As I understood the tangential force F on a current-carrying conductor in a magnetic field makes the armature of a electric motor move. But actually the groove where the conductor is located in is (almost) field-free.

The field of the current-carrying conductor, however, influences the magnetic field in the tooth flanks (is that right?) which leads to an unbalance of the field forces so that the effective tangential forces in electrical machines mainly arise by Maxwell's tensile stresses on the tooth flanks (it's a machine translation).

I'm confused about this.

  1. Is this explanation correct?
  2. Is there a more simple explanation how it works?
  3. Is this valid for all electric motors?
  4. Any good online source about this?
  • \$\begingroup\$ The article is describing a specific type of motor. Variable reluctance perhaps? \$\endgroup\$ – Brian Drummond Jul 5 '14 at 11:33
  • \$\begingroup\$ @briandrummond the problem is I cannot keep apart the different principles. I don't think its about a reluctance motor which consists of a highly-permeable material and no further magnets or coils, but about all machines which use the Lorentz force mainly. \$\endgroup\$ – user39717 Jul 5 '14 at 11:52

I assume you've read the Wikipedia and How Stuff Works articles about motors, but these just talk about magnetic attraction and repulsion without explaining the underlying physics.

The Wikipedia article on magnetic fields provides a better basic discussion about the relationships between magnetic field, the energy associated with it and the forces that can be generated.

The key concept is that motors produce torque because the tangential force on the rotor is attempting to reduce the total energy of the magnetic fields within the motor.


There are many types of motors. We can basically categorize them into AC and DC.

When current passes through the conductor, in a varying magnetic field, according to Faraday's law of Electromagnetic induction (http://en.wikipedia.org/wiki/Electromagnetic_induction) , there is an electromotive force across the conductor. This torque is what makes the conductor move. This torque is dependent on the armature current, and the field.

T = F*d

F= b*i*l

where T= Torque F= Force d=distance b= Force i= current l=length of the conductor

So, if the torque exceeds the minimum sufficient value, only then the armature moves, giving the motoring action.


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