Talk:Ohm's law/Archive 1

message: So much BS here that no one put anything about OHM's LAW in here!
If you EE type jerks look at a dictionary, that's what should be 
here and not y'all's rhetoric.
the Law is U=I*R and the Units are  1V=1A*1Ohm as an example
:Whoever you are you need to learn to stop reading, or to skip over, material you're not interested in absorbing.  Further, this is not a dictionary.  Look at entries in several encyclopedias it you need examples of scope and style. blackcloak 07:25, 22 May 2007 (UTC)
thread_title: Old stuff not in a section

message: Energy (watts) = Volts * Amperes ought to be on here or linked from here.
:That's Joule's Law.  I don't see why it belongs here. --Heron 18:34, 27 September 2005 (UTC)
thread_title:  Power law 

message: According to Halliday/Resnick, the expression V=I*R is NOT a statement of Ohm's law. The formula applies to all devices, while Ohm's law only applies to resistors where current is proportional to the potential difference applied to it.
:That's right. Ohm's law is an experimental discovery - "V=I*R where R is a constant" - not just the equation "V=I*R". I tried to make this clearer in the article, by defining 'differential resistance' for non-ohmic devices. --Heron 22:27, 25 February 2006 (UTC)
thread_title:  V=I&middot;R 

message: "Most electrical engineers use Ohm's Law every working day."  Is there data to back this up?  What is an "electrical engineer"?  I know many "electrical engineers" (as defined by a person with an EE degree) that work only on digital circuits, as computer programmers, and as patent attorneys.  I would be willing to believe that most EEs, from time to time deal with Ohm's Law, but every working day sounds like hyperbole to me.  It should be verified or else come out.  --Lenehey 22:51, 26 April 2006 (UTC)
thread_title:  Oh really? 

message: I added the first scheme that was used in this publication.
Here the European presention was used. Later is was replaced
by the USA presentation. It is maybe not bad to give both?
Tsi43318 21:14, 9 February 2007 (UTC)
replies: text: What "scheme" are you talking about?  Do you mean schematic diagram?  The idea is to make things as simple as possible, without making it so simple that a novice can't figure out what is being communicated in a diagram. (I can tell English is not your native language, and that appears to be part of the problem.) blackcloak 06:28, 12 February 2007 (UTC)
replies: text: Dear Blackcloak, On 9 Feb I puted Vir.png from Heron back in the article. This intervention survived three users until you came. I propose to put it back for the European readers.Tsi43318 07:22, 12 February 2007 (UTC)
thread_title:  Two schemes 

message: Perhaps there should be some material added about the conventions used when actually applying these equations? I was confused for a bit while trying to apply the equation P=I^2*R when calculating the power dissipation rating needed for a resistor. For instance, if you are applying a 50A DC current across a 100 ohm resistor, without knowing the conventions used, you can easily arrive at a needed dissipation of 250,000W! It took almost an hour searching the web before I found that the R value in that equation is conventionally in KILO ohms, not ohms. Applying the correct value of .1Kohms for a 100 ohm resistor gives the correct answer of 250W. I am not entirely sure whether this should go on this page or the Joule's Law page, since they are derivative of each other and the equation I mentioned above is present on both pages.
*edited once for spelling
24.32.223.33 23:11, 2 June 2007 (UTC)
replies: text: The correct value is 250,000W, or 250kW, for the values you mention. 50A through a resistance of 100Ω produces a voltage drop of 50×100=5000 volts, or 5kV. Power dissipation from 5kV and 50A is 5000×50, or 250kW. — BillC  talk 23:18, 2 June 2007 (UTC)

text: I was talking about DC values too. However, it doesn't make any difference: AC root mean square values have the same heating effect in a resistance. It's still 250kW, whether we are talking about AC or DC. — BillC  talk 10:19, 3 June 2007 (UTC)
replies: text: BillC is correct.  Watts = amps^2 * ohms, so 250 kW is the correct answer. If that is not the value you expected, then your input data must be wrong. Tell us the problem you were trying to solve, and we might be able to help you. --Heron 11:33, 3 June 2007 (UTC)

text: Good, I'm glad that's sorted.  We should certainly state the units for all equations, where appropriate, but I would be very wary of using anything but the SI base units.  If we start saying that some equations work with kilo-this and milli-that, then we will confuse more people than we help. Forget anything you have read about milliamps and kilohms being 'conventionally' used - maybe some experienced engineers do it in work that is not intended to be read by anybody but themselves, but it is not conventional practice and we should not be recommending it.  Best wishes, --Heron 20:04, 4 June 2007 (UTC)
thread_title:  Some explanation of conventions needed? 

