(a) Explain the effect of changing current and its associated magnetic flux on the induced e.m.f (6)

(b) A d.c. generator gave the following O.C.C. when driven at 1000 rev/min.

Field Current (A) 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6

Armature Voltage (V) 32, 58, 78, 93, 104, 113, 120, 125

If the machine is run as a shunt generator at 1000 rev/min, the shunt-field resistance being 100Ω, find

(i) the O.C. voltage

(ii) the critical value of the shunt-field resistance,

(iii) the O.C. voltage if the speed was raised to 1100 rev/min, the field resistance being kept constant at 100Ω.