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Resistors are magnets? — Parallax Forums

Resistors are magnets?

Jorge PJorge P Posts: 385
in General Discussion
I was playing around with some neodymium magnets and got one stuck to a resistor, I noticed that the ends of resistors are south poles at the leads, but north pole in the center. Why? I tested this on several resistors both 1/4 and 1/8 watt that were never near magnets before. Are all resistors like this?

Comments

  • evanhevanh Posts: 15,192
    It'll be the end caps have a ferrous element in them, presumably nickel. Not what I would have thought was a great idea though.
  • lardomlardom Posts: 1,659
    edited 2018-03-25 22:26
    You're right! I just tested a normal magnet on a resister resistor on my desk: There was no effect on the leads but the resister resistor itself stuck to the magnet.
  • ercoerco Posts: 20,254
    edited 2018-03-25 17:19
    The leads are tinned copper, not much to stick to there. And either end of a magnet attracts the center portion, no polarity difference. Don't get lost in the woods and expect a resistor to guide you home. :)

    I still love the trick where you point a screwdriver (or any steel rod) north and bash it with a hammer to magnetize it. Talk about beating some sense into an inanimate object.
  • localrogerlocalroger Posts: 3,451
    A quick search reveals that "non-magnetic resistors" are a thing, suggesting that most normal resistors probably include magnetic materials.
  • Heater.Heater. Posts: 21,230
    Might be worth thinking about when building ones next compass circuit.
  • jmgjmg Posts: 15,148
    Jorge P wrote: »
    Resistors are magnets?... Are all resistors like this?

    Not so much magnets, as magnetic. In effect, you are testing for iron content.

    Copper is soft, and expensive, so it is common to find other materials used where that makes sense.

    You can also find the leads of some resistors have some iron content, especially power resistors.

  • Jorge PJorge P Posts: 385
    I played around with this a bit more, either pole of a magnet is repelled by the center of a resistor... At first I only checked the north pole, but the south is also repelled at the center. I am using a 2mmx2mm cylindrical neodymium magnet.

    Maybe this is for a pick and place machine to pickup and drop a resistor?
  • Dave HeinDave Hein Posts: 6,347
    It doesn't makes sense that the center of the resistor would repel a magnet. Maybe the magnet is just being attracted to the nearest end of the resistor. Is the resistor actually pushing the magnet away, or are you seeing the magnet move toward one of the ends of the resistor?
  • Jorge PJorge P Posts: 385
    Dave Hein wrote: »
    It doesn't makes sense that the center of the resistor would repel a magnet. Maybe the magnet is just being attracted to the nearest end of the resistor. Is the resistor actually pushing the magnet away, or are you seeing the magnet move toward one of the ends of the resistor?

    It sure feels like it is, give it a try!

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