Question on determining the back emf generated by the motor...?

Question

A 120.0 volt motor draws a current of 7.80 A when running at normal speed. The resistance of the armature wire is 0.670 ohms.

(a) Determine the back emf generated by the motor.

(b) What is the current at the instant when the motor is just turned on and has not begun to rotate?

(c) What series resistance must be added to limit the starting current to 15.0 A?

Answer 1

A. Eback = Eapplied - I*Rarm
B. I = Eapplied/Rarm
C. Rtotal = Eapplied / I(limit); Radded = Rtotal - Rarm