More Ohm's Law debate

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thingmaker3

Joined May 16, 2005
5,083
Doesn't matter, its the contents that count.
Indeed. I count them to be in error.

Knowing all the resources and databases he has available, it would be right to assume he knows more about things in his purview than you do. Being right with respect to what? Making good decisions, or knowing things?
At least he's not a college professor on a board selecting his own textbook for some dead-end course that teaches fallacies about what is and is not Ohm's Law!

A false correction.
A correction of falsehood.

Where is it coming from?
Where is it coming from?

Check your PMs, if you would be so indulgent.
 

Ratch

Joined Mar 20, 2007
1,070
thingmaker3,

Indeed. I count them to be in error.
Honest answer.

At least he's not a college professor on a board selecting his own textbook for some dead-end course that teaches fallacies about what is and is not Ohm's Law!
I own both books. They both seem to be well written and knowledgeable. I would be careful about pointing out fallacies.

A correction of falsehood.
That is debatable.

Where is it coming from?
From this thread.

Check your PMs, if you would be so indulgent.
Done and answered.

Ratch
 

thingmaker3

Joined May 16, 2005
5,083
thingmaker3,
That's me!

Honest answer.
Honesty is the best policy, neh?

I own both books. They both seem to be well written and knowledgeable.
...with the exception of the Ohm's Law bit...

I would be careful about pointing out fallacies.
You would? Since when?

That is debatable.
Thus, a debate.

From this thread.
From this thread?

Done and answered.
Thank you!

A moniker chosen? Or bestowed by others?
 

Dave

Joined Nov 17, 2003
6,969
I already agreed with the first sentence. I don't understand what you are saying in the rest of the paragraph, especially the part about the "characteristic tangent".
A tangential point on the V-I characteristic (dV/dI) - the characteristic tangent.

Again I say, semiconductors are well known to be nonohmic. That means they do not follow Ohm's law.
The V-I characteristic of certain semiconductors operating in certain conditions are non-ohmic; however at a discrete point on that characteristic (as ΔV and ΔI tend to zero) these devices, like all electronic components, are locally ohmic - that is why I = V/R - Ohms Law - applies in this local region.

Dave
 

Ratch

Joined Mar 20, 2007
1,070
Dave,

The V-I characteristic of certain semiconductors operating in certain conditions are non-ohmic; however at a discrete point on that characteristic (as ΔV and ΔI tend to zero) these devices, like all electronic components, are locally ohmic - that is why I = V/R - Ohms Law - applies in this local region.
I don't agree with the presumption "that is why I = V/R - Ohms Law" is Ohm's law. And I said before, that any material can be considered somewhat linear provided you restrict its range to be small enough. But materials like metals have a much wider range where they are ohmic compared to semi's.

Ratch
 

Dave

Joined Nov 17, 2003
6,969
I don't agree with the presumption "that is why I = V/R - Ohms Law" is Ohm's law.
There is no presumption - this is what Georg Ohm said in his 1827 paper that first proposed Ohms Law. Ohms Law is fundamentally a proportionality relationship that exists between I, V and R and is not a statement of a devices V-I characteristic - if you think differently show me where in Ohms 1827 paper that defines Ohms Law (and the proportionality relationship it describes) does it say to the contrary.

This proportionality relationship may be a function of other variables (for example R may be function of V as is the case with the diode), but it exists at all times - you have stated that in different words here:

Ratch said:
All devices obey the resistance formula V = IR at all times. Not all devices do it in a linear fashion to comply with Ohm's law.
Check the definition of Ohms Law.

And I said before, that any material can be considered somewhat linear provided you restrict its range to be small enough. But materials like metals have a much wider range where they are ohmic compared to semi's.
Correct.

Dave
 

beenthere

Joined Apr 20, 2004
15,819
At this point, there has been a drum roll, and the spotlight is on the stage, where the refutation of V = I/R is about to be performed.

