Very basic electromagnet vs permanent magnet question

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Discussion Overview

The discussion revolves around the comparison between the behavior of an electromagnet and a permanent magnet, particularly in the context of induced currents in a circuit when the electromagnet is activated. Participants explore the implications of Lenz's Law and the direction of induced currents in relation to the movement of magnetic fields.

Discussion Character

  • Debate/contested

Main Points Raised

  • One participant questions whether switching on an electromagnet is equivalent to pushing a permanent magnet to the left or right, expressing confusion over the textbook's explanation.
  • Another participant suggests that comparing the electromagnet's activation to moving a permanent magnet may not be a useful model due to the complexities involved in changing magnetic fields.
  • A different participant asserts that the textbook is incorrect regarding the direction of the induced current, stating that it should circulate in the opposite direction to the current change in the magnet coil.
  • One participant references Lenz's Law as a relevant principle to consider in the discussion.

Areas of Agreement / Disagreement

Participants express disagreement regarding the textbook's explanation, with some asserting that it is incorrect. There is no consensus on the best model to use for understanding the situation.

Contextual Notes

The discussion highlights potential limitations in the textbook's approach and the assumptions made about the comparison between electromagnets and permanent magnets. The complexity of magnetic field interactions and induced currents is acknowledged but remains unresolved.

MironeDagains
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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.

Problem?: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)
 

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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).
 
MironeDagains said:
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.
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.
 
See Lenz's Law.
 

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