A circular armature coil is used in a motor with a uniform magnetic field of 2.6

Question

A circular armature coil is used in a motor with a uniform magnetic field of 2.60 T. The coil has a diameter 85 cm, a resistance of 25 , and generates a back emf of 108 VRMS when running a full speed under no load at the angular frequency A.
(A) At what angular frequency, B relative to A does the coil be need to be rotated to generate a back emf of 88 VRMS?

B =  A

(B) If this motor is operating on 120 VRMS now with a load (e.g running a fan) and at the angular frequency A, how much current is flowing throught the motor?

A

Explanation / Answer

part a )

wb/wa = 88/108

wb = 0.8148 wa

part b )

I = (120 - 108)/ 25

I = 0.48 A

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