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What is Lenz's Law of Electromotive Forces and How Does It Work?

  1. Dec 6, 2012 #1
    I'm in grade 12 physics trying to understand how motors work. My teacher is useless.

    I read the official law, but I do not understand how it conceptually works.

    Here is the aplet he gave me, if you want to explain with respect to a visual.

    Thank you very much! I really need to understand this. It is the first thing that seems applicable to the real world.
  2. jcsd
  3. Dec 6, 2012 #2


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    What exactly are you confused about? The site explains exactly what happens, so it would help if you could tell us specifically what doesn't seem to make sense.
  4. Dec 6, 2012 #3
    It is difficult to say.

    Why do electrons spinning in the same direction attract?

    When the north pole enters the ring, why do the electrons move?

    Why do they stay still when the magnet is still?

    Why is the current reversed when the north pole is taken away?

    Edit: Actually, why do electrons flowing through a wire even have a magnetic pull?
    And in a wire with current flowing through it, how is the north pole and south pole determined if the magnetic field is a circle?
  5. Dec 6, 2012 #4


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    Because their magnetic fields line up with each north pole facing the south pole of the next one.
    Faraday's law of induction! http://en.wikipedia.org/wiki/Faraday's_law_of_induction

    When the magnetic field changes, electrical charges feel a force that accelerates them in a particular direction.

    When stationary the magnetic field is no longer changing and no force is generated on the charges.
    The direction of force depends on if the field is increasing or decreasing.

    It's just the way it works. A moving charge is seen by another charge as having a magnetic field. As for current through a coil, use the Right Hand Rule: http://en.wikipedia.org/wiki/Right_hand_grip_rule
    If you grip a solenoid (the whole thing, not just around one loop) with your fingers in the direction of current flow, your thumb points towards the magnetic north pole.
  6. Dec 7, 2012 #5
    Okay, I'm begginning to understand.

    But how do the electrons feel the pull or repel of a magnet when the iron is unmagnetized? And how do you determine direction of force (or current flow)

    Finally, I got solenoid, but how does one determine the n and s pole of a straight, single wire? (I.e why does parallel wiring attract and serioes with current flowing opposite repel?

    Thanks a lot. These are the last questions I think because they are the essence of what I need to know. I just didn't know what I was talking about before. A reply is very greatly appreciated! Thanks a lot!
  7. Dec 7, 2012 #6


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    Charged particles always have north and south magnetic poles because they have intrinsic spin. When iron is not magnetized these poles just don't line up and you don't have a macroscopic magnetic field.

    A straight wire does not have a north and south pole. The lines of magnetic force form a circle around it as the pictures on the wiki articles shows. If I were to put a small compass near it and move it around the wire the needle would orient itself with its side towards the wire and would stay that way. The north pole of the needle would align itself in the direction of the arrows.

    Once you make a coil you orient the wire in a way that causes lines of magnetic flux to all point to one side of the coil, creating a north and south pole.

    If you have two parallel wires the magnetic lines will come around each wire and either meet head on and repel in an opposite current setup, or meet and add together in a same current direction setup. It's hard to explain.
    Last edited: Dec 7, 2012
  8. Dec 7, 2012 #7


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  9. Dec 7, 2012 #8
    I appreciate all the help!!
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