message: using ohms law , how much current will flow in a circuit that contains a (10V)source and a 4 K resistor?
:The answer is in the second sentence of the article.  I=V/R.  --Heron 20:04, 8 July 2007 (UTC)
thread_title:  problem 

message: Perhaps a mention should be made that Cavendish did indeed more or less find out Ohm's Law long beofre Ohm did. (only problem being that Cavendish was slightly insane and hid most of his findings).
A little copy paste from Britannica 2005 Ultimate Reference Suit DVD (article Cavendish, Henry written by Charles Süsskind):
(note: Ohm's law was the last of the importants finding that Cavendish discovered independently mentioned in the encyclopedia, so the text is not fragmented.)
Finally, in a series of experiments on various conductors, he discovered that the potential across them was directly proportional to the current through them, thus anticipating the  law enunciated by Georg Simon Ohm, a German physicist, in 1827. The last finding was the more remarkable since Cavendish had no means of measuring current and managed only by turning hisown body into a meter, estimating the strength of the current by grasping the ends of the electrodes with his hands and noting whether he could feel the shock in his fingers, up to his wrists, or all the way up to the elbows. All these researches were subsequently repeated, after the discovery of his notebooks and manuscripts overa century later, by the great Scottish mathematical physicist,  James Clerk Maxwell, who devoted the last five years of his life to the task and published an annotated version of the electrical papers of Cavendish in 1879.
200.105.223.94 00:56, 29 July 2007 (UTC)
thread_title:  Cavendish 

message: Hello,
I'm not a Wikipedia editor, nor a subject matter expert, but I'm pretty sure the references to "your mother" and other crude verbage inserted in the text of this page are not actually related to ohm's law.  Perhaps the page can be rolled back to an earlier state?  —Preceding unsigned comment added by 207.218.88.215 (talk) 18:47, 4 December 2007 (UTC)
thread_title:  This page needs to be cleaned up- crude references have been inserted 

message: It is common usage to say that a current flows through a resistor.  While it may be a stricltly correct way to say that moving charge in a resistor is current through a resistor, it does not convey, especially to a young reader, the sense of a flow of something through an electrical device like a resistor.  I think it would be better to return to the use of the flow.  blackcloak (talk) 00:29, 22 March 2008 (UTC)
replies: text: I agree that "flow" is a good word to use here. However, some educators say the "common usage" of the phrases "flow of current" and "current flows" is unnecessarily confusing to learners, and leads to common misconceptions. How can we use the useful word "flow" without saying things that are misleading? --68.0.124.33 (talk) 20:09, 10 December 2008 (UTC)
replies: text: Well, "flow of current" is confusing because it is intended to mean "flow of charge".  Why not say what's intended? Dicklyon (talk) 23:10, 10 December 2008 (UTC)
thread_title:  Use of the word flow, as in a current that flows through a resistor

message: I am quite unhappy with the physics section.  It seems quite perverse, if not downright wrong, to derive Kirchoffs laws from Ohm's law.  In any case it does not belong in this article and I think it should be deleted.  Are there any other opinions on this?
What does belong in a physics description of Ohm's law is a derivation of the law from the physical (electronic) properties of conductors.  I am not proposing inserting that in this article either as it is going to be too advanced, both mathematically and physically.  But maybe a seperate article with jsut a mention of the result and a link here? SpinningSpark 19:22, 22 March 2008 (UTC)
thread_title:  Physics section 

message: You have lost the diagram from the 'how engineers use .  . . ' section.  Was this deliberate (I never liked that diagram).  If it was, the text is still referring to a diagram that is no longer there.
:That was an accident, but I agree it's an awful image, and the essay about it is unsourced and not very helpful, so out it goes.  If someone wants to do a better job of showing a typical nonlinearity to which Ohm's law does not apply, that might be OK. Dicklyon (talk) 15:16, 31 March 2008 (UTC)
thread_title: diagram

message: What you have done to the ac section is correct but there is a slight difficulty.  The s operator represents the Laplace transform operator used in the general case of transient circuits.  We are no longer describing (only) ac circuits so the heading is invalidated.  Under steady ac conditions (or a linear supersition of sinusoids) the s operator can be replaced with the jω operator. oops just noticed you said just that at the end of the section - still the heading does not quite gel with the content.
:It is not necessary to introduce Laplace transforms to use complex exponentials parameterized by s.  That's why I found a ref that does it that way. Dicklyon (talk) 15:12, 31 March 2008 (UTC)
replies: text: Oh no, I was not suggesting introducing a discussion of Laplace transforms into the article - that would be going in entirely the wrong direction.  I was only suggesting that by introducing the s operator the section heading is now wrong.  While only the jω operator was being discussed the heading "AC circuits" was appropriate.  Now the section has become more general I think it should be something like "Transients and ac circuits" perhaps. SpinningSpark 19:41, 3 April 2008 (UTC)
thread_title: s operator

