ohm's law clarification

[Sceadwian]

I believe Ohm discovered the law of electrical linearity, which states that some materials have electrical current linearity and others don't.

The problem with that statement is that it is now currently known in physics that the systems that he used in his experimentation are not actually linear the equation is false, we have the instrumentation and methods available today to prove that Ohm's Law in fact doesn't hold a shred of relation to reality if you look close enough, then again this goes for a lot of laws like most of what Newton did. Granted Newton obviously contributed Ohm wasn't the first to make this proportional relation.

MrAl, I think that it's safe to say that Ohm's true contribution to science weren't all that great, his only other noted 'law' was proven false, and Ohm's law itself is now known on a fine enough level to not be true outside of course systems. Cavendish did make the relation first, this is easily found by reading Maxwells publication of Cavendish's notes, I've also read Ohm's actual publication (the translation at least the original is in German though I have that one too I can't read it )

I would like to point out that the equations that are given as being Ohm's law are not in fact found in his original publication, the image bellow is what he ACTUALLY published, please feel free to read his original publication for verification it's in the public domain.

It's difficult to delve too deeply into the true intention of what occurred to give Ohm the credit which I don't find unfounded mainly due to there being little verifiable evidence outside of the published works that can't be shown to be hearsay. Something I'll try to look into in my spare time, which is little, I've used too much time here today already spring here was early, it's nearly a summers day and the yard work to be done is huge.

I do however find Ohm's exalted status to be undeserved for what he discovered is nothing more than what the first man that realized that an object that was round will roll and that it is important. It's not that he's an idiot, but moreso that he was just the first guy that this simple equation could be attributed to based on who knew what at the time.

I'm sure lost in the clouds of time the core of this equation was being steeped in the minds of curious persons long before those whom are noted for mentioning it on paper for history to record 'discovered' it. What he showed is important but it did not come from his mind, it came from simple observation, someone else some other time would have noticed it (and did)

 

[Ratchit]

Sceadwian,

The problem with that statement is that it is now currently known in physics that the systems that he used in his experimentation are not actually linear the equation is false, we have the instrumentation and methods available today to prove that Ohm's Law in fact doesn't hold a shred of relation to reality if you look close enough, then again this goes for a lot of laws like most of what Newton did. Granted Newton obviously contributed Ohm wasn't the first to make this proportional relation.

Ohm gets credit for working with resistive materials, and noticing that some materials like metals have a wide range where the voltage used to measure the resistance is irrelevant. That applies to most solid and liquid metals. He may have not had the precise instrumentation we have today, but he still noted the linearity. During his work, Ohm must have been familiar with the definiton of resistance (R=V/I), but for some reason today, too many people today think that definition is Ohm's law. It isn't.

Ratch

 

[meowth08]

"Ohm's law" refers to that law of electricity, that V=IR, I=V/R, R=V/I, etc. It would help you to look at the big picture, rather than at each individual little piece of it, Ratch.

I don't want this to get into another big long argument like it did last time without the OP's permission. Before I reply again, I'm going to ask--meowth08, is this the type discussion you were looking for?

Hi D8,

You asked me if this is the type of discussion I was looking for. Actually, I am going with the flow. I know you people are good enough to know how the discussions should go. I am thankful to you for remembering me as the maker of this thread and asking for my opinion. I also hope that everybody would remember the intentions of the thread- clarification!

I know that there are already some arguments on the previous posts and I find them interesting. Arguments are good as long as they are presented in a polite manner. I just hope that these would lead to a point where the intention of the thread is met and not to throwing s***s to each other.

Just want to share...

I remembered what I read on a newspaper long time ago written by Atty. Adel Tamano about his experience when he went to Singapore to watch a hearing. He had seen how Singaporean lawyers treat each other inside the court. They address their colleagues as their learned friend and speaks politely about their arguments. After reading that, my belief changed. I thought before that those lawyers who shout inside the courts are the real lawyers. They are fearless. But no! What a real lawyer is he who presents his arguments in a polite and respectful manner. And the real purpose of presenting arguments is to bring out the truth.

