ELECTRIC CIRCUITS 131 



83. Circuit Constants. A continuous-current circuit has two 



constants, 



impressed e.m.f. 



resistance R, r = - > 



current 



current 



conductance G, g = -. 5 -- j- > 

 impressed e.m.f. 



and the conductance is the reciprocal of the resistance or 



Continuous-current circuits also have inductance and electro- 

 static capacity, but these do not affect the flow of current except 

 at the instant of opening or closing the circuit. 



An alternating-current circuit has six so-called constants, 



(1) resistance R, r, 



(2) reactance X, x, 



(3) impedance Z, z, 



(4) admittance Y, y, 



(5) conductance G, g, 



(6) susceptance B, b. 



(1) The resistance of a circuit consumes a component of e.m.f. 

 in phase with the current and so consumes power. In circuits 

 which are partially inclosed in iron an alternating magnetic flux 

 is produced in the iron and a loss of power occurs due to hysteresis 

 and eddy currents. These iron losses are sometimes included 

 with the copper loss and charged against the resistance. This 

 gives a value of resistance greater than the true ohmic resistance 

 and is called the effective resistance of the circuit. Since the 

 hysteresis and eddy current losses vary both with the frequency 

 and the induction density in the iron, the effective resistance is 

 not a constant quantity. 



The power component of the impressed e.m.f. or the component 

 in phase with the current is 



#1 = IR, 

 and the resistance is 



n _ EI _ power component of impressed e.m.f. 

 I current 



in-phase component of impressed e.m.f. ( . 



- . . (17o) 

 current 



