CHAPTER IV. 



Capacity in Alternating Current Circuits Combination of Capacity and Induct- 

 ance in series Combination of Capacity and Inductance in Parallel 

 Reactance Resonance Root Mean Square Values. 



CAPACITY IN ALTERNATING CURRENT CIRCUITS. 



22. If a condenser is placed in an alternating current circuit, 

 an alternating current will pass to an extent depending upon the 

 capacity of the condenser and the magnitude and frequency of the 

 P.D. applied between the terminals of the condenser. The result- 

 ing current is the charge and discharge current as the P.D. between 

 the condenser terminals alternates. 



If Q is the quantity of electricity on the condenser at any 

 instant, the current i is the rate of variation of Q and is given by 



Now, by 10, Chap. I., if C is the capacity of the condenser 

 and V the P.D. between its terminals, we have the relation 



Q = CV 

 therefore 



. m dQ 



= C T (2) 



dt 



since C is constant. 



Now, suppose that the P.D. is given by 



F= V Q aio.pt 



Then 



. 



1 = 



= CV Q p sin > + f ..... (3) 



