INDUCED CURRENTS 159 



for the motors of some electric car systems alternatr 

 ing currents are employed. Direct currents are used in 

 electrolysis, electroplating and electro typing, for many 

 motors, etc. 



184. The Transformer The current that supplies 



small electric lamps in many houses and other buildings 

 has to be of high potential (great electro-motive force) in 

 order to travel through the long circuit. But such a 

 current might prove danger- 

 ous if used freely in houses. 

 To lessen the danger and still 

 keep up the flow, a transformer 

 is employed. 



A transformer consists of 

 a coil of long, fine insulated 

 wire, surrounded by a coil 

 of short, coarse insulated wire 

 (Fig. 116). The high-potential 

 alternating current from the 



dynamo being passed through 

 , , . FIG. no 



the long, fine wire coil, an 



alternating current is set up in the coarser wire by 

 induction. This current has greater strength than that 

 from the dynamo, but it has a lower potential. From 

 the coarse wire coil, then, this low-potential current is 

 led to the building where it is used. Because of its 

 lower potential it is less dangerous. 



For some purposes it may be desired to change a cur- 

 rent of great strength but low potential into a current 

 of less strength and high potential. To do this the 



