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In D.C. machines the residual magnetism is of the order of 2 to 3 percent.

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Description : If residual magnetism is present in a D.C. generator, the induced e.m.f. at zero speed will be?

Answer : If residual magnetism is present in a D.C. generator, the induced e.m.f. at zero speed will be zero.

Description : In dc machines, the armature windings are placed on the rotor because of the necessity for  (1) electromechanical energy conversion (2) generation of voltage (3) commutation (4) development of torque

Answer : 3  Commutation

Answer : In D.C. machines fractional pitch winding is used to reduce the sparking.

Answer : Satisfactory commutation of D.C. machines requires brushes should be of proper grade and size, brushes should smoothly run in the holders, smooth, concentric commutator properly undercut.

Answer : Brushes of D.C. machines are made of carbon.