28 



ELEMENTS OF ELECTRICAL ENGINEERING. 



has the same shape as the electromotive force curve if the electro- 

 motive force curve is a curve of sines, but not otherwise ; and even 

 when the electromotive force curve is a curve of sines, the current 

 curve is displaced (shifted along the axis of time) with reference to 

 the electromotive force curve. These voltage-current relations 

 are discussed in detail in Chapter IV. 



When an electromotive force or current curve is a curve of 

 sines the electromotive force or current is said to be harmonic, 

 otherwise the electromotive force or current is non-harmonic. 



Axis 



Fig. 25. 



The full line curve in Fig. 26 represents a non-harmonic elec- 

 tromotive force, and the similarly shaped dotted curve represents 

 the current which the electromotive force produces in a Circuit 

 which contains resistance only. 



The full line curves in Figs. 27 and 28 represent harmonic 

 electromotive forces ; the dotted curve in Fig. 27 represents the 

 harmonic current which the electromotive force produces in a 

 circuit having resistance and inductance ; and the dotted curve 

 in Fig. 28 represents the harmonic current which the electro- 

 motive force produces in a circuit having resistance and contain- 

 ing a condenser. 



It is to be noted that the maximum positive value of a current 

 occurs after the maximum positive value of the electromotive 