MrAl,

Do you still remember the title of the book you had before. The semester just ended and I'm away from school right now. I can't go to the library and search for books. What I am thinking is, maybe, there is an e-book same as that one you had.

D8,

I forgot to say something. You were talking that V=IR, I=V/R, R=V/I as ohm's law. Well, it contradicts to what I have learned from the first three replies. Can you clarify this for me?

Ratch,

Your posts are the same to that of the previous thread. You are very consistent on what you believe. The word in bold indicates that I'm a little bit confused now. If only there is no contradiction to your posts, I would say you're stating a fact.

 

[DerStrom8]

Hi D8,

You asked me if this is the type of discussion I was looking for. Actually, I am going with the flow. I know you people are good enough to know how the discussions should go. I am thankful to you for remembering me as the maker of this thread and asking for my opinion. I also hope that everybody would remember the intentions of the thread- clarification!

I know that there are already some arguments on the previous posts and I find them interesting. Arguments are good as long as they are presented in a polite manner. I just hope that these would lead to a point where the intention of the thread is met and not to throwing s***s to each other.D8,

I forgot to say something. You were talking that V=IR, I=V/R, R=V/I as ohm's law. Well, it contradicts to what I have learned from the first three replies. Can you clarify this for me?

Thanks meowth08. "Ohm's Law" refers to the overall relationship between voltage, current, and resistance. The formula(s) are used to describe the relationship. It allows people to calculate one from the other two, because of Ohm's Law. It is safe to say that V=IR is Ohm's law, since it is the relationship which Ohm's law describes. The law describes the relationship, as do the formulas. Therefore, the law and the formulas are, for all intents and purposes, the same.

 

[DerStrom8]

DerStrom8,
Not so. For instance, speed = distance/time is a definition of speed. You have never heard of it called the "speed law", have you? A definition and a law are two entirely different things.

You can call it the "speed law". It would mean the same thing. As I've said so many times before, it is not the name that counts. It's the thoughts, ideas, and purposes that go with it. It is a law in physics that speed is distance over time. It's an ideal law--one that cannot be broken.

Not only do they work differently, the results are different. Resistance takes electrical energy out of a electrical circuit, while reactance stores energy, redirects it, and gives it back. Ohm's law is not used to calculate circuit values. The definition of impedance is used instead (Z=V/I).

Z=V/I looks an awful lot like R=V/I, now, doesn't it? It is the EXACT SAME RELATIONSHIP! Therefore, it makes complete sense that the same unit would be used for impedance, reactance, and resistance. In math, it all works the same way.

That is the crux of the matter. You keep insisting that V=IR and its variants are Ohm's law. I and two good physics books I referenced in post #4 of this thread state otherwise. No matter how big the picture is, we have to get past that fact.

See my previous post regarding the difference between the law and the formulas. I'm not sure how much more simple it can get.


meowth08, thanks for letting me reply to that. It's something that I felt was very important to clarify that what Ratch is saying is NOT necessarily true. You'd need to dig deeper into the understanding of how everything works--how voltage relates to current and resistance, and what ideas were actually given the name "Ohm's Law". With no disrespect to ratch intended, he is only scratching the surface and not thinking about the entire picture.

Regards

 

[Ratchit]

meowth08,

Your posts are the same to that of the previous thread. You are very consistent on what you believe. The word in bold indicates that I'm a little bit confused now. If only there is no contradiction to your posts, I would say you're stating a fact. .

Well, others do contradict what I state, so you are going to have to sort out what is fact and what is chaff. The way to do it is to list what you know is correct and see how that and any other information ties in and makes sense. So let's summarize. I state that V=IR and its variants are a definition of resistance, not Ohm's law. My believe is supported by direct quotes from two good physics books written by three physics professors that I listed in post #4. I even threw in a website that agrees with me. Why is it that no one seems to contradict those references? If they don't believe the above, then they should show something that puts those two references in doubt. If V=IR is not a definition of resistance, they pray tell me what is? Do you think it is possible that Ohm started his work without knowing what resistance was, that is, V=IR? Do you think he would be famous for restating a definition? At least one person in this forum believes that a definition and a law are the same thing. Now a dictionary contains thousands of word definitions. Would you call a dictionary a lawbook? Voltage is defined by energy/charge, so would you call it the "voltage law"? That is the type of reasoning you have to make in order to decide in your own mind who is correct. Ask away if you have any questions.

