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Topic: Ohm's Law (Read 2 times) previous topic - next topic


Hey, I remember when Hertz was what it did after your took an inside pitch to the head. It was Cycles Per Second, up until the 70's. ;)

Evidently there was a lot of resistance to changing from CPS to Hz. I remember a tongue-in-cheek article in QST magazine about how to convert cycles-per-second to Hertz, complete with nomographs.

My US college text books in the early 80's used V=IR, and that's what I've used ever since.


I can't find an explanation of why I for current tho.  Like many things, it was defined well before my time 8)
I was told that "i" was already used for "imaginary" number in mathematics and since that comes into play in AC circuits another symbol was chosen.  The wiki thing sounds reasonable too.  Who knows? 

EEs use "j" for the square root of -1 instead of "i" to avoid confusion with current.

Except that i, j & k are the imaginary part of vectors and match up with X, Y & Z, a vector was commonly written as (X + i, Y + j, Z + k).

So you have to be careful how you use them as you might just be sending some other message. Like trying to speak English with an English man, and Irish man, and American, an Aussie & an Kiwi. Lots of talk but little comprehension...


Well as a measure of the rate of change of frequency, Hz / sec would make sense  8), just like m/s2 for linear acceleration.
Well, as you age, hurts per second makes perfect sense.


What do you know... I'm absent for a day and entire page of answers greets me. :)
Interesting to hear others having come across different notation, too.

I don't know why this region decided to use U; it probably comes from notation for potential energy (which, by the way, I was always thought to be Ep and nothing else).
In any case, it strikes me as beneficial not to use same letter for physical quantity and the unit of that physical quantity.



In "Elements of Programming Style", Kernighan and Plauger point out many example programs (from textbooks!) that confuse E and V and get the values wrong accordingly.


I would sooner attribute that to the lack of properly established standard, than to usage of any particular letter.

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