86 flature'0 



Unit electromotive force (volt) through unit 

 resistance (ohm) gives unit of current (am- 

 pere). It is not the intention to treat the 

 subject mathematically, but I will give you a 

 simple formula for finding the amount of cur- 

 rent if you know the resistance and the volt- 

 age. The electromotive force divided by the 



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resistance gives the current. C = -5 or current 



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(amperes) equals electromotive force (volts) 

 divided by the resistance (ohms). 



But still further: One ampere of current 

 having one volt pressure will develop one watt 

 of power, which is equal to rir of a horse- 

 power. (The watt is named in honor of James 

 Watt, the Scottish inventor of the steam-en- 

 gine 1786-1813). In other words, 746 watts 

 equal one horse-power. By multiplying volts 

 and amperes together we get watts. 



If we want to carry only a small current for 

 a long distance we do not need to use large 

 cells, but many of them. We increase the 

 pressure or voltage by increasing the number 

 of cells set up in series. If we have a wire of 

 given length and resistance and find we need 

 100 volts to force the right amount or strength 

 of current through it, and the electromotive 

 force of the cells we are using is one volt each, 

 it will require 100 cells. If we have a battery 

 that has an E. M. F. of two volts to the cell, 

 as the storage-battery has, fifty cells would 



