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Help with electromagnets wiring method

  1. May 2, 2012 #1
    I am curious to know, why on a electromagnet that the wire coming in is on the opposite side to the wire leaving?

    Is it due to the way the current comes in and leaves, as in the anticlockwise field in the north so incoming and the outgoing is clockwise south.

    When I say a electromagnet I mean a bar and horseshoe.
     
  2. jcsd
  3. May 2, 2012 #2
    Where the wire joins and leaves the coil is arbitrary, as long as as you have one continual coil (no cut anywhere breaking the circuit) and each coil loop turns the same way around the core. The current that adds the most to the magnetic field is the current through each loop in the coil, not the current through the wires that connect the coil to the battery.
     
  4. May 2, 2012 #3

    Drakkith

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    Staff: Mentor

    Are you referring to actual wires in the coils of electromagnets, or the lines in pictures of magnets that go from one end and loop to the other? I'm only asking because you said "When I say a electromagnet I mean a bar and horseshoe."
     
  5. May 2, 2012 #4
    Here in attachment is a drawing of a basic horseshoe electromagnet showing a single coil of N turns carrying I amps, and the equation for calculating the magnetic field B Tesla in the air gap.
     

    Attached Files:

  6. May 3, 2012 #5
    The actual wires, I know it is a strange question, but I was reading one of my physics books and it pointed out how the wires were wired different on both sides of the magnet; but never gave an explanation as of why. The picture in the book was a horse shoe/ U magnet. The only thing I could see why was that the magnetic field coming in was opposite on either side so making one side north the other south.
     
  7. May 3, 2012 #6

    K^2

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    Doesn't matter. So long as the wire keeps going around the core in consistent direction, be it consistently clockwise or consistently counter-clockwise, where the coil starts and ends doesn't matter. Each loop will have the same contribution regardless of pitch.
     
  8. May 3, 2012 #7
    This is what i've found, without formal education, just tickering around. The direction of the coil wind has no bearing on pole designation. But the direction of current flow does set up opposite poles on either side of the coil. Switching the source current, meaning physicaly switching "+" to "-" and or vise versa, you will then be able to determine pole designation with a permanet magnet and see if the magnet sticks or is repelled away/flipped over. I have used this method many times, with consistant results. You will still need to know which side of your permanet magnet is N and S.
     
  9. May 3, 2012 #8
    This is what i've found, without formal education, just tickering around. The direction of the coil wind has no bearing on pole designation. But the direction of current flow does set up opposite poles on either side of the coil. Switching the source current, meaning physicaly switching "+" to "-" and or vise versa, you will then be able to determine pole designation with a permanet magnet and see if the magnet sticks or is repelled away/flipped over. I have used this method many times, with great sucsess. You will still need to know which side of you permanet magnet is N and S.
     
  10. May 3, 2012 #9
    Thanks for the feed back, well appreciated for clearing that up for me.

    Another question on the same topic. When you look at a 3 pole magnet for example one in a speaker and there is a south pole in the middle and two north either side when the coil is wrapped around that, they are in opposite direction to each other, in my book it say: this is because when current flows in one direction it make one side stronger than the other. How dose this work?

    Is it the same when you put two conductors together and the current flows the same way in both, the repel each other, well something along them line, just a guess.
     
  11. May 3, 2012 #10
    Oh just to say thanks, to everyone else who came back to me well appreciated.
     
  12. May 4, 2012 #11
    Can you show us the coil configuration that you refer to ? Is it one winding that loops into three, what I call ring coils. much like a figure 8 with another loop attached? Without seeing it it's hard to say. How is it that you determined the pole orientation? And are their permanent magnets being used for the core to each coil?

    I would have to disagree with, as you mentioned "this is because when current flows in one direction it make one side stronger than the other." That doesn't sound right to me. Like I mentioned previous I have no formal education in this. I'm just speculating from what I've picked up along the way...

    cheers
     
    Last edited: May 4, 2012
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