4-A] SERIES AND PARALLEL CIRCUITS. 121 



cuits by writing I -r- Go in place of Lo>, and reversing the diagrams 

 (as in a mirror) so that current is leading instead of lagging. 



Inductance produces effects similar to mass in a moving mech- 

 anism; capacity produces effects similar to a spring. Inductance and 

 capacity store, but do not consume,* energy; the stored energy being 

 JL.T in inductance and JCE 2 in capacity. 



56. As frequency is increased, the impedance of an inductive cir- 

 cuit becomes greater; the impedance of a capacity circuit becomes 

 less. Furthermore, as frequency is increased, in an inductive circuit 

 becomes greater; in a capacity circuit becomes less. 



57. Circuits with Inductance and Capacity. When a circuit con- 

 tains both inductance and capacity, the total reactance of the circuit 

 is the difference between the inductive reactance and the capacity 

 reactance ; X = Lo> i/Cw. Inductance and capacity tend to neu- 

 tralize each other. When the inductive reactance is greater than the 

 capacity reactance, the current lags behind the electromotive force, 

 as in an inductive circuit ; when, on the other hand, the capacity react- 

 ance is the greater, the current is in advance of the electromotive 

 force, as in a capacity circuit. In either case, tan = X -=- R. 



58. Voltage Resonance. In a series circuit, the total impedance 

 may, therefore, be less than the impedance of part of the circuit only, 

 and the total impressed voltage may, accordingly, be less than the 

 voltage drop around part of the circuit only. The voltage around 

 part of the circuit is thus increased by resonance so as to be greater 

 than the impressed electromotive force. 



59. Current Resonance. In parallel circuits with two branches, 

 one with inductance and the other with capacity, the current in the 

 inductance branch is lagging while the current in the capacity branch 

 is leading. The two branch currents are to a certain extent in phase 

 opposition so that the total or main line current, which is the vector 

 sum of the two, may be less than the current in either branch. 

 Due to resonance, a local circulating current is obtained which is 

 greater than the current from the generator. 



60. Non-Sine Waves. When the impressed electromotive force 

 does not follow a sine law, there are present in addition to the 



* In an inductance with iron, some energy is lost in magnetic hysteresis ; 

 similarly, in a condenser, a small amount of energy is lost in dielectric 

 hysteresis. 



