Talk:Electrical resistance and conductance

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various things to divide up right now[edit]

We are going to discuss this page. This page is about what electrical resistance is. Electrical rsistance is measured in ohms. The way it explains is very complicated. Electrical resistance is the flow of electricity or the current of electricity.

Something is wrong with that last sentence above. On the article, the term negative resistance doesn't seem right to me. A negative resistance would flip the current or voltage (but not both). Does the author mean negative resistivity with respect to some other value, such as temperature? Rich

What's this ? Someone wrote Ohm's law-but, it's only for DC, not AC where you got sine and other things. Look at some basic physics (or electromagnetism, or electrical engineering) textbook, for Chrissake.Mir Harven 16:10, 13 Apr 2004 (UTC)
ohms law works for a resistor whether the cuircuit is DC or AC. It can also be used with inductors or capacitors by using phasors and impedences represented by complex numbers. Neither of theese requires use of sine and cosine Plugwash 14:07, 8 Dec 2004 (UTC)
What was wrong with the version from 22:56, 3 Dec 2004? The most recent edit even omits the mention of ground, or even a reference point, without which the concept of resistance is hard to understand or measure.Ancheta Wis 18:14, 8 Dec 2004 (UTC)
measuring with respect to an arbitary reference point seems far mroeo confusing to me than just stating the voltage accross the resistor. I have NEVER seen a book that uses votlages relative to an arbiary reference point in its basic description of the rule

My mental model is

  • A - a voltmeter with a red lead and a black lead.
  1. touch the black lead to point 0, say ground
  2. touch the red lead to point 1, say the bottom of the resistor (closest to ground)
  3. V1 = the reading from the voltmeter.
  4. touch the red lead to point 2, say the top of the resistor. but keep the black lead at the same point 0. It is the reference point.
  5. V2 = the reading from the voltmeter.
  6. V2-V1=voltage across the resistor.
  • B - Now get a current meter, and measure the current draw.
  1. I = the reading from the current meter
  2. R=(V2-V1)/I

If the books don't say this, you need better books. And you might hurt yourself if you don't know the basics and you can't even measure the voltage and current. Be careful during the measurement. Try to use one hand if possible, and an alligator clip to the reference point. Ancheta Wis 00:56, 9 Dec 2004 (UTC)

I wrote this without knowledge of how you chose your user-name; it is ironic that you should choose this topic to edit. Take care. Based on the evidence, I am reverting to 22:56, 3 Dec 2004. Ancheta Wis 10:55, 9 Dec 2004 (UTC) P.S. it looks like some references to electrical safety and natural hazards are in order for this article and the related set of topics.
ahh the source of my username...long time ago...i was much younger and less ensible then
i can see what you are getting at but isn't it far simpler to just measure the voltage accross the resistor directly (that is red lead to one end blkack load to the other read off the voltage (V) accross the resitor directly then R=V/I)? not to mention more accurate as well (especially in an AC system or if the value of the resistor is small) I can see uses of your method if you are trying to figure out a lot of things about a cuircuit or possiblly if you are workign on dangerous voltages and therefore are working one handed but for the initial introduction of the formulae it is just overcomplicating things. Plugwash 11:58, 9 Dec 2004 (UTC)

The better books describe it simple first. Add my vote that it's counterintuitive and confusing to begin the explanation of a simple voltage drop with its definition as the difference between two differences between two points and a completely arbitrary and irrelevant third reference. The potential across the component is a single dimension, and it should be given as such. It would be perfectly fine to include the difference formula as an additional way of explaining it though.

I also don't consider it necessary to elaborate on practical issues in any article whose main topic should be the abstract definition of a physical property. Concrete safety-related issues about measuring instruments and their use aren't specific to resistance. A simple link on electrical safety in the 'see also' section should suffice, if any. Femto 14:43, 9 Dec 2004 (UTC)

Is there any reason why is not mentioned in this article?

added links in the caption to the resistor image --Ancheta Wis 08:54, 3 May 2006 (UTC)

Resistivity and Salt Water[edit]

The article says resistivity varies "greatly" with salt concentration. Would anyone care to quantify that? There is math there and I think worth while mentioning ionic v. covalent bonding and how salt and dirt change the bonding properties of water. How about a source? Anyway I was just looking for the actual formula and dissapointed not to find anything. Wiredrabbit (talk) 18:47, 9 December 2008 (UTC)


My father wants to know what resistance have 5ppm of silver ions in water. He needs the number and the formula. Does anyone know how to calculate this? Thanks. --Eleassar777 17:03, 1 Jun 2005 (UTC)

Measuring resistance[edit]

I think that by definition, measurement of the resistance of a conductor would assume that the proper terminations had been made from the measuring device (ohm meter, mutimeter etc) to the resistance under measurement. I therefore think that the statement about c'ompletly covering the ends' is superfluous.

Does anyone agree or disagee??Light current 20:34, 1 August 2005 (UTC)

What do you define as 'Scattering events' in a wire? -Grim- 10:40, 27 March 2007 (UTC)

External links[edit]

I removed the convertor links (including four to the same friggin' site), per WP:NOT. I left this one, as it actually has some information that may add to the article, describing the magic triangle. However, I won't cry if someone delete that one too. —johndburger 02:37, 10 June 2006 (UTC)


Does anyone know how resistance is used? It may seem like a stupid question but i'm only in junior high.

Matt S.

—The preceding unsigned comment was added by (talk) 00:49, 29 January 2007 (UTC).

Think LEDs, my friend. 9V batteries are commonly used in robotics, and you need at least a 150 ohm resistor to power them directly from it. And It's not a stupid question, no question is. 18:59, 5 February 2007 (UTC)
do you think there would have been any appliance if it weren't for resistance? I do not think so. what is your point?


