A circular armature coil is used in a motor with a uniform magnetic field of 4.4

Question

A circular armature coil is used in a motor with a uniform magnetic field of 4.45 T. The coil has a diameter 100 cm, a resistance of 25 ?, and generates a back emf of 107 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 87 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

A) wB = 87/107 = 0.813

B) I = (120 - 107) / 25 = 0.52 A

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