"Chuck Harris" wrote in message
...
Ratch,
It comes down to a basic ability to read and understand
algebra!
If I tell you that y = m*x + b, and I tell you the variables
are x and y, do I really have to tell you that m and b are
constants?
If they are not constants, then I have to show that they are
dependent on x (or y). To do that I would write them as:
y = m(x) * x + b(x) Which changes the character of the
equation tremendously.
L&M told you that most, but not all materials have a current
density that is proportional to the electric field. Then,
they gave you the equation:
j = (1/rho) * E (9-16)
[not:
j = (1/rho(E)) * E or j = (1/rho(j)) * E ]
and told you it (9-16) was Ohm's Law.
Really, though, whether or not R is ohmic, is immaterial,
as long as you can describe R, the relationship we all
call Ohm's law works... it has to, because R is defined
to make it work.
I think you are refering to the "relationship" as being the equation.
That is not Ohm's law, the linearity property is.
If you want to argue this further, you really must cite
Georg S. Ohm's research work that shows he was only
interested in being deified over materials that are
purely ohmic, and you really must cite the individual, or
group that first coined the phrase "Ohm's Law" to see what
they meant by it.
And how does anyone do that? How would I track something like that
down and interview folks that have been dead for such a long time? One can
assume that it is called Ohm's law because he was the one that proposed that
current is proportional to voltage for many materials.
Citing Resnick, or L&M, or the tooth fairy
doesn't do it. None of them were involved in the deification
process, and as a result their arguments are pure speculation,
or conjecture.
I hope you mean giving credit where credit is due as being the
"deification process" Resnick and L&M are experts in their field, and their
opinions should be taken into account and evaluated. You can argue that
they did not explain things well enough, or are mistaken, or even careless.
But you cannot realistically say their writtings on this subject are
imaginary, like the tooth fairy.
The overwhelming body of evidence in the engineering literature
of the last 100+ years suggests that E = iR is properly named
as Ohm's law, just as most of us think it is.
I think the overwhelming evidence is that resistance formula has been
wrongly named for a long time now. Ratch
-Chuck
Ratch wrote:
"Chuck Harris" wrote in message
Eq. (9-16) describes the current density in terms of the electric
field at a point in a conductor (Fig. 9-11). It is called Ohm's law.
materials that obey Ohm's law are usually called ohmic conductors. This
relation enables us to calculate the current flowing through a wire of
length L which is connected to two terminals - points between which
there is a potential difference V....]
Now here is where they crash. They first give equation (9-16) and
call
it Ohm's law. Then they say that all materials that obey equation
(9-16)
are ohmic. Well, all materials obey the resistivity equation (9-16).
Therefore by their reasoning, all materials are ohmic. They go on to
say
that Ohm's law can be used to show the relationship between
resisitivity,
current density, and electric field. That is certainly true for
Equation
(9-16), but that is the resistivity equation and it stands on it own
independent of Ohm's law. The resistivity (9-16) is used to determine
whether a material has the Ohm's law property, but it is not Ohm's law
per
se.
L&M could have said a bit more about what they meant about a material
not following Ohm's law; how they meant that a material that has a non
constant rho is non ohmic. However, I caught the meaning the first time
I read it, so it cannot have been too badly worded.
You were primed to understand it because of your exposure to this
discussion.
The trip from (9-16) to: V = RI is just a straight forward
rearrangement, and substitution. It still states the same thing as
(9-16). A material is non ohmic if R is not a constant.
I don't see L&M saying anything that corresponds to the last
sentence
above. Again, the resistance equation V=IR can be used to determine if a
material has the Ohm's law property, but V=IR stands on its own and is
not
Ohm's law per se. Look at
http://maxwell.byu.edu/~spencerr/websumm122/node50.html again. Ratch