Electrical Machines
In dc machines, 1. reactance voltage is proportional to armature current 2.reactance voltage is proportional to core length 3.reactance voltage is due to self-flux of the coil undergoing commutation 4. armature-cross flux is neutralized by interpolar flux 5. interpolarmmf is more than armature mmf in the interpolar zone From these, the correct answer is

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

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Electrical Machines
With the increase in speed of a DC motor

 both back emf as well as line current fall.
 back emf increases but line current falls.
 back emf falls and line current increases.
 both back emf as well as line current increase.

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Electrical Machines
Cogging in induction motor occurs when

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

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