REACTIVE CIRCUITS. 



61 



We therefore have the vector equation of E.M.F.'s 



In 



ri -f kpLi -- ~ = e 



or 



r-i 





(8) 



(9) 



This equation is graphically represented in Fig. 21, where OP 

 is the vector ri, OL the vector - kpLi, 00 the vector -, PQ the 

 vector - (OL 4- OG) t and OQ the vector e. 



FIG. 21. 



If OL is greater than OC, the current lags behind the P.D. by 

 an angle 9, where 



tan = 



f 



If 0(7 is greater than OZ, the current leads before e by an 

 angle given by 



. r\ 

 tan 8 = 



f 



If OL equals (9(7, that is, if 



pL = -^ 

 pC 



the current and P.D. are in phase. 



