A circular armature coil is used in a motor with a uniform magnetic field of 2.8

Question

A circular armature coil is used in a motor with a uniform magnetic field of 2.80 T. The coil has a diameter 65 cm, a resistance of 30 , and generates a back emf of 110 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 90 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

On part 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).

On part B just take the 120 Vrms and subtract the A emf value at full speed under no load and then divide by the

resistance.

So

, for (A):

B =90/110

B =0.818A

And for (B):

the current is flowing throught the motor =(120-110)/30 = 0.96

=0.33 A

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.