ohm's law clarification

[Roff]

This is much ado about nothing, as far as I'm concerned.
I never had a problem with Ohm's law before this thread.
I still don't.

 

[DerStrom8]

This is much ado about nothing, as far as I'm concerned.
I never had a problem with Ohm's law before this thread.
I still don't.

Hehe. Same here

I know that the formula itself isn't ohm's law. It only describes it--it shows what the law states. That's how I look at it.

 

[Sceadwian]

I know that the formula itself isn't ohm's law. It only describes it--it shows what the law states. That's how I look at it.

The problem is that's not how it's taught and that is most definitely not how most people think of it.

 

[DerStrom8]

The problem is that's not how it's taught and that is most definitely not how most people think of it.

But how is that a problem? The formula is a representation of the idea which is ohm's law. I don't see how it's different from any other name or word. They are all representations of the actual idea.

By the way, Eric was kind enough to move the discussion that didn't belong here to another thread, so let's try to keep this strictly on Ohm's law now. I know you weren't trying to change it. I'm just saying that for future posts

 

[Sceadwian]

The formula is a representation of the idea which is ohm's law.

No it's not. The paper attributed to being the source of Ohm's Law was a physical experiement, it's been distorted ad infinitum throughout the years in it's meaning and teaching refrence, there is no clear definition of specifically what Ohm's law even is anywhere every source I find shows a slightly different viewpoint on it. Ohm's Law does not even actually apply to any known material in physics outside of the very carefully controlled experiments he produced and even then the results weren't perfectly linear.

The various equations have become very useful in electronics for simplified systems or systems within a boundary but the law itself doesn't actually make any sense for real world materials nor does it have any relation of any kind whatsoever to semi conductors,there's so much more math that has to be added to make things work in the real world it's ridiculous. This confusion is linguistic only! The reason it's still called Ohm's law is for the simple reason that there's nothing else to call it and it's so widley in use there would be a backlash if the scientific community tried to redefine the equations under some other name.

In electronics the equations are used because they work fantastically well, Ohm didn't create them he was just the first to publish a paper that described something linkable to what we now use, and the only reason he did the experiments in the first place is because he was getting poor wages as a teacher and at the time the only way to get a bigger pay check was to publish papers.

I do still need to research what Cavendish wrote in more detail and see how it directly applies to what is shown in Ohm's Paper.

 

[DerStrom8]

No it's not. The paper attributed to being the source of Ohm's Law was a physical experiement, it's been distorted ad infinitum throughout the years in it's meaning and teaching refrence, there is no clear definition of specifically what Ohm's law even is anywhere every source I find shows a slightly different viewpoint on it. Ohm's Law does not even actually apply to any known material in physics outside of the very carefully controlled experiments he produced and even then the results weren't perfectly linear.

The various equations have become very useful in electronics for simplified systems or systems within a boundary but the law itself doesn't actually make any sense for real world materials nor does it have any relation of any kind whatsoever to semi conductors,there's so much more math that has to be added to make things work in the real world it's ridiculous. This confusion is linguistic only! The reason it's still called Ohm's law is for the simple reason that there's nothing else to call it and it's so widley in use there would be a backlash if the scientific community tried to redefine the equations under some other name.

In electronics the equations are used because they work fantastically well, Ohm didn't create them he was just the first to publish a paper that described something linkable to what we now use, and the only reason he did the experiments in the first place is because he was getting poor wages as a teacher and at the time the only way to get a bigger pay check was to publish papers.

I do still need to research what Cavendish wrote in more detail and see how it directly applies to what is shown in Ohm's Paper.

Hmm, very interesting. Do you have sources to back up these claims? I'd definitely be interested in reading them. I've been wrong more than once. This is just what I've grown up with--that Ohm's Law describes the relationship between V, I, and R, in a perfect-world setup. You're saying this is incorrect? I'm really not sure about that, personally, but I'm open to proof that verifies that.

 

[Sceadwian]

Just look up the biographies of Ohm that are available via searching as far as his personal life goes.

As far as to the document itself that Ohm became famous for (which I've attached) read for yourself. Please note that the equation which most directly referenced in it that is related to what we know as Ohm's Law is only true under the specific set of conditions that he observed his results under, the math can not be extrapolated outside of the conditionals which created it, any likeness to extrapolations of that equation outside of his experimental tests aren't his to be accredited.

Keep well in mind his only other contribution to science was Ohm's acoustic law, which is known to be as false as Ohm's first law is if you look at it a little closer.

 

[DerStrom8]

Please note that the equation which most directly referenced in it that is related to what we know as Ohm's Law is only true under the specific set of conditions that he observed his results under, the math can not be extrapolated outside of the conditionals which created it, any likeness to extrapolations of that equation outside of his experimental tests aren't his to be accredited.

Absolutely. I can't argue with that. Usually when "Ohm's Law" (I mean the formula) is used, it simulates a perfect-world situation with basic circuits and perfect components.

To the OP: If someone refers to "Ohm's Law", it is probably safe to assume they mean the relationship between voltage, current, and resistance/impedance. Don't get hung up on this behind-the-scenes information, since it does not have much to do with our ideas of the law today. It is good to know the history, as this thread seems to have dug up, but do not dwell on it much. It is not here to confuse you. If you ask me, you can believe that Ohm's Law is the relationship between the electrical characteristics and get along fine, but keep this thread in the back of your mind. Obviously, meanings have changed, so it's your choice.

Regards

 

[Sceadwian]

To the OP: If someone refers to "Ohm's Law", it is probably safe to assume they mean the relationship between voltage, current, and resistance/impedance.

I second that, I get hung up on the semantics, but it's a very simple thing for me to fix, I just try not to use the term myself and refer to it as voltage/current/resistance equation, you're generally trying to solve for one so you just call it the other two based on the situation.

Other people are of course entitled to disagree with me but there are clearly no facts that support absolutely a true hard reliable definition of what Ohm's Law is, so it's bound to cause discord. I have downloaded Maxwells publication of select notes he garnered from Cavendish, the problem I have right now is that it's 500 pages of text that aren't searchable because they're scans and between the font and the writing style of the time it's difficult to skim like modern technical writing. I'll plod through it to see if there's anything substantive in it to show Cavendish understood the relationship first. I've found many claims that this is so but no references as to why! Only references that it was experiments he did with layden jars.

I believe the most detailed description I found of what Cavendish toyed with which I unfortunately can't reference because it was a random website I came across stated very different equations but the heart of it was equivalent to what has been called Ohm's law.

If I come across something enough to add I will, as it is I think the conversation has pretty well puttered out, and there's no point in taking apart every word every person posts about for faults.

 

[KeepItSimpleStupid]

hey:

Resistivity is a material property (units of ohm-cm). It is likely temperature dependent and may have other dependencies.

Resistance is not a material property. It depends where you measure it and how much material is between the probes etc.