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 90 cm, a resistance of 25 O, and generates a back emf of 109 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 89 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 throughout the motor? A

Explanation / Answer

a)

wB = 82/102 wA = 0.804 wA

b)

120/50 = 0.24 A

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