A. graphite
B. paper
C. mica
D. insulating varnish
A. E/2
B. 2E
C. slightly less than E
D. E
A. copper is harder than mica
B. mica and copper are equally hard
C. mica is harder than copper
D. none of the above
A. ball bearings
B. bush bearings
C. magnetic bearmgs
D. needle bearings
A. flux density
B. reluctance
C. ampere-turns
D. resistance
A. abrasion from dust
B. excessive spring pressure
C. rough commutator bars
D. high mica insulation between com-mutation bars
E. all of the above factors
A. crossmagnetising
B. demagnetising
C. magnetising
D. none of above