Electrical Machines
The speed of a DC series motor is

 Proportional to field current.
 Inversely proportional to the armature current.
 Proportional to the square of the armature current.
 Proportional to the armature current.

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Electrical Machines
The introduction of interpoles in between the main poles improves the performance of a dc machine, because

 the inequality of air-gap flux on the top and bottom halves of the armature is removed
 the flux waveform is improved with reduction in harmonics
 the interpoles produce additional flux to augment the developed torque
 a counter-emf is induced in the coil undergoing commutation

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Electrical Machines
Flashing of DC generator means

None of these
  increasing flux density by providing extra ampere-turns in field.
  creation of residual magnetism by a DC source.
 neutralization of residual magnetism.

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