message: Wonderful - you have got that down to the essentials.  I don't think that there is any longer a need to remove this to another article.  I still think ,though, an article on the physics of Ohms Law is needed which I might write one day when I have finished the dozen or so other articles I currently have in progress.
SpinningSpark 08:34, 31 March 2008 (UTC)
replies: text: I just took out the long proof that was irrelevant, wrong, and unsourced; I left the physics as it was. Dicklyon (talk) 15:13, 31 March 2008 (UTC)
thread_title: Physics section

message: These are notes I developed to help people understand Ohm's Law (use any of it if it will be useful) I also created pictures for the examples and I used the Ohm's law statement from the wiki for my notes:
A Layman’s Introduction to Ohm’s Law.
Ohm’s law states:  the current through a conductor between two points is directly proportional to the potential difference across the two points and inversely proportional to the resistance between them.
With voltage (V) constant, we find that current (I) varies indirectly proportional to the amount of circuit resistance (R).  The formula that most closely represents Ohm’s law is I=V/R, this formula can be rearranged to be used to solve other problems related to circuit analysis.
As a crude example, we will consider voltage (V) being the amount of pressure available by your water company for a water hose, current (I) being the rate of flow of water and resistance (R) being how much you open or close the water valve on the hose.  Let us consider that the pressure available for the water hose is constant and that the ratio of water flow will be directly proportional to how much we open or close the water valve.
In Examples 1 and 2, the water company provides a constant pressure of 10 volts (V), the water valve at 1/10th open is equivalent to 10 Ω (more resistive then fully open) and fully open to be 1 Ω (less resistive then fully closed or 1/10th open).
Example 1, let us open the water valve to 1/10th open and calculate the amount of current flow through the valve as measured by I.
I = V/R
I = 10V/10 Ω
I = 1 amperes
Example 2, let us now open the water valve to fully open and calculate the amount of current flow through the valve as measured by I.
I = V/R
I = 10V/1 Ω
I = 10 amperes
We should have found that a decrease in R from 10 Ω to 1 Ω was indirectly proportional to the calculated value of current (I) from 1 amperes to 10 amperes.  With voltage (V) constant, an increase in resistance (R) will decrease current (I) and a decrease in resistance (R) will increase current (I).
Now, with resistance (R) constant, we find that current (I) varies directly proportional to the amount of applied voltage (V).
In Examples 3 and 4, the water company provides a different water pressure at different times of the day, it is 10 volts (V) in the morning and 5 volts (V) at night, the water valve will be fully open at 1 Ω at all times.
Example 3, it is morning, with the water valve fully open; we wish to measure the amount of current.
I = V/R
I = 10V/1 Ω
I = 10 amperes
Example 4, it is morning, with the water valve fully open and we wish to measure the amount of current.
I = V/R
I = 5V/1 Ω
I = 5 amperes
We should have found that an increase in voltage was directly proportional to the current.  When we halved the voltage the current was halved.AnthonyBeavers  —Preceding undated comment was added at 19:05, 31 December 2008 (UTC)
thread_title: Suggested text

message: I'd like some history - what did Ohm actually say about his experiments? A description of his methods would be fascinating - I gather he used thermocouples as a current source because batteries at the time weren't stable enough. Was anyone at the time proposing a relation other than V=IR ? --Wtshymanski (talk) 16:24, 18 January 2009 (UTC)
replies: text: I bet you can get an interesting historical look from ref 12, but it costs money.  Or see this book.  Dicklyon (talk) 22:40, 18 January 2009 (UTC)
thread_title: History

message: Dicklyon, I've only just realised that you tagged this section while I was still re-writing it.  Sorry, I thought it was an old tag when I deleted it.  You said in the edit summary you wanted to delete that section if it is not referenced.  Although I have now referenced it, I agree that it does not really fit in the Ohm's law article.  I would be agreeable to it being moved to the resistance article with just a a brief link here.  I don't think it should be deleted altogether, it is definitely a commonly used engineering approximation technique and there are many references.  Neither electrical resistance nor resistivity currently cover it. SpinningSpark 18:17, 19 January 2009 (UTC)
replies: text: I have no objection to it if you have sources that connect it directly to Ohm's law.  Otherwise, the more extensive discussion in electrical resistance should be the place for this sub-topic. Dicklyon (talk) 22:32, 19 January 2009 (UTC)
replies: text: No, the sources do not support it being connected with Ohm's law (and neither do I).  They just support the description of the effect.  I have no particular attachment to this, I was just doing cleanup on an existing section. SpinningSpark 22:55, 19 January 2009 (UTC)
thread_title:  Temperature dependance 

