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How does the wire know the magnetic flux has changed?

  1. May 17, 2008 #1
    If we have a metal wire and a magnetic field "inside" it, when the flux of the magnetic field changes, then the wire "reacts" by "creating" an induced current.

    After learning this law, it eventually came to my mind the question: how does the wire know that the magnetic field flux has changed? I mean, in order to note the change, the wire somehow needs to have memory: "the magnetic field flux was x one second ago, and now it's x+dx... ok, it's time to induce a current".

    Inanimate objects, such as wires, i.m.o. only know what happens around them instantly, so i find very hard to understand the fact that an inanimate object can detect a change of a physical variables in two different moments.
  2. jcsd
  3. May 17, 2008 #2

    Doc Al

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    Staff: Mentor

    Good thinking. There must be something going on at the wire to "tell" it to induce a current. And there is. The changing magnetic field induces a surrounding electric field--it's that electric field which drives the current.
  4. May 17, 2008 #3
    Ok, that makes much more sense. The change in the magnetic flux induces an electrical field, so the wire does not need to pay any attention to anything but to the existence (or not) of an electric field. This way the "memory problem" is solved: once there is an electric field (and the wire does not mind about its origin at all), the wire says: "hey, what's up? an electric field is present: ok electrons, it's time to woark: moving on...".

    Thanks for your answer: it has been very clear and precise.
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