MAGNETIC EFFECTS OF ELECTRIC CURRENTS 237 



electricity. The voltage on the first circuit is 110 volts, that 

 on the second is about 11 volts. This information gives us 

 a hint for naming the device a transformer. The voltage 

 is transformed, " stepped down," or " changed over " from 

 110 volts to 11 volts. 



243. Uses of the transformer. A full explanation of the 

 transformer by means of which the reduced voltage is secured 

 must be reserved for the later course in physics. However, 

 we may say that as the current alternates 120 times (60 com- 

 plete changes) per second in the 110-volt coil, the reversals 

 of the current cause the lines of magnetic force to swing 

 back and forth through the 11-volt coil, causing an alternat- 

 ing induced current to pass through the coil and its circuit. 

 The core of steel concentrates the lines of force about the 

 coils. The transformer, then, is a device which makes use 

 of the magnetic field about an electromagnet. 



Large transformers are used to distribute the electric 

 currents to the community. Such transformers are com- 

 monly seen fastened to posts in streets and alleys. Two ter- 

 minals of the high-voltage coil of relatively small wire are 

 shown (fig. 120). The low-voltage coil is wound in two sec- 

 tions, giving four terminals as shown on the front of the 

 case in the figure. These coils can be connected so as to 

 give 110 or 220 volts. The wires of the secondary coils 

 (110-220 volts) are larger than those in the primary coils 

 (1100-2200 volts), and this indicates that heavier currents 

 pass through them. The transformer is merely a device for 

 trading volts for amperes, or vice versa; that is, when the 

 voltage is high the current will be low, when the current is 

 large the voltage will be small. 



There are many different styles of transformers adapted 

 for domestic and commercial use. They range in size from 

 the small bell-ringing transformers to the huge transmission 

 transformers housed in large power plants. There are dis- 

 tributing transformers of all sizes, sign-lighting transformers, 



