DIYbanter - View Single Post

wrote:
If the low peak of the sine wave (and the rest of the the sine wave for
that matter) is "fully" above the "zero" reference point, then isn't it
true that the current DOES NOT alternate? That is to say, that current
only flows in one direction....i.e. "direct current"? Isn't it also
true that if the low peak of the sine wave is -0.00001V then the sine
wave results in current flowing in both direction (albeit for a
nanosecond)....i.e. "alternating current".....I'm not arguing that my
use of nomenclature is "pure" or conventional....but I don't see how it
is fundamentally wrong, without merit, or lacking a reasonable
basis.....

You seem very attached to the word, "alternating" that is abbreviated
in the term AC. Once people get involved in analyzing circuits and
waveforms, they start to think in terms of frequencies. All kinds of
signals can be described in terms of the frequencies they contain.
Signals with zero frequency are analyzed and described as DC, while
everything else is some frequency other than zero. And there are two
distinct kinds of frequency. One is based on number of sinusoidal
cycles in a given period of time and the other is based on exponential
decay or growth rate (number of decay or growth time constants per
time period).

I am sure that many who have not learned the math of Laplace
transforms have a hard time thinking of a decaying, unidirectional
pulse as a kind of frequency, since it never alternates, but there are
such powerful analytical reasons to take this view that anyone who
understands this power has little difficulty with this rather non
literal extension of the AC frequency concept.

So only those with a very primitive view of frequency and are bothered
by describing a non alternating but time varying signal as a kind of
frequency (and informally called AC). The simple minded terms, AC and
DC are just not up to the job of describing many waveforms, unless you
are willing to be quite flexible in the usage.