In article nHFSa.95145$OZ2.20552@rwcrnsc54,
mentioned...
"Chuck Harris" wrote in message
...
Hi Ratch,
Ratch wrote:
Wait a minute, if L&M say that Ohm's law is V=IR (which it is not),
and
materials that obey Ohm's law are "ohmic", then by L&M's definition, all
materials are ohmic because the resistance formula V=IR is always
correct
for all materials. How is a material defined as "nonohmic"? Ratch
No, not quite, ohmic materials by definition have a current density that
is *proportional* to the electric field. Or in other words have a rho
that is a simple constant.
j = E/rho, or E = j * rho
If you have a material where rho is not a simple constant, but rather is
a function of current density, you have a non-ohmic material.
I agree with what you said above.
This applies to either way of writing Ohm's law, because rho and R are
proportional to each other.
Yes, rho and R are proportional to each other, but that does not answer
the question I asked before (see the first paragraph above). How does L&M
define something as nonohmic when according to what they say, everything is
ohmic because it follows V=IR (which they say is Ohm's law).
So, as a result, if R is some function of I, the material is non ohmic.
I agree with that, but according to what you said about what L&M
writes, that never happens because all materials follow V=IR. Does L&M
mention
nonohmic materials? Ohm's law cannot be both V=IR and constant resistance
as current varies. Which one does L&M say it is? Ratch
There is no inconsistency.
Yes, according to what L&M says there is. Ratch
I think one has to look at the history of this. When Ohm's law was
defined, it's possible that non-ohmic conductors had not been
discovered. Hence everything that conducted obeyed Ohm's Law.
In that context, V=I*R would always apply. Hence at that time, it was
considered a part of Ohm's Law.
But later, things changed...
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