4 -A] SERIES AND PARALLEL CIRCUITS. 115 



40. From these electromotive forces, we have the definitions : 



Impedance is total electromotive force divided by current; 

 Z = E-+-L 



Resistance is power or in-phase component of electromotive 

 force divided by current; R = E cos -f- /. (In general, when 

 motors, transformers, etc., are included in the circuit, this gives 

 apparent resistance.) 



Reactance* is the wattless or quadrature component of electro- 

 motive force divided by current ; X = E sin 6 -=- /. 



41. Components of Current.^ In a similar manner, the cur- 

 rent may be resolved into a power component, 7p 7cos0, in 

 phase with E, and a wattless component /Q = /sin0, in quadra- 

 ture with E ; the total current is /= V^? 2 + ^Q 2 * 



42. From these currents, we have the definitions : 



Admittance Y is total current divided by electromotive force; 

 Y = I-^E. 



Conductance g is the power or in-phase component of current 

 divided by electromotive force; g = Icos6-r-E. 



Susceptance b is the wattless or quadrature component of cur- 

 rent divided by electromotive force; b = I smB-^-E. 



We have, then, the following relations; 



Total current = I = E X Y. 

 Power current = / cos E X & 

 Wattless current = 7 sin 6 = E X b. 

 g=YcosO. 



Admittance = V<7 



*This is the general definition, Lw, i/Cw, etc., being merely particular 

 values; see paper on Reactance, by Steinmetz and Bedell, p. 640, Vol. 

 XL, Transactions A. I. E. E., 1894. 



t (4ia). As an illustration of the resolution of current, see Fig. 2 and 

 other figures in Exp. s-C. It is usual to resolve electromotive force into 

 components for series circuits and current into components for parallel 

 circuits. 



