|Re: HP-41 Ohm's Law Program|
Message #13 Posted by Les Bell on 28 Dec 2010, 7:07 p.m.,
in response to message #12 by Walter B
As a member of the IEEE, I have to defer to my ancient copy of the "Electronic Engineer's Handbook", Donald G. Fink (ed), McGraw-Hill, 1975. Para 1.27 states:
Electrostatic Potential and Potential Difference.
[...] While it is not possible to specify uniquely the absolute potential of any point in an electric field, the difference in potential between two points in the field can be determined when the manner in which the electric field strength varies between the points is known.
The potential difference between two points a and b in an electric field of strength E is, then
Vab = . . .
I've omitted the rest of the equation - I wish the web and email spoke LaTeX, but it doesn't. ;) And for the rest of this 2.8"-thick (oops: 71mm-thick) book, so it goes - consistently using V to represent voltages (which we all know are potential differences). The word "tension" doesn't appear in the index, and disappeared from electrical English usage around the same time as vacuum tubes.
Now, to business:
French even inform you (just for the case case you didn't know before) this U is the "standardized symbol" for electrical tension - please check the site of IEC - regards to Les ;)
Ah, yes - but if you look one line higher(http://www.iec.ch/zone/si/si_elecmag.htm#si_epo), you'll see:
Electric potential, V
Since you can't measure an absolute potential, there is no unit for it, and the SI unit, the volt, must represent a potential difference. So V and U are the same thing by different names, and the IEC should stick to what it's good at: setting standards for power supply connectors. ;)
Please don't confuse "international" with "English speaking country" or "former British colony".
We had French and (it's been so long I can't remember) either Dutch or German editions as well - and in my occasional communications with them I can't recall "U" being used. I certainly never received any requests to explain our use of "V", but I would certainly have been puzzled if I had seen "U = IR" in the copies of their editions that I occasionally browsed.
My advice is, in any calculator program which has to represent voltage and which you hope will be used internationally, stay away from "U". We all know what "V" is, even if we resent its imperialistic connotations. And for proof that "U" is confusing, just read this thread and those linked from it.
Of course, the prudent programmer will probably wish to determine the Mandarin/Chinese/Japanese character for voltage, since it will probably ultimately trump "V", "E" and "U". But since it probably isn't on the keyboard of the HP-41 (and since they probably use "V" anyway ;) ) I'd say you're safe for the time being. And besides, Alessandro Volta deserves the credit.
With tongue planted firmly in cheek,