i 4 ALTERNATING CURRENTS 



The diagram of Fig. 10 has been drawn on the supposition that 



the reactance L due to inductance exceeds the reactance ?r- due to 



Gp 



capacity. In this case, is positive, i.e. the current lags behind the 

 impressed e.m.f. ; is frequently spoken of as the angle of lay. It 



may, however, happen that ~- > Lp, 9 then becoming negative, i.e. 

 the current leading instead of lagging. 



FIG. 10. Vector Diagram for Inductive Resistance in Series with Capacity. 



We may, further, consider the special case in which ~Lp = ~ ; now 



vanishes, i.e. the current comes into phase with the impressed e.m.f., 

 and the impedance becomes simply equal to the resistance. The 

 current is, therefore, the same as that which would be obtained with 

 the same impressed e.m.f. in a non-inductive circuit of resistance r. 

 Under these very special circumstances, the circuit is said to exhibit 

 electrical resonance or syntony ; the effect due to self-inductance being 

 completely neutralized by that due to capacity. 



When electrical resonance occurs in a highly inductive circuit, 

 i.e. one whose self-inductance is very large in comparison with its 

 resistance, we have the very remarkable result that the p.d.'s across 

 the inductive resistance and the condenser may very largely exceed 

 the impressed e.m.f. This is at once evident from the vector diagram 



