ELECTRICAL PRESSURE 



363 



rapidly. The reason for this is that the longer wire offers 

 greater resistance to the current, so that less current flows ; 

 but as in the case of the tank of water, the current will 

 flow for a longer time. 



You also know that a pipe of large diameter will empty 

 a tank of water much quicker than one of small diam- 

 eter. A large tube (or pipe) carries a larger current of 

 water than a small one. Just so with electric currents. 



Pipe 



(low resistance) I/or^PipeGnghresistaT 

 Heavy "Flow 



Short Wire I/ongWire, 

 (low resistance) ("high, resistance 

 j Large 3m a 11 



Water analogy: short and long wire resistance. 



The wire with a large diameter permits a larger flow of 

 electricity than one of small diameter. 



Electrical pressure. Suppose you have two tanks of 

 water, one holding a large amount, and the other a small 

 amount and that the water in them is kept at the same 

 level. The water running from the faucets at the bottom 

 will have the same pressure just so long as the level is 

 maintained evenly in the two, and if the openings of the 

 two faucets are of the same size, equal streams or currents 

 of water will flow from them. The electrical pressure 

 (called voltage) is independent of the size of the cells used. 

 The cell of a small flashlight may have just as high pres- 

 sure or voltage as does a common dry cell which has a 



