Electricity 



223 



circuit through the laboratory switches. 



is to make it clear that electricity can flow only through 

 a complete circuit ; it must have an unbroken path from 

 the dynamo back to the dynamo again or from one pole 

 of the battery back to the other pole. If the electricity 

 does not have a complete circuit, it will not flow. 



Application 52. A small boy disconnected the doorbell 

 batteries from the wires that ran to them, and when he 

 wanted to put the wires back, he could not remember how 

 they had been connected. He tried fastening both wires 

 to the carbon part of the battery, connecting one wire to 

 the carbon and one to the zinc, and connecting both to the 

 zinc. Then he decided that one wire was all that had to be 

 connected anyway, that the second was simply to make it 

 stronger. Which of the ways he tried, if any, would have 

 been right? 



Circuit A Circuit B 

 FIG. 125. Parallel circuits. 



Circuit G 



