Fig. 180.
Fig. 181.
The Alternating System, Fig. 181, uses transformers. The high potential of the current allows small main wires, from which branches can be run to the primary coil of the transformer. The secondary coil sends out an induced current of 50 or 110 volts, while that in the primary may be 1,000 to 10,000 volts.
CHAPTER XX.
HOW HEAT IS PRODUCED BY THE ELECTRIC CURRENT.
145. Resistance and Heat. We have seen that all wires and conductors offer resistance to the electric current. The smaller the wire the greater its resistance. Whenever resistance is offered to the current, heat is produced. By proper appliances, the heat of resistance can be used to advantage for many commercial enterprises. Dynamos are used to generate the current for heating and lighting purposes.
Fig. 182.