(a) Explain what is meant by the back e.m.f. of a motor. (6)

(b) A d.c. motor takes an armature current of 110 A at 480 V. The resistance of the armature circuit is 0.2 Ω. The machine has 6 poles and the armature is lap connected with 864 conductors. The flux per pole is 0.05 wb. Calculate (10)

(a) speed,

(b) the gross torque developed by the armature.