Electrical Machines
The squirrel cage induction motors are provided with blades in order to

  balance the rotor dynamically.
  eliminate noise.
  none of these.
  facilitate cooling of rotor.

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

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