THE DYNAMO. 



37 



rent in the loop of wire and in any outside circuit which is con- 

 nected to the terminals of the loop. An alternating current 

 dynamo is usually called, simply, an alternator. 



A common type of alternator consists of a stationary multipolar 

 electromagnet, called the field magnet, of which the poles N, S, 

 N, S, etc., project radially inwards as shown in Fig. 16 towards 



Fig. 16. 



the passing teeth a, a of a rotating structure A called the arma- 

 ture. On the armature shaft at one end of the armature are fixed 

 two metal rings rr called collecting" rings. These rings are 

 insulated from each other and from the shaft. The ends of the 

 armature wire are connected to these rings as shown, and the 

 wire is wound around the armature teeth in the form of coils, 

 which are shown in section by the dotted squares c, c in Fig. 16. 

 In this type of alternator it is convenient to attribute the induced 

 electromotive forces to the changing of the magnetic flux through 

 the armature teeth and coils as they pass the field poles. As the 

 armature rotates the magnetic flux passes through a given arma- 

 ture coil in one direction when the tooth on which the coil is 



