42 



ALTERNATING CURRENTS 



in phase with each other. Under these conditions the condensive 

 current must be equal to the inductive current. These two 

 being opposite and equal balance each other, leaving only the 

 resistance current. This is illustrated in Fig. 40 (a). E is the 

 voltage wave; I R is the current in the resistance; IL is the current 

 in the inductance; I c is the current in the condenser and is equal 

 to I L . As the inductive current lags the voltage by 90 and the 

 condensive current leads the voltage by 90, they are in direct 

 opposition and being equal, they balance. This leaves only I R . 



Fio. 40. Resonance in a parallel circuit. 



Figure 40 (6) illustrates vectorially these circuit conditions. 

 It will be observed that the total current is a minimum when the 

 parallel circuit is in resonance, whereas in the series circuit, 

 the current is a maximum at resonance. In the parallel circuit 

 the inductive and condensive currents are opposite and equal; 

 in the series circuit the inductive and condensive voltages are 

 opposite and equal. If a pure capacitance and a pure induc- 

 tance were connected in parallel and adjusted for resonance, 

 the line current would be zero, even though the inductance and 

 condenser were each taking current. 



