1. (a) Explain what is meant by the term ‘back e.m.f.’ in a motor. (b) Outline the basic differences between series, shunt and compoundwound d.c. motors. 2 .(a) With the aid of diagrams explain how...

1. (a) Explain what is meant by the term ‘back e.m.f.’ in a motor. (b) Outline the basic differences between series, shunt and compoundwound d.c. motors. 2 .(a) With the aid of diagrams explain how the speed of series, shunt and compound-wound motors may be controlled. (b) A 440 V d.c. shunt-wound motor has a field resistance of 200 and an armature resistance of 0.6 . When its speed is 20 revs/second the current drawn from the supply is 12.2 A. Calculate its back e.m.f. at this speed. If the speed were decreased to 19 revs/second, the field flux remaining unchanged, calculate the new back e.m.f. and the new armature current.