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

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

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Electrical Machines
In a DC machine, for the same value of φ, Z and N; which one of the following statements is correct?

  Armature emf is more with wave winding than with lap winding.
 Armature emf is less with wave winding than with lap winding.
 Armature emf is same as long as the flux density in the air gap remains the same.
 Armature emf depends on weather the machine is running as a motor or generator.

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Electrical Machines
Cogging of induction motor occurs at

 low voltage and when stator and rotor poles are not equal.
 high voltage and when stator and rotor poles are not equal.
 high voltage and when stator and rotor poles are equal.
 low voltage and when stator and rotor poles are equal.

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