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 95 cm, a resistance of 35 , 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?

Explanation / Answer

A) you'll just want to take the rotated emf value (smaller Vrms) and divide it by the given back emf of the coil at full speed under no load at A (larger Vrms).

B = 82/102 = 0.804

B) just take the 120 Vrms and subtract the A emf value at full speed under no load and then divide by the resistance.
The current flowing throught the motor = (120-102)/35 = 0.514 A

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