A circular armature coil is used in a motor with a uniform magnetic field of 4.1

Question

A circular armature coil is used in a motor with a uniform magnetic field of 4.10 T. The coil has a diameter 60 cm, a resistance of 50 ?, and generates a back emf of 102 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 82 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)

NBAwA = V

So, wB =(88/108) 0.815*wA <----answer....here wB = angular frequency of B , wA =ang frequency of A.

B)

current flowing = (120 -108)/25 = 0.48 A <------answer

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