Electrical Machines
In a DC generator, the armature reaction results in

  demagnetization of leading & magnetization of trailing pole tip.
 magnetization of leading and demagnetization of trailing pole tip.
  magnetization of inter poles.
 demagnetization of centers of poles.

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Electrical Machines
Cogging in induction motor occurs when

 number of stator teeth - number of rotor teeth = odd number.
 number of stator teeth - number of rotor teeth = even number.
 number of stator teeth - number of rotor teeth = negative number.
 number of stator teeth - number of rotor teeth = 0.

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Electrical Machines
A dc shunt generator, when commissioned after a major repair of the field system, failed to build Up voltage. It was because

 there was a break in the armature circuit
 field winding was wrongly connected
 field system lost residual magnetism
 field resistance was higher than critical resistance

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