ALTERNATING CURRENTS 



and 



= - * cos 



These new values of y\ and y 2 

 dotted curve representing [yi] t = 



Mf.tr 



From this we see that during a time interval -J-T each curve has, 

 without altering its size or shape, been displaced through a distance 



are also shown in Fig. 30, the 

 and the chain-dotted curve 



FIG. 30. Rotating Waves of Flux. 



= JA, and that the displacement for y\ has been a forward one, and 

 that for y% a "backward one. Hence y\ and y< represent two waves 

 of magnetic flux travelling without change of size or shape in opposite 

 directions around the rotor periphery. We speak of such a travelling 

 or moving wave of magnetic flux as a rotating wave of flux or a 

 rotating magnetic field, and the result just established shows that 

 a simple alternating or stationary wave is equivalent to, en" may be 

 replaced by, two rotating waves. 



The directions of rotation corresponding to y\ and y z are indicated 

 by the dotted and chain-dotted arrows respectively in Fig. 30. By 

 adding the ordinates of [yi]j_i T and [2te]j_, T we, of course, obtain 

 the ordinates of the curve corresponding to [y\ t _ , T in Fig. 29. 



It will be noticed that the amplitude of each of the two component 

 rotating waves is equal to half the maximum amplitude of the 

 resultant alternating or stationary wave. 



The relation just established between an alternating wave and 



