A circular armature coil is used in a motor with a uniform magnetic field of 2.1

Question

A circular armature coil is used in a motor with a uniform magnetic field of 2.15 T. The coil has a diameter 85 cm, a resistance of 50 ?, and generates a back emf of 98 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 78 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 =(78/98) = 0.796*wA

B)

current flowing = (120 -98)/50 = 0.44 A

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