MNA (magnetic neutral axis)

GNA (geometric neutral axis)

perpendicular to MNA

perpendicular to GNA

reactance voltage generated as a consequence of commutation

cross-magnetising the effect of armature reaction

demagnetising effect of armature reaction

all the above

rate of change of flux is minimum

rate of change of flux is maximum

flux linked with conductors is maximum

flux linked with conductors is minimum

to increase the resistance of brushes

to reduce the no. of turns in the armature coil so as to reduce the no. of commutator segments

to neutralise the reactance voltage by producing a reversing e.m.f. in the short-circuited coil under commutation

all the above

to neutralise the reactance voltage to help commutation process

to neutralise the cross-magnetising effect of armature reaction

to reduce sparking at the commutator

all the above