Ratch

 

[DerStrom8]

Well, others do contradict what I state, so you are going to have to sort out what is fact and what is chaff. The way to do it is to list what you know is correct and see how that and any other information ties in and makes sense. So let's summarize. I state that V=IR and its variants are a definition of resistance, not Ohm's law. My believe is supported by direct quotes from two good physics books written by three physics professors that I listed in post #4. I even threw in a website that agrees with me. Why is it that no one seems to contradict those references? If they don't believe the above, then they should show something that puts those two references in doubt. If V=IR is not a definition of resistance, they pray tell me what is? Do you think it is possible that Ohm started his work without knowing what resistance was, that is, V=IR? Do you think he would be famous for restating a definition? At least one person in this forum believes that a definition and a law are the same thing. Now a dictionary contains thousands of word definitions. Would you call a dictionary a lawbook? Voltage is defined by energy/charge, so would you call it the "voltage law"? That is the type of reasoning you have to make in order to decide in your own mind who is correct. Ask away if you have any questions.

Ratch

Ratch, one website and names of three textbooks which (most likely) none of us have are not really legitimate sources that you can use against other members here. Without those books, we can't prove that you're correct, and you can't say that we are all wrong because we don't argue with them.
You can also stop with the definition vs. law thing. A definition is a law. Yes, a dictionary could be considered a type of lawbook, but as usual, you're just fighting over names and titles. Instead of talking about what things could be called, why don't you start thinking about the ideas behind them that are important. You're fighting over names rather than the actual material. What you're doing right now is like reading the cover of a book and then saying that you now know everything that is written inside. You just can't do that.

 

[Ratchit]

DerStrom8,

You can call it the "speed law". It would mean the same thing. As I've said so many times before, it is not the name that counts. It's the thoughts, ideas, and purposes that go with it. It is a law in physics that speed is distance over time. It's an ideal law--one that cannot be broken.

No, because calling it a law when it is a definition obfuscates the thoughts, ideas, and purposes that the meaning is supposed to convey.

Z=V/I looks an awful lot like R=V/I, now, doesn't it? It is the EXACT SAME RELATIONSHIP! Therefore, it makes complete sense that the same unit would be used for impedance, reactance, and resistance. In math, it all works the same way.

You are preaching to the choir on whether ZXR should all have units of ohms. I fully agree. I am stating. however, that they produce vastly different results in a circuit.

See my previous post regarding the difference between the law and the formulas. I'm not sure how much more simple it can get.

It is not that I don't understand what you are saying. I just don't agree with it. That is something you should work on. Specifically, what is the definition of resistance, and how is a definition also a law.

Ratch

 

[DerStrom8]

No, because calling it a law when it is a definition obfuscates the thoughts, ideas, and purposes that the meaning is supposed to convey.
It is not that I don't understand what you are saying. I just don't agree with it. That is something you should work on. Specifically, what is the definition of resistance, and how is a definition also a law.
Ratch

If something is a definition, it means it's absolute. It's always going to be true, and nothing can change that. An ideal law is something that is always true, that can't be changed. It is a rule that cannot be broken. If V=IR is a definition for voltage, then it is also true to say that it's a rule. Voltage does, in fact, equal current times resistance. That is a rule that cannot be broken--it will always be true. A rule that cannot be broken is a law. If you look up the "definition" of "law" in a dictionary, you should be able to see what I mean.

 

[Ratchit]

DerStrom8,

If something is a definition, it means it's absolute. It's always going to be true, and nothing can change that.

Yes, it will be true, unless the definition changes.

An ideal law is something that is always true, that can't be changed.

Not so. The Ideal Gas Law is modified when the circumstances are not ideal. An ideal law does not mean it cannot be broken.

If V=IR is a definition for voltage, then it is also true to say that it's a rule.

A definition is not a rule. Defining something does not make it a rule.

