Transportation on Land 



325 



143. The principle of the generator. We may illustrate 

 the principle of the generator very simply, as we did in the 

 case of the motor. When the end of a permanent magnet is 

 moved across a wire as in Fig. 103, there is 

 generated in the wire an electric current. 

 The current produced by a magnet moving 

 across a single wire is necessarily very weak ; 

 but it shows exactly what is' done in the 

 actual generator. 



If a very long, fine, insulated wire is 

 wound into a coil like that in Fig. 104, and 

 made to whirl rapidly between the ends of 

 a U magnet so that the wire is near both 

 ends simultaneously, there will be produced 

 an electric current of considerable pressure. 

 The current may be taken off the collectors 

 (C, C), which in the generator, as in the 

 motor, form the commutator, by means of brushes (B, B), and 

 measured by a galvanometer connected in the circuit or 

 made to produce a spark. The coil ;of wire represents the 

 armature, and the magnet represents the field magnet. 



FIG. 103. A mag- 

 net moving across the 

 single wire toward 

 the observer induces 

 in the wire an electric 

 current. This is the 

 simplest form of the 

 electric generator. 



N 



FIG. 104. A simple generator of electric current ; a single wire loop 

 (armature) turning in a magnetic field (N, S), direction of the electric current 

 indicated by arrows, split ring commutator (C, C) and brushes (B, B). 



