72 ELEMENTS OF ELECTRICAL ENGINEERING. 



A graphical representation of the growing current in an inductive circuit im- 

 mediately after a constant electromotive force is applied to the circuit is shown in 

 Fig. 62. 



(t>) If a given current is established in an inductive circuit and the circuit is then 

 closed and left to itself, the current dies away or decays. In this case no electro- 

 motive force acts on the circuit from without, and equation (z') becomes : 





Growing current 

 R=3 ohms 

 L=0.04 henry 

 E=110 volts 



hundredths of a second 



4 5 



Fig. 62. 



Decaying current 

 R=3 ohms 

 It =0.04 henry 

 1=36.7 amperes 



hundredths of a second 



2 3 4 6 78 



Fig. 63. 



The integration of this differential equation under the condition that i = a given 

 value, c7, when t = Q, gives the equation of the decaying current, namely ; 



<=*-*' C4) 



in which e is the Napierian base, and 3 is the given value of the current when 

 t=o. 



A graphical representation of the decaying current in an inductive circuit is shown 

 in Fig. 63. 