Voltage does, in fact, equal current times resistance. That is a rule that cannot be broken--it will always be true.

That is its relationship with current and resistance. Have you heard of the "voltage law"? Just because something is always true, does not make it a "law".

If you look up the "definition" of "law" in a dictionary, you should be able to see what I mean. .

Twenty-seven different definitions. Probably the one you are interested in is "a principle based on the predictable consequences of an act, condition, etc." If I hit my thumb with a hammer, is that the Law of Hurt?

Ratch

 

[DerStrom8]

DerStrom8,
Yes, it will be true, unless the definition changes.

An actual law WILL NOT change. If it is a real law, it will always be true. Sure, sometimes things are called laws when in reality we don't know everything about it, so only our understanding changes. But if something is truly a law, then the definition will never change. Can I make myself any clearer?

Not so. The Ideal Gas Law is modified when the circumstances are not ideal. An ideal law does not mean it cannot be broken.

I'm not talking about an "ideal law". I'm talking about an ideal "law". Ideally, a true law won't change--it'll always be true and always stay the same. As will the definition.

A definition is not a rule. Defining something does not make it a rule.

If something is defined, rules are created about it. That's just how things work. If I define X as Y+2, then X will always be Y+2. It is a rule that I created by defining it. Rules and laws are not any different.

That is its relationship with current and resistance. Have you heard of the "voltage law"? Just because something is always true, does not make it a "law".

Here you go with the name stuff again. And yes, if something is always true, it is a rule that it will always be true. And a rule is a law. Try thinking outside of the box, Ratch. Don't only look at what's inside. You'll get much further if you do.

Twenty-seven different definitions. Probably the one you are interested in is "a principle based on the predictable consequences of an act, condition, etc." If I hit my thumb with a hammer, is that the Law of Hurt?

Call it what you want. I could call it the law of fried chicken, and it'd be true as long as other people knew what I was talking about. If you hit your thumb with a hammer, it will hurt (as long as you have nerves), so sure, you could call it the "Law of Hurt".


I feel we're going off topic again. Let's try to steer this back to the OP's question.

 

[Ratchit]

DerStrom8,

Ratch, one website and names of three textbooks which (most likely) none of us have are not really legitimate sources that you can use against other members here. Without those books, we can't prove that you're correct, and you can't say that we are all wrong because we don't argue with them.

Actually it was 2 books, 3 professors, and 1 website. I did not just reference those books, I quoted from them. You can evaluate those quotes, and if you don't, then I have good reason to believe your arguments do not stand. Anyway I photocopied the important section from Haliday and Resnick put it in this post as an attachment. Notice that page 780 says "We stress that V=IR is not a statement of Ohm's law." and "The relationship of R=V/I remains as the general definition of the resistance of a conductor whether or not the conductor obeys Ohm's law". I apologize for the last page being upside down.

You can also stop with the definition vs. law thing. A definition is a law.

I don't believe it.

Yes, a dictionary could be considered a type of lawbook, but as usual, you're just fighting over names and titles.

If I walk into a library, people will laugh and point at me if I asked for dictionary lawbook. They will probably show me a dictionary of law terms.

Instead of talking about what things could be called, why don't you start thinking about the ideas behind them that are important.

I know about the ideas behind them. Just like I do when NASA "walks" in space.

You're fighting over names rather than the actual material.

There is nothing wrong in naming something correctly. It reduces confusion.

What you're doing right now is like reading the cover of a book and then saying that you now know everything that is written inside. You just can't do that.

And I haven't. I read the inside of the book, too. Trust me, I have.

Ratch

 

[DerStrom8]

DerStrom8,
Actually it was 2 books, 3 professors, and 1 website. I did not just reference those books, I quoted from them. You can evaluate those quotes, and if you don't, then I have good reason to believe your arguments do not stand. Anyway I photocopied the important section from Haliday and Resnick put it in this post as an attachment. Notice that page 780 says "We stress that V=IR is not a statement of Ohm's law." and "The relationship of R=V/I remains as the general definition of the resistance of a conductor whether or not the conductor obeys Ohm's law". I apologize for the last page being upside down.

I don't believe it.

