Electrical Machines
The counter (or back) emf in a dc machine is 1. the same as generated emf in a dc motor 2. proportional to field flux and armature speed 3. not the same as generated emf in a dc motor 4.inversely proportional to field flux 5. proportional to number of armature conductors 6. constant from no load to full load From these, the correct answer is

 1, 2, 5
 2, 4, 5, 6
 2, 3, 6
 3, 4, 5

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Electrical Machines
Which of the following represents the commutator pitch?

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

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

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

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