A circular armature coil is used in a motor with a uniform magnetic field of 2.3

Question

A circular armature coil is used in a motor with a uniform magnetic field of 2.30 T. The coil has a diameter 95 cm, a resistance of 30 O, and generates a back emf of 97 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 77 VRMS?
?B = ?A

(B) If this motor is operating on 120 VRMS with a no-load angular frequency ?A, how much current is flowing throught the motor?
A

Explanation / Answer

a)

= A B cos

= d/dt = AB sin d/dt = AB sin

>>>> B/A = B/A

>>>> B/A = 77/97 = 0.794

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b)

i = V/R = 120/30 = 4 A

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