Electrical Machines
In a 3 - Φ IM in order to eliminate cogging the number of stator slots must be

  unequal to number of rotor slots and skewed in shape.
  either (B) or (C).
  equal to number of rotor slots.
  an integral multiple of number of rotor slots.

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Electrical Machines
In speed control of DC Series motor, speed lower than the rated speed can be obtained by

 Any of the above.
 Connecting an additional resistance in the field circuit.
 Connecting an additional resistance in stator circuit.
 Connecting an additional resistance in the armature circuit.

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