RESISTANCE AND ELECTROMOTIVE FORCE. 45 



connected in series. When two portions of an electrical circuit 

 are so connected that the current in the circuit divides and part 

 of it flows through each portion, the portions are said to be con- 

 nected in parallel. Thus, Fig. 20 shows two lamps L and L' 





_ > 



Fig. 20. Fig. 21. 



connected in series, and Fig. 21 shows two lamps connected in 

 parallel. 



The ordinary arc lamps which are used to light city streets are 

 connected in series, and the entire current delivered by the light- 

 ing generator flows through each lamp. On the other hand, if 

 the electromotive force of the generator is, say, 2,000 volts and 

 if there are 40 similar * lamps in series, the electromotive force 

 between the terminals of each lamp will be 50 volts. The electro- 

 motive force of a generator is subdivided among a number of lamps 

 or other units connected in series. 



The ordinary glow lamps which are used for house-lighting are 

 connected in parallel between copper mains which lead out from 

 the terminals of the generator, and, except for a slight drop of 

 electromotive force in the mains, the full electromotive force of 

 the generator acts upon each lamp. On the other hand, if the 

 generator delivers, say, 1,000 amperes and if there are 2,000 simi- 

 lar * lamps connected between the mains, the current in each lamp 

 will be one half ampere. The current delivered by a generator is 

 subdivided among a number of lamps or other units connected in 

 parallel. 



Voltaic cells are often connected in series. When this is done 

 the electromotive force which is available for the maintenance of 

 current is equal to the sum of the electromotive forces of the indi- 



* Having the same resistance.- 



