Question

carbon brushes in an electric motor ar used to
a)increase efficiency
b)brush the commutator
c)reverse current
d)decrease resistance

Answer 1

so far i know, they brush the commutator and reverse the current

Answer 2

Reverse the current, yet maintain the valuable contact with the armature. (other wise if we used plain wires, the whole system of wires would twist up and seize. STALL! :p)

Answer 3

b)