44 TREATISE ON ALTERNATING CURRENTS. 



to balance this is therefore given by OL', where OL' = OL. The 

 maximum value, E, of the P.D. is therefore given by OE, the 

 diagonal of the parallelogram L'OAE. 

 Thus 



or 



E 



Also the current lags behind the P.D. by an angle 9 where 



Therefore, if the P.D. is given by c = E sin pt, the current is 

 given at any instant by 



E sin (pt 0) 



r* + pi? 



which is the same as equation (11) Chap. III., which was obtained 

 by other means. 



The instantaneous values of c and ri are given by the lengths 

 of the perpendiculars drawn from the points E and A to the base 

 line as the rectangle OAEL' revolves about 0. 



