Exam Question

(a) What is back emf. Derive the relation for the back emf and the supplied voltage in terms at armarture reactance (6)

(b) Two earth lamps at 120 V, 15 W are used on a 110 V distribution circuit. Due to damage to a motor, the resistance of the positive line is reduced to 10 ohm and that of the negative line to 5 ohm. Find the voltage across each lamp and the extra load on the generator due to the fault (10)