If I walk into a library, people will laugh and point at me if I asked for dictionary lawbook. They will probably show me a dictionary of law terms.

I know about the ideas behind them. Just like I do when NASA "walks" in space.

There is nothing wrong in naming something correctly. It reduces confusion.

And I haven't. I read the inside of the book, too. Trust me, I have.

Ratch

Those texts do not go against what I was saying. In fact, if you read them more carefully, and perhaps re-read my posts, you'll see that they're actually agreeing. I'm just taking it one step further to connect it to the OP's question, so that it is easier to understand. If you don't see that, then it's pointless for me to continue here. I'm done arguing. It's clear you aren't getting my point, and if you haven't by now, I think it's obvious you never will. You are not "reading the inside of the book", so to speak. If you were, you'd have seen my point long ago. I'll let you have the last word, since that seems like what you're really interested in. Right now, this argument is just wasting space, so I'm finished.

meowth08, sorry for being part of this mess and cluttering up your thread. I hope you can find someone who actually understands entirely what ohm's law is to explain it to you.

Kind regards,
Der Strom

 

[Ratchit]

DerStrom8,

Those texts do not go against what I was saying. In fact, if you read them more carefully, and perhaps re-read my posts, you'll see that they're actually agreeing

Well, that text says that V=IR is not a statement of Ohm's law, while you seem to believe it is. Furthermore, it says that R=V/I is the definition of resistance, whether or not the conductor obeys Ohm's law. You seem to say that a definition is the same as a law. You are right in that I cannot square what you say with what the text states.

meowth08,

Well, there you have it. We both made our best arguments, and it is up to you to decide what to believe. Happy choosing.

Ratch

 

[Roff]

I will probably regret getting involved in this thread, but here goes:

I find these definitions of scientific law on several **broken link removed**:

LAW

1) An empirical generalization; a statement of a biological principle that appears to be without exception at the time it is made, and has become consolidated by repeated successful testing; rule (Lincoln et al., 1990)

2) A theoretical principle deduced from particular facts, applicable to a defined group or class of phenomena, and expressible by a statement that a particular phenomenon always occurs if certain conditions be present (Oxford English Dictionary as quoted in Futuyma, 1979).

3) A set of observed regularities expressed in a concise verbal or mathematical statement. (Krimsley, 1995).

I highlighted #3, as you can see.
Krimsley was (or is) Victor S. Krimsley, the author of Introductory Chemistry. I haven't read the book, but I searched the Google Books page on it for his definition, and it is in that book.
I'm not taking sides on whether he is correct or not. I'm just fanning the flame.

 

[MrAl]

Hi Ron,

Ah, you got sucked in too i see. You can never leave now

I think maybe part of the problem is that we take some words too strongly, to mean too much, like the word "Law". Of all the words 'Law' is probably the strongest over 'hypothesis' and 'theory' so we like to have something associated with that word mean a little more than the other two. In this changing world anything can change though, or should i say anything can be disproved no matter what kind of qualifying word it has attached to it. So perhaps it's better just to get the main idea of what is meant and not get too hung up on the words themselves.
In the words of an old friend of mine, "It doesnt matter as much as long as you know how to apply it".

One thing all the books seem to stress though is that R is a constant. If it is not a constant that device or material does not obey Ohm's Law. I think that's the key point and we can then leave the semantics to others.

 

[Ratchit]

MrAl,

One thing all the books seem to stress though is that R is a constant. If it is not a constant that device or material does not obey Ohm's Law.

Right on MrAl. If the R is the same for different voltages used, then the material obeys Ohm's law, because its resistance is linear. Ohm's law is a property of a material, not a method of calculating VIR.

Ratch

 

[meowth08]

Hi all,

May Georg Ohm rest in peace now.

 

[MrAl]

Hi,

I think if it were possible he would be happy that he is still being talked about (for the most part in a positive way) almost 200 years after he did his work.

 

[Sceadwian]

That's the thing MrAl, we're not talking about it, we're talking about trying to tell people that we're not talking about it, it's like the worst game of 'telephone' that ever became embedded in common teaching. Reality distortion field in full effect!