EFFECTS OF CAPACITY. 31 



or by (1) 



fj / ft 7* *? 



From this we find that when the current has reached a steady 

 periodic state its value is given by (see Appendix) 



where 



pL -- - n 

 pC 

 tan ^ = -- ~ 



This shows that the current lags behind or leads before the 

 E.M.F., according as pL is greater or less than ^. If pL = ^ 

 the self-induction and capacity exactly balance each other. 



The quantity pL -- ~ is called the Reactance of the circuit. 



In an inductive circuit the reactance is positive ; in a circuit con- 

 taining capacity only it is negative ; in a circuit containing both 

 inductance and capacity it is positive or negative according as ^L 



is greater or less than ^ 



When a circuit contains both inductance and capacity in such 

 proportion that the reactance is zero, we have the phenomenon of 

 electrical Resonance. 



25. Electric Currents in Parallel Circuits, one 

 Branch of which contains Resistance and Self- 

 induction and the other Resistance and Capacity. 

 Let TI and L be the resistance and self induction in one branch, 

 and r 2 and C the resistance and capacity in the other branch. Let 

 ii, i% be the currents in the two branches and v = Fsin pt the 

 common P.D. between their terminals. 



The equation for the inductive branch is 



and that for the capacity branch is 



+- = Vsinpt ..... (11) 



