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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Electrical Machines
Interpoles in a DC motor must be

 Shunt excited and should have the same polarity as that of the ahead main pole in the direction of rotation of armature.
 Series excited and should have the same polarity as that of the ahead main pole in the direction of rotation of armature.
 Shunt excited and should have the same polarity as that of the behind main pole in the direction of rotation of armature.
 Series excited and should have the same polarity as that of the behind main pole in the direction of rotation of armature.

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