A 200-V dc shunt motor has a field resistance of 200 and an armature resistance of 0.5 . On no load, the machine operates with full field flux at a speed of 1000 r/min with an armature current of 4 A. Neglect magnetic saturation and armature reaction.
(a) If the motor drives a load requiring a torque of 100 N · m, find the armature current and speed of the motor.
(b) If the motor is required to develop 10 hp at 1200 r/min, compute the required value of external series resistance in the field circuit.