Re: Ohm's Laws
- From: Hatunen <hatunen@xxxxxxx>
- Date: Mon, 05 Nov 2007 21:55:30 -0700
On Mon, 05 Nov 2007 18:01:15 -0800, Bob Cunningham
<exw6sxq@xxxxxxxxxxxxx> wrote:
A discussion in another thread made me curious to see how
the _New Shorter Oxford English Dictionary_ (_NSOED_)
defines Ohm's law. On pursing this curiosity, I found that
they have an error in their definition of the Ohm's law that
many people, but evidently not Mr or Ms Lodder, know about.
But the more startling finding was that there is yet another
Ohm's law, one having to do with the decomposition of a
complex sound into its component sounds.
First the error: They state that one of Ohm's laws says
[...] that the potential difference between any
two points of [a circuit] is proportional to the
resistance between them;
Only under special circumstances is it true that the
potential difference between any two points of a circuit is
proportional to the resistance between them. The potential
difference depends upon the amount of current flowing
between the two points, which in turn depends upon the total
resistance in series with the source. Their assertion is
easy to disprove by means of a counterexample: Let the
resistance between the two points be ten ohms. if the
circuit contains in series with the ten ohms another
resistance of ten ohms, then doubling the first ten-ohm
resistance will not double the voltage across it. it will,
instead, increase the voltage by 50 percent.
The definition is badly worded but can be taken to mean
"proportional to the rsistance between them with respect to the
ccircuit as a whole." In your example with the two ten ohm
resisters you have added resistance to the circuit by doubling
one of the resisters, which alters the circuit and the problem.
Instead, consider that potential across one of the ten ohm
resisters is E volts, then the potential across both ten ohm
resisters, or twenty ohms, will be 2E volts. In other words, the
potential is, indeed, proportional to the resistance.
This is, of course, simply a consequence of the current being the
same throughout the circuit and applying E=IR, the Ohm's Law we
learn first. Ohm's Laws e=ir and e=iz come later.
The second Ohm's law is, according to _NSOED_
(b) that a complex musical sound is heard as the sum
of a number of distinct pure tones which can be
resolved by Fourier analysis. M19.
That principle was central to some of my work during my
working years, but I had never heard it attributed to Ohm.
New to me, too.
--
************* DAVE HATUNEN (hatunen@xxxxxxx) *************
* Tucson Arizona, out where the cacti grow *
* My typos & mispellings are intentional copyright traps *
.
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