Wednesday, 8 January 2020

current - Is frequency for dc zero Hz?


We know the frequency of a direct current is zero. The reason is that there is no repetitive pattern.


But I was stumbled when I noticed, why can't that straight line be cut into smaller pieces, and can we treat it as infinite frequency? I have included a picture below as an example



enter image description here


As you can see, with dc, that straight line can be divided into infinitesimal patterns/cycles, since the cycle can be seen as lines repeating over and over again.



Answer



Very clever, but that's not how it works.


By your reasoning you should not only be able to make the frequency infinite, but also 4 Hz, or 100 Hz, or \$\sqrt{2}\$ Hz, all at the same time, with the same signal. And that's why you can't do that: a repeating signal can have only 1 fundamental frequency, which is 1/period.


It would be the same as taking 2 periods of the 4 Hz sine and saying that that's the period, because it also repeats, and then the signal would be 2 Hz. It can't be 2 Hz and 4 Hz at the same time.


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