THE ALTERNATOR. 



2 9 



force in Fig. 27, and before the maximum positive value of the 

 electromotive force in Fig. 28. This is usually expressed by 

 saying that the current lags behind the electromotive force in a 

 circuit having resistance and inductance, and that the current leads 



Fig. 26. Circuit containing resistance only. 



or is ahead of the electromotive force in a circuit having resistance 

 and containing a condenser. 



A harmonic electromotive force does not always, however, pro- 



7 



Axis 



time 



Fig. 27. Circuit having resistance and inductance. 



duce a harmonic current. Thus Fig. 29 shows a harmonic elec- 

 tromotive force, and the current which this electromotive force 

 produces in a coil of wire wound on an iron core. 



