ELECTRICAL APPLIANCES AND MACHINES 267 



netic field. When the lines of force set up by the primary 

 coil pass around the transformer and into the secondary 

 coil, a current is induced which flows in the opposite 

 direction from that in the primary coil. When the 

 current in the primary coil changes its direction, the lines 

 of force pass around the transformer in the opposite 

 direction from that at first and into the secondary coil, 



ELECTRIC POWER PLANT 



and so a current is set up opposite to the first current in 

 the secondary coil. 



The voltages of the primary and secondary coils have 

 the same ratio as the number of turns of wire in the pri- 

 mary and secondary coils. If the voltage in the primary 

 is 2 200 and the number of turns of the primary on the 

 transformer is 4400, the voltage in the secondary will 

 be no if the turns of the secondary on the transformer 

 are 220. Transformers are usually enclosed in metal 

 cases which can be seen on poles carrying electric light 

 wires. 



