Electrical Machines
The magnetic field which initially induces emf in the armature in a self excited DC generator is because of

 armature reaction.
  residual magnetism.
  permanent magnets.
None of these

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Electrical Machines
Which of the following represents the commutator pitch?

 Number of commutator segments between two successive coils.
 Number of conductors spanned by one coil at the front end of the armature.
 The distance between the staring of first coil and its next successive coil
 Number of conductors spanned by one coil at the back end of the armature.

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Electrical Machines
Consider the following statements : Interpoles in dc machines 1. reducearmature reaction effects in the interpolar region 2. have the same dimension as main polls 3. have their windings connected in series with the armature 4. have same number of turns as the armature 5. have the polarity same as that of the main pole ahead in a motor From these, the correct statements are

 1, 2, 3 and 5
 1, 2 and 3
 1, 3 and 5
 1 and 3

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