Little bits of a cycleEngineers break the ac cycle down into small parts for analysis and reference. One com-plete cycle can be likened to a single revolution around a circle.DegreesOne method of specifying the phase of an ac cycle is to divide it into 360 equal parts,called degrees or degrees of phase. The value 0 degrees is assigned to the point in thecycle where the magnitude is 0 and positive-going. The same point on the next cycle isgiven the value 360 degrees. Then halfway through the cycle is 180 degrees; a quartercycle is 90 degrees, and so on. This is illustrated in Fig. 9-9.172 Alternating current basics9-9A cycle is divided into 360 degrees.RadiansThe other method of specifying phase is to divide the cycle into 6.28 equal parts. This isapproximately the number of radii of a circle that can be laid end-to-end around the cir-cumference. A radian of phase is equal to about 57.3 degrees. This unit of phase issomething you won’t often be needing to use, because it’s more common among physi-cists than among engineers.Sometimes, the frequency of an ac wave is measured in radians per second, ratherthan in hertz (cycles per second). Because there are about 6.28 radians in a completecycle of 360 degrees, the angular frequency of a wave, in radians per second, is equalto about 6.28 times the frequency in hertz.