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Very basic electromagnet vs permanent magnet question

  1. Oct 3, 2015 #1
    When you switch on an electromagnet (who's north pole is pointing to the left), is it the same thing as if you had pushed a permanent magnet to the left? Or to the right? I believe it's to the left. But apparently my textbook thinks it's to the right. Who's correct?

    Why I'm asking:

    I've attached an image of the question that is confusing me. It is to my understanding that when you push a permanent magnet through a circuit, the circuit's induced magnetic field will try and oppose the movement of the permanent magnet and so the current within the circuit will go anticlockwise (if you're looking at it from the magnet's point of view as it's pushed through it), that's exactly what my textbook said on an earlier page.


    However, in this question, the electromagnet (to the left of the circuit) is switched on and so is that the same as pushing a permanent magnet to the left? Or to the right? Because if it's to the left, as I believe it is, then the induced magnet created by the circuit should be opposing this electromagnet and the only way it could do that is if the current was going from X to Y.....but the book says that the current is going from Y to X..which makes absolutely no sense because then the induced magnetic field in the circuit will be going the same direction as the electromagnet and that is a big nono!

    Please help me as this has stumped both me and my dad (who did physics in high school and was top of his class...35 years ago)

    Attached Files:

  2. jcsd
  3. Oct 3, 2015 #2


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    Where does your textbook compare switching the electromagnet with moving a magnet?
    I don't think that is a useful model. You change the field strength at some places, but this change happens due to effects you want to neglect in this analysis (field lines not aligned with the long axis).
  4. Oct 3, 2015 #3


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    You are right. Your book is wrong.

    Of course the induced current will have to circulate the counter way around, as to the current change in the magnet coil.
  5. Oct 3, 2015 #4


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    See Lenz's Law.
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