11.Brushes of D.C. machines are made of

12.The bearings used to support the rotor shafts are generally

13.For a D.C. generator when the number of poles and the number of armature conductors is fixed, then which winding will give the higher e.m.f. ?

14.In D.C. generators, the cause of rapid brush wear may be

15.In case of a 4-pole D.C. generator provided with a two layer lap winding with sixteen coils, the pole pitch will be