Score stands 1 - 0 for Ohm.
 

jpanhalt

Joined Jan 18, 2008
11,087
This thread has been entertaining. Now that the Olympics is on, perhaps we should all watch women's beach volleyball. At least, I will. :D

John
 

Ratch

Joined Mar 20, 2007
1,070
Dave,

There is no presumption - this is what Georg Ohm said in his 1827 paper that first proposed Ohms Law. Ohms Law is fundamentally a proportionality relationship that exists between I, V and R and is not a statement of a devices V-I characteristic - if you think differently show me where in Ohms 1827 paper that defines Ohms Law (and the proportionality relationship it describes) does it say to the contrary.
Since I don't understand German, I cannot do what you ask. If by proportionality, you mean linear, in that R does not change regardless of I, then yes, I agree with you. But Ohm's law is not the definition of resistance, i.e. R = V/I.

Originally Posted by Ratch
All devices obey the resistance formula V = IR at all times. Not all devices do it in a linear fashion to comply with Ohm's law.

Check the definition of Ohms Law.
I have, I did.
 

Ratch

Joined Mar 20, 2007
1,070
beenthere,

At this point, there has been a drum roll, and the spotlight is on the stage, where the refutation of V = I/R is about to be performed.
Neither Ohm's law or V=IR has been or will be refuted.

Ratch
 

Dave

Joined Nov 17, 2003
6,969
Since I don't understand German, I cannot do what you ask. If by proportionality, you mean linear, in that R does not change regardless of I, then yes, I agree with you. But Ohm's law is not the definition of resistance, i.e. R = V/I.
Ohms Law explicitly defines the proportionality relationship I = V/R - this is what Ohms 1827 paper on Ohms Law says.

Dave
 

Ratch

Joined Mar 20, 2007
1,070
Dave,

Ohms Law explicitly defines the proportionality relationship I = V/R - this is what Ohms 1827 paper on Ohms Law says.
Yes, and I = V/R is used to illustrate the proportionality. That is what Ohm's law is about. Not all materials follow Ohm's law and so are not ohmic. When used to calculate the resistance, V = IR is not Ohm's law anymore. In other words, to say that two things are proportional to each other does not mean that the proportion necessarily defines the proportionality constant all values. So when we apply V=IR to a semiconductor, we loose the constant proportionality, and consider the semiconductor to be nonohmic even though V = IR is correct. The following link illustrates what I mean. Notice the paragraph toward the end which begins "The law is strictly true only for resistors whose resistance does not depend on the applied voltage..."

Ratch

http://www.juliantrubin.com/bigten/ohmlawexperiments.html
 

Dave

Joined Nov 17, 2003
6,969
Yes, and I = V/R is used to illustrate the proportionality. That is what Ohm's law is about. Not all materials follow Ohm's law and so are not ohmic. When used to calculate the resistance, V = IR is not Ohm's law anymore. In other words, to say that two things are proportional to each other does not mean that the proportion necessarily defines the proportionality constant all values. So when we apply V=IR to a semiconductor, we loose the constant proportionality, and consider the semiconductor to be nonohmic even though V = IR is correct. The following link illustrates what I mean. Notice the paragraph toward the end which begins "The law is strictly true only for resistors whose resistance does not depend on the applied voltage..."
Ohm defined a proportionality relationship between V, I, and R through experimental work on conductors. This proportionality relationship may or may not exist across the whole device characteristic (ohmic or non-ohmic) but as we agree applies always and may be a function of other variables - something your article concurs with. Ohm concluded that most materials appear to obey the proportionality relationship across its characteristic (intuitively given the relative maturity - or lack of - of this field at the time he published this work), but that isn't what Ohms Law is. Fundamentally, Ohms Law is a statement of the proportionality relationship, it is not a statement of a devices characteristic behaviour.

This is going round in circles. I suggest you learn German and read Ohm's papers to see what he actually said. At this point in time, this thread is going nowhere.

Dave
 
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