself to a piece of steel placed inside the enclosure. I want to make that piece of steel an electromagnet so that when it turns on it will repel the neo magnet enough so I can open the lid. But to do that I need to be able to determine the poles on the electromagnet and keep it constant every time I run a current through the coil.

    If I wrap the coil around the middle of the piece of steel will the opposite ends of the steel be the N or S poles?

    Thanks in advance guys. If you guys have any suggestions for my project I would love to hear it. =)
     
  2. jcsd
  3. right hand grab rule:

    If you grab the electromagnet in your hand with the current in the coils flowing in the direction of your fingers, then if you stick your thumb out, it points in the direction of the magnet's north pole. Current is assumed to travel from the positive end of the battery to the negative.
     
  4. current flows from the negative to the positive in a battery. the electrons are pushed away from the negative and attracted to the positive.
     
  5. oops :blush:
     
  6. Dadface

    Dadface 2,069
    Gold Member

    But the hand rules, left hand rule etc use the conventional( +to -) current direction.
     
    Last edited: May 19, 2009
  7. I think it's positive to negative...http://en.wikipedia.org/wiki/Electric_current#Current_flow I think positive means there is an abundance of electrons so they move to a negative? Not sure...

    Anyways, do you guys think my idea will work? If I turn the electromagnet on, will the poles stay at the same spot every time?
     
  8. with direct current, yes the poles should stay in the same place.
     
  9. I agree with dadface and that is why I wrote "Current is assumed to travel from the positive end of the battery to the negative." (for hand rules) :)
     
  10. k im sure you guys are right about the hand rules and everything , but how can electrons flow from positive to negative , maybe i am missing something.
     
  11. Dadface

    Dadface 2,069
    Gold Member

    You are not missing something the true direction is from -to +.The hand rules use the incorrect conventional direction which goes the other way.I think these rules were devised long before the true current direction was known and for some reason they have remained in the texts.
     
  12. ok thanks for clarifying
     
  13. Hi
    some one please help/ i am ready to throw a screaming fit........

    I HAVE HOME MADE ELECTRO MAGS...THEY ARE GOOD ONES.........POWERED BY A 12 VOLT CAR BATTERY (DC),......WHY IS IT THAT ONE END OF THE ELECTRO MAGNETS...EITHER NORTH OR SOUTH WILL ATTRACT BOTH ENDS (NORTH OR SOUTH ) OF MY NEODYMIUM MAGNETS ...TRIED EVERYTHING....EVEN SOBBING INTO MY PILLOW . WHAT I NEED IS FOR ONE END OF THE ELECTRO, EITHER NORTH OR SOUTH TO REPEL ONE END OF THE NEO AND ATTRACT THE OTHER END OF THE NEO...BEGGING FOR HELP....JIM
     
    Last edited: Oct 15, 2011
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