reduce the overall mass
insulate core
reduce the eddy current loss
all the above
imperfect contact
severe sparking
rough commutator surface
any one of the above
low voltage, low current
high voltage, high current
low voltage, high current
high voltage, low current
shunt generator
series generator
long shunt compound generator
short shunt compound generator
60-80%
75-85%
80-90%
85-95%