ALTERNATING CURRENTS 



a two-pole machine one space-degree is the same as one electrical 

 time-degree. 



When the voltage has completed only half a cycle or 180, 

 it has gone through one alternation. 



Assume that the coil in Fig. 1 is 

 making 60 revolutions per second, 

 or 3,600 r.p.m. Sixty complete 

 cycles will be generated each 

 second. Therefore, a two-pole, 

 60-cycle generator must have a 

 speed of 3,600 r.p.m. 



The abscissas may be graduated 

 in time as well as in degrees. For example, Fig. 5, jthe time 

 corresponding to 360 is J^JQ sec. and the time corresponding 



Fio. 5. Sine wave as a function 

 of time. 



to 180 is K20 sec. 



Alternating-current waves may be plotted with either time 

 or degrees as abscissas. 



Fio. 6. Two cycles per revolution in 4-pole alternator. 



Figure 6 (a) shows a four-pole machine. A single conductor a 

 of a coil is shown rotating, rather than the complete coil. As 

 soon as this conductor has passed a north and a south pole, that 



