Answer : Open circuited armature coil of a D.C. machine is identified by the scarring of the commutator segment to which open circuited coil is connected and indicated by a spark completely around the commutator.
Answer : In a D.C. machine stray loss is the sum of iron loss and mechanical loss.
Answer : To avoid formation of grooves in the commutator of a D.C. machine the brushes of opposite polarity should track each other.
Answer : In case of D.C. machine winding, number of commutator segments is equal to number of armature coils.
Answer : Iron losses in a D.C. machine are independent of variations in load.