A circular armature coil is used in a motor with a uniform magnetic field of 4.3

Question

A circular armature coil is used in a motor with a uniform magnetic field of 4.30 T. The coil has a diameter 85 cm, a resistance of 30 ?, and generates a back emf of 91 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 71VRMS?

(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?

Explanation / Answer

A. 71/91 = 0.78

B. (120 - 91)/30 = 0.967

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