CoachThe period of an alternating voltage is the duration of one complete cycle — one full swing up, down and back, in seconds. Its frequency is the number of cycles per second, in hertz — sound’s unit, serving again — and the two are each other’s reciprocals:
示例
Example 67.4 (Frequency arithmetic)
The reciprocal pair computes both ways. A generator cycling at : — seventeen milliseconds. An oscilloscope shows a cycle lasting : . A bicycle dynamo at slow pedaling makes : period a tenth of a second — and its lamp visibly flickers, ten pulses to the second, until speed smooths them beyond the eye’s noticing.