I don't understand how a changing magnetic field or how changing magnetic flux induces an emf. Im trying to find out how a electric geneartor works. Does the magnet pull the electrons toward the south, does the magnetic field produced by the electrons push back the electrons the opposite way it is facing (north or south) when it is moving. So when the coil is facing the north side the magnetic field is pushing it toward the south side and vice versa so. And when the coil goes to the South side it is pushing the electrons toward the North side so it is A/C current. And I've watch countless youtube videos and countless hours on the web trying to find an answer and I can't it doesn't make sense how a changing magnetic field can create an emf and push an electron. enter image description here

  • $\begingroup$ If you have watched so much content, you must have been told about Maxwell–Faraday equation. If you have, why have you rejected it? $\endgroup$ – user154997 Oct 30 '17 at 23:46
  • $\begingroup$ The magnetic field doesn't pull electrons towward or away from the magnetic poles. (An electic charge would work that way). The force for the magnetic field is perpendicular to both the B field and the current direction. Consequently if you turn the wire loop, it creates current, OR if you put current into the loop then it turns. $\endgroup$ – JMLCarter Oct 31 '17 at 0:09
  • $\begingroup$ @LucJ.Bourhis Here the background magnetic field is static, hence no induced electric field. The current arises purely due to the Lorentz forces. It's the opposite case when the contour is still while the magnetic field is changing where you encounter induction. $\endgroup$ – OON Oct 31 '17 at 4:42
  • $\begingroup$ @OON The OP added the sketch after I commented, and it was on his statement "how changing magnetic flux induces an emf". Well, from the point of view of an observer on the wire loop the magnetic flux varies! $\endgroup$ – user154997 Oct 31 '17 at 11:41

I'll give you a hint, and then you should be able to figure it out yourself. Try visualising.

Imagine that I rotate the coil by a small angle. The electrons in the wire attained a velocity during the time I took to rotate it. Using the equation for force on a moving charged particle (here, the electrons in the wire) in an external magnetic field $ [\overrightarrow F = q\overrightarrow v \times\overrightarrow B] $, we know which side the electrons will move (it'll be different for different segments of the wire as the direction of velocity will be different). A potential difference is created due to the accumulation of negative charges on one side, and positive on the other, which induces an EMF. Hence, a current is generated.

{This also explains Lenz's Law which states that in a closed loop, if magnetic flux changes, a current is generated such that the the change in flux is opposed. Basically, if the flux increases, a current is generated such that the flux decreases (direction can be found by the right hand rule).}

Now, since the current is present in an external magnetic field, the individual wires will feel a force $[\overrightarrow F = i\overrightarrow l \times \overrightarrow B]$, and the coil as a whole experiences a torque $[\overrightarrow \tau = \overrightarrow r \times \overrightarrow F]$, which rotates it.

As for why the current is alternating, imagine this whole thing again once the coil is rotated by 180 degrees, and you'll get the answer!


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