What is doing the work in the motor effect?

  1. When electrons move through an armature, the magnetic field produced by the current interacts with the magnetic field it's moving through. This interaction causes a repulsion which produces the spinning of the armature in a motor.

    Would someone please explain what is doing the work in producing the force that is exerted on the armature? Magnetic field? Electric field?
  2. jcsd
  3. jedishrfu

    Staff: Mentor

    The electrons traveling thru the wire are attempting to move to a lower energy state and thus are doing the work.
  4. The work is done back at the power plant, pushing the electrons through the circuit.
  5. There must be something more to this. If electrical energy is transfered to mechanical energy as in the motor effect, wouldn't some work have to be done in this process?
  6. jedishrfu

    Staff: Mentor

    Perhaps If you think of it in terms of a stream and a water wheel. What is causing the water wheel to turn? The water, right. Why? Because the water is flowing from a higher potential to a lower potential and pushes the water wheel causing it to rotate. The electrons are doing the same thing only it involved electromagnetic forces.

    If you reversed the process and used the motor as a generator then it would push the electrons back to the battery doing work to raise the electrons potential.
  7. Okay...so from what I read here and other places, I will summarize:

    1. Power plant supplies the work creating the electric potential energy.
    2. Current flows into motor, which is electric kinetic energy.
    3. Electrons flowing through a magnetic field cause a magnetic field interaction which converts the potential energy of the fields into the mechanical energy of the armature. Work is being done here also.

    Sound right to everyone?
  8. Yes, but if you want to get picky, #1 is problematic in that you could go back to the water in a hydroelectric dam that creates the power from gravity. In other words, depending on how precise you want to be, you have to say what ACTUALLY supplies the power IN the power plant.
  9. An ideal motor would be 100% efficient. All the energy going in would be converted to mechanical energy. You can buy brushless motors that are >95% efficient.

    The remaining losses are typically due to the residual winding resistance, eddy currents, bearing friction and air drag on the rotor.
  10. Why does it have to be at the power plant? This type of reasoning will lead you back to the formation of the sun and the universe... IMO this is no way to answer the question. When we say that a rock gains energy as it falls we say that the gravitational field does the work on the rock, because it is that which is supplying the force along the direction. We do not say that the seismic event that raised the rock up there millions of years ago did the work.
  11. sophiecentaur

    sophiecentaur 14,686
    Science Advisor
    Gold Member

    Yes. It just gets to a 'chicken and egg' argument with. possibly, the Big Bang at the start of it all. You are always allowed to have a black box somewhere with "Energy Source" written on it.
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