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Homework Help: The Motor Effect

  1. Jan 27, 2015 #1
    1. The problem statement, all variables and given/known data
    This is not a homework problem but more of a clash of terminology I have encountered for an explanation of why a motor rotates. In class, I have been taught about the Lorentz force causing the armature to turn. Where electrons in the wire experience a force when they experience a magnetic field at right angles to their motion. The directions of the force can be found using Fleming's left hand rule. However, I come across several explanations that do not mention the Lorentz force law or Fleming's left hand rule at all. They explain it in terms of the current fed through the rotor causes the coils in the rotor to turn into electromagnets. These electromagnets have north/south poles which try to chase the north/south poles of the magnetic stator. The video below explains this very clearly (particularly 50 seconds to 2 minutes 20). Which is the more fundamental explanation? These seem like two completely different explanations and surely only one is correct?

    2. Relevant equations

    3. The attempt at a solution
    I'm note sure but I think they may be two ways of looking at the same thing.
  2. jcsd
  3. Jan 27, 2015 #2


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    2017 Award

    Staff: Mentor

    Both are valid. I guess you can call the one with Lorentz force "more fundamental" if you like, but it gets more complicated to use if your coils have some core (or even permanent magnets).
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