Electrical Machines
Commutation in a DC machine may be explained as a process

 by virtue of which emf is induced in the armature conductors.
  by which electric current in a coil is reversed.
 how alternate flux affects the main field flux.
  in which magnetic field is set up.

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Electrical Machines
In a stepper motor the detente torque means

  maximum of the static torque with the phase winding excited.
  minimum of the static torque with the phase winding excited.
  maximum of the static torque with the phase winding unexcited.
  minimum of the static torque with the phase winding unexcited.

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