message: Is it empirical, phenomenological or other?
TomyDuby (talk) 05:14, 30 April 2009 (UTC)
replies: text: It was originally empirical.  Under certain simplifying assumptions about materials, it can be derived from basic physical principles.  I'm not sure what I'd call it nowadays. Dicklyon (talk) 06:18, 30 April 2009 (UTC)
replies: text: Thanks for your comment. I think there should be a sentence in the main article telling that Ohm's law is an empirical law. TomyDuby (talk) 07:19, 30 April 2009 (UTC)
replies: text: How about quoting Maxwell on that? here.  Or at least cite a modern source if you want to say it's empiriical.  like this one. Dicklyon (talk) 14:35, 30 April 2009 (UTC)

text: On the other hand, if you want to get into this, you should probably balance it with statements of how Ohm's law can be derived from microphysics, at least for some materials like metals, as here or here. Dicklyon (talk) 14:43, 30 April 2009 (UTC)
thread_title:  What kind of law is Ohm's Law? 

message: I've been thinking more about this since last night.  Since no one has responded yet, let me throw out something more bold, perhaps this goes too far, but in the interest of people not developing a preconceived notion that I must be a function of V or V must be a function of I, let me propose this opening statement and set of opening equations, with the equations listed in the order of most common to least common citation in modern texts:
Start of quote:
Ohm's law applies to electrical circuits; it expresses[1] a directly proportional relationship between the voltage across a conductor and the current through it, the constant of proprortionality being called resistance.  Ohm's law may be written mathematically as:
:V = IR \qquad \text{or equivalently} \quad I = \frac{V}{R} \quad \text{or} \quad R = \frac{V}{I} 
where ...
End quote
As justification for the above statement of Ohm's law, here is a quote from p. 733 of Lerner (ref [1], a physics textbook):
"Any relation that expresses the proportionality between i and V, including Equations 27.5a and 27.5b, is called Ohm's law."
Their equations 27.5a and 27.5b are:
27.5a: i \propto V
27.5b: V = iR \ 
Have I gone too far? Waveguide2 (talk) 00:36, 19 May 2009 (UTC)
replies: text: Like I said, I prefer the more traditional statement of what Ohm's law is.  Dicklyon (talk) 01:06, 19 May 2009 (UTC)
replies: text: OK, there is certainly historical precedent for that form. What about moving of the 3 equations out of the Circuit analysis section and into the intro as I proposed last night? (I = V/R could be listed first as shown) Waveguide2 (talk) 01:51, 19 May 2009 (UTC)

text: Having heard no objections over the past week, and since (as I said above on 18th May) I think we would all agree that all 3 forms apply to more than just "circuit analysis", I will move these to the intro, but preserve the form "I = V/R" as the leading definition, listing the other two as equivalent forms after it, and also will preserve the references that are now associated with each form.  I will then check back here for any comments. Waveguide2 (talk) 15:02, 26 May 2009 (UTC)
replies: text: Like I said, I object to having those all in the lead; they're just distracting from what the law is. Dicklyon (talk) 15:13, 26 May 2009 (UTC)
replies: text: Sorry I did not see your latest comment until after I saved the page.  Is there some way that we can unobtrusively have all 3 forms in the intro rather than only in the circuit analysis section?  It seems more compact that way, and I would not want people to think that the other forms are only applicable to circuit analysis.  Please take a look at the current page and see whether you think it is too distracting. Waveguide2 (talk) 16:01, 26 May 2009 (UTC)

text: Sorry I missed your previous comment asking for feedback. I really don't see the value of having all three forms of the equations. If readers can't figure it out themselves, then we might as well like to an article on algebra. I'm with Dicklyon on this - it's too distracting. -Roger (talk) 17:38, 26 May 2009 (UTC)

text: Not in the lede - I thought that had already been agreed. SpinningSpark 18:24, 26 May 2009 (UTC)

text: Message received.  If I had this kind of response to my question of 01:51, 19 May 2009 (UTC)
thread_title: Arbitrary editing break