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Coil is moving around ring magnet made of two arch shaped magnets with poles opposing each other like so:

Would a current flow in coil? or be canceled out?

enter image description here

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  • $\begingroup$ The coil is drawn as an open circuit... for a current to flow the circuit must be closed. Can you clarify what is moving, and in what direction? $\endgroup$
    – Floris
    Commented May 6, 2017 at 5:29

3 Answers 3

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By Faraday's law, changing magnetic flux induces an electric field, which in turn leads to an induced current in a closed circuit. In this case, assuming that the coil is part of some closed circuit, yes, current will be induced in the coil. Current will be induced when there is a change in magnetic flux. Observe that when the entire coil is moving through the "same coloured magnet", meaning, when it is moving through a constant magnetic field, no current is induced. However current is induced when it moves through the gaps between the magnets or when it moves from one polarity to the other.

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  • $\begingroup$ thx, I was thinking what type of current would it be ac or dc?, yes coil is shorted of course. $\endgroup$
    – szufla
    Commented May 6, 2017 at 13:30
  • $\begingroup$ It is definitely AC. $\endgroup$
    – Tejas P
    Commented May 6, 2017 at 13:41
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Yes, it will be ac voltage and current. You see that as magnet plate rotates, the coil will be moving in to the lines of flux in the air gap. As it starts to cut true the lines, the voltage will increase to a maximum and decrease as is leaves the gap. it will do this twice per turn. Say the magnets turn at 30 times per minute, the coil will generate two sine waves per turn (60 waves per minute) so we can say the voltage frequency is 1 Hz.

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With the coil in open circuit, you will have a voltage difference at its terminals. Let's assume the coil moves cw or that the magnet moves ccw. Seen from front, let's call the bottom blue N pole and the top blue end S pole. The lines of flux are all concentrated in the iron except at the gaps where they extend in the air to jump from one magnet end to the other. Some of those flux lines will be "swiped" by the coil winding. Using $V=lv \times B$ and looking at the sketch it can be seen that Term 2 will be the positive end of the coil and if a load is placed, current would leave the coil form terminal 2 (conventional current flow). Hope my drawing help clarify the idea.

relative motion, coil and magnets

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