82 



ELEMENTS OF ELECTRICAL ENGINEERING. 



condenser starts out with the value ejR at the very instant at 

 which the electromotive force begins to act. These effects are 

 shown in Fig. 74 ; AA is the electromotive force curve (current 

 curve in a non-inductive circuit), CC is the current produced by 

 AA in an iron-less inductance, and BB is the current produced 

 by AA in a condenser. The inequalities of the first two or 



Fig. 74.* 



three positive and negative half- waves in curve CC illustrate the 

 effects described* in Art. 33 (Fig. 65), and the extremely sharp 

 peak in curve BB at the instant of connecting illustrates the 

 effect of a condenser. The curve AA is upside down, that is, 

 the oscillograph which traced curve AA should have had its 

 connections reversed. 



38. Current loci. In some practical problems, for example in the analysis of the 

 action of the transformer and of the induction motor, it is necessary to consider the man- 

 ner in which the current varies in value and in phase: (a] When the resistance of 

 the circuit is constant and the reactance is changed slowly from zero to an indefinitely 

 large value, and (b] When the reactance of the circuit is constant and the resistance is 

 changed slowly from zero to an indefinitely large value ; the electromotive fl5rce hav- 

 ing a constant (effective) value and a constant frequency in each case. 



*The photographs from which Figs. 71, 72, 73 and 74 are reproduced were 

 kindly furnished to the authors by the General Electric Company. 



