ELECTRIC MOMENTUM. INDUCTANCE. 151 



in volts by the value i in amperes (equals Ri z ~) which gives 160 

 watts. 



The ordinates of the curve in Fig. 98 represent the successive 

 values of a decaying current in a circuit of which the resistance 



Decaying cuireut 

 R=3 ohms 

 L=O.04 henry 

 .1=36.7 amperes 



hundredth* of a second 



2. f S, 6 7 8 



Fig. 98 



is 3 ohms and the inductance is 0.04 henry, the initial value of 

 the current being 36.7 amperes. 



The equation of the curve of decaying current in Fig. 98 is 



*>/-*' (54)* 



in which is the Naperian base, / is the value of the decaying 

 current at the instant from which time is reckoned, and i is the 

 value of the decaying current / seconds later. 



80. The choke coil. A coil having considerable inductance is 

 frequently used for the choking of rapid fluctuations of current. 

 Such a coil is called a choke coil. When a choke coil is connected 

 to the terminals of an alternator the rapidly alternating electro- 

 motive force of the alternator produces but little current through 

 the coil. This is analogous to the fact that a rapidly alternating 



* Equations (52) and (54) are obtained by integrating the differential equations 

 (51) and (53) with due reference to the known value of the current at the instant 



