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Two conceptual questions: Magnetism

  1. Mar 25, 2007 #1
    Questions #1: Will a nail be attracted to either pole of a magnet? Explain what is happening inside the nail when it is placed near the magnet.

    My answer: Yes, the nail will be attracted to either pole of a magnet because the nail is neutral and has no charge whatsoever. When a magnet is placed near a nail, the nail will polarize, meaning that the electrons will move farther or closer depending on what pole of the magnet is closer to it. -- Is this concept of magnetism exactly related to the polarization concept of electricty and charged particles?

    There is one thing I don't get, however. If magnets are similar to electrically charged particles (opposite poles attract and like poles repel), how do magnets attract neutral objects? Neutral objects have no poles but have atoms that have their charges balanced right? Do the magnets attract/repel the electrons? If so, is it because they exert a force on the neutral object because the electrons inside the neutral object are constantly orbiting (i.e. they have a velocity)? I know that in order for the magnetic field to exert a force on a charge, the charge needs to have a velocity. All electrons have a velocity in an atom correct? Why is it that magnets cannot attract non-metal/iron objects? If all objects contain atoms and therfore electrons, why is it that the magnet cannot attract the constantly moving electrons in its atoms?

    Question #2
    How can a current loop be used to determine the presence of a magnetic field in a given region of space?

    My Answer: Well I know a couple of equation that might help me out: F=BIL, B=unI... but I'm not really understanding the concept behind this question. Please help me out here. Thanks in advance! :smile:
  2. jcsd
  3. Mar 25, 2007 #2
    Can anyone please tell me if I'm going in the right direction for #1? Thanks.
  4. Mar 25, 2007 #3
    Magnets can attract nonmagnets if they are iron. Magnets wont just attract any neutrally charged particle. An iron nail may not be a permanent magnet, but it does have magnetic domains. Placing an iron nail in a magnetic field (near a permanent magnet) will allign its domains, and the two will attract. If you rub a magnet over a paper clip, it will be able to pick up other paper clips because its domains are temporarily alligned
  5. Mar 25, 2007 #4
    So magnets don't attract moving electrons in the atoms of objects? What are the domains that you have metioned?
  6. Mar 25, 2007 #5


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    AznBoi, the analogy between electric forces and magnetic forces breaks down because there is no magnetic charge. You're right that the unmagnetised nail will be attracted to the magnet at either pole. This is because the nail becomes temporarily magnetised. In a ferromagnetic material this is because the motions of the electrons line up and create a magnetic field. Generally charges moving in circles make a magnetic field like a bar magnet.

    It's all in Faraday and Maxwell's equations.
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