Electrical Machines
With the increase in speed of a DC motor

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

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Electrical Machines
Which of the following factors improve commutation in a dc machine ? 1. High contact resistance of brushes 2. High inductance of the coils undergoing commutation 3. Shifting of brushes in the direction of rotation for a generator and in the opposite direction For a motor 4. Narrow width for the commutation bars Select the correct answer using the codes given below : Codes :

 2, 3 and 4
 1, 2 and 4
 1 and 3
 1, 2, and 3

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