Electrical Machines
Semi closed slots or totally closed slots are used in induction motors, essentially to

 improve starting torque
 reduce magnetising current and improve power factor
 decrease starting torque
 increase pull out torque

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Electrical Machines
The armature mmf of a DC machine has

  trapezoidal space distribution and is stationary in space.
  triangular space distribution and is stationary in space.
  triangular space distribution and rotates at the speed of armature.
 stepped distribution and rotates at the speed of armature.

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