How rubbing a needle on a magnet affects its polarity

  • #1
UserOfPhysics

Homework Statement


It is known that when rubbing a needle on a magnet, the needle will become magnetized.

If you rub the needle on the north side of the magnet, will it point differently than if you rubbed it on the south side of the magnet? Does it matter what direction you rub the needle?

Homework Equations


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The Attempt at a Solution


I actually tried doing that manually. The 1st time I tried, I came to the conclusion that side doesn't matter, it's the direction of rubbing that matters. However, I just did it again and I've come to the conclusion that side matters and direction of rubbing doesn't matter.

Thank you for any ideas. Also, I'm new to the forum, so sorry if I broke any rules :(
 

Answers and Replies

  • #2
Charles Link
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It would seem the best way to magnetize a needle using a cylindrical magnet would be to draw it along the edge of one of the pole faces, pulling it towards you. This is where the magnetic field is the strongest and pointing along the direction of your needle. If you do this on the north pole, the part of the needle away from your hand should acquire a "north pole". Alternatively, doing this on the south pole should give the part of the needle away from your hand a south pole. If you instead draw the needle flat across one of the pole faces, the magnetic field points at right angles to the needle and won't be very effective in magnetizing it.
 
  • #3
UserOfPhysics
It would seem the best way to magnetize a needle using a cylindrical magnet would be to draw it along the edge of one of the pole faces, pulling it towards you. This is where the magnetic field is the strongest and pointing along the direction of your needle. If you do this on the north pole, the part of the needle away from your hand should acquire a "north pole". Alternatively, doing this on the south pole should give the part of the needle away from your hand a south pole. If you instead draw the needle flat across one of the pole faces, the magnetic field points at right angles to the needle and won't be very effective in magnetizing it.
I see, I have been rubbing it flat, but my magnet is square, not cylindrical.

You mentioned that rubbing towards me on the north pole would result in the part of the needle away from my hand to be attracted to north. Would pushing the needle away from me change its attraction, or would it not make any difference?
 
  • #4
Charles Link
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I see, I have been rubbing it flat, but my magnet is square, not cylindrical.

You mentioned that rubbing towards me on the north pole would result in the part of the needle away from my hand to be attracted to north. Would pushing the needle away from me change its attraction, or would it not make any difference?
I believe pushing the needle away from you would be less effective. Pulling it towards you makes it experience an increase in the magnetic field along the needle as it is drawn across the edge by the pole.
 
  • #5
UserOfPhysics
I believe pushing the needle away from you would be less effective. Pulling it towards you makes it experience an increase in the magnetic field along the needle as it is drawn across the edge by the pole.
But it wouldn't change the polarity of the needle, right?
 
  • #6
Charles Link
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But it wouldn't change the polarity of the needle, right?
That's correct.
 
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