Now how does temperature effect resistance? No math, just explain how it works. Pls and thx. 19:00, 5 February 2007 (UTC) Temperature affects the micro-vibration of the ions within the conductor. The more the ions vibrate, the more electrons are dissipated due to the effect discussed in the article. Matwilko 00:55, 20 February 2007 (UTC)

U-I Graph?[edit]

The negative resistance section refers to the U-I graph. Shouldn't this be V-I graph? (voltage vs current)? Billgordon1099 (talk) 17:54, 1 May 2008 (UTC)

Yes, you are right, it should be a V-I graph. But even this is not good enough: In semiconductors (for example diodes) one typically uses the term I-V characteristics. TomyDuby (talk) 05:09, 10 August 2008 (UTC)

Why? in that case it must be V-C not V-I it is most likly some misprint since V looks like U —Preceding unsigned comment added by (talk) 23:27, 30 September 2009 (UTC)


According to the NIST Guide to SI Units:

6.1.2 Capitalization
Unit symbols are printed in lower-case letters except that:
(a) the symbol or the first letter of the symbol is an upper-case letter when the name of the unit is derived from the name of a person...

Since the unit for resistance (the Ohm) is taken from Georg Ohm, shouldn't the unit be capitalized in all Wikipedia articles? —Preceding unsigned comment added by Jcarroll (talkcontribs) 18:43, 2 July 2008 (UTC)

Yes, the "unit symbol" should be capitalized, but not the "unit name". I agree that it would be more consistent to make both the name and the symbol uppercase for all SI units named after a person. Alas, that's not what the standard says.

My reading of the guide you mentioned (in particular the section on "Rules and Style Conventions for Spelling Unit Names") implies that:

  • The "unit symbol" for resistance (Ω) should be uppercase.
  • The "unit name" for resistance (ohm) should be lowercase.

That "NIST Guide to SI" seems consistent with the Wikipedia:Manual of Style (dates and numbers)#Unit symbols here, which says

  • Units named after persons are not capitalized when written in full (write A pascal is a unit of pressure, not A Pascal is a unit of pressure). This does not apply to "degree Celsius" and "degree Fahrenheit".

and is also consistent with the International System of Units article, which says

  • Symbols for units are written in lower case, except for symbols derived from the name of a person. For example, the unit of pressure is named after Blaise Pascal, so its symbol is written "Pa", whereas the unit itself is written "pascal". ...

-- (talk) 01:44, 23 February 2009 (UTC)

Deletion proposal[edit]

I request that this page be removed from Wikipedia, or at least, merged into Ohm's Law or something of that nature. It hasn't got a single source and there are several other articles discussing the same facts about electrical resistance. I am more than happy to discuss this issue... I will reply to your thoughts more promptly if you leave your post on my talk page and this section. Destroyer000 (talk) 06:26, 20 June 2009 (UTC)

I think this page should definitely be kept. With a concept as fundamental as electrical resistance, you're bound to have lots of pages that make reference to it. That other pages also discuss electrical resistance and give brief explanations as to what it is does not mean that there shouldn't be a central location where information on this topic can be easily found. Furthermore, Ohm's Law and electrical resistance are two distinct concepts. One is describing the relationship between voltage, resistance, and current; the other is the concept of electrical resistance itself. If electrical resistance should be deleted, then so should electrical current and voltage. Or perhaps Ohm's Law should be deleted, since its information is repeated on all 3 of the other pages.

I also see 7 sources directly cited on the page. There is quite a lot of useful information found here. So the quality of the page is not grounds for deletion. Lastly, Wikipedia has no lack of storage space, and it does not need to be normalized at the cost of de-optimization. Just because all the information contained here can also be found on various other pages doesn't mean users researching electrical resistance should have to scour 10-20 different pages to find all of this information. Instead, a comprehensive page on electrical resistance itself is both better organized and more intuitive to users. -- (talk) 15:27, 20 June 2009 (UTC)

Another thing to consider: Ohm's Law does not always apply. For example, a device like a silicon diode has electrical resistance, but the relationship between voltage and current is not linear. Both articles should remain. CosineKitty (talk) 14:34, 25 January 2010 (UTC)

English variations[edit]

I am restoring this article to American spelling based on WP:ENGVAR. This topic is not tied to a particular country. Also, I went back through the entire edit history and the earliest conflict between British/American spelling was this one from 22 July 2005. That predates the cited revision 41307060, which was made on 26 February 2006. The revision that changed it back to American spelling was not explained, but it was correct based on WP:ENGVAR. CosineKitty (talk) 16:15, 23 January 2010 (UTC)

The earliest revision to feature the word metre/meter is this one by Icairns on 29 October 2004, in which the former spelling is used. –CapitalLetterBeginning (talk) 15:13, 24 January 2010 (UTC)
Oops! You are right. Sorry about that. I will put it back the way you had it. (Strike-out added above by myself.) CosineKitty (talk) 20:48, 24 January 2010 (UTC)
Thank you. –CapitalLetterBeginning (talk) 14:05, 25 January 2010 (UTC)

Fermi Level[edit]

This term is used twice, but never defined —Preceding unsigned comment added by Snirm (talkcontribs) 01:45, 3 February 2010 (UTC)

It turns out there is a Fermi level article. I linked to it from the article text. Maybe that will help some. CosineKitty (talk) 01:53, 3 February 2010 (UTC)

Suggest merge[edit]

Merge to Electrical conductivity; it's a reciprocal relationship and does not need to duplicate all the discussion there. --Wtshymanski (talk) 15:26, 13 December 2010 (UTC)

Well, not exactly. There are actually four articles:
  1. Electrical resistance
  2. Electrical conductance
  3. Electrical resistivity
  4. Electrical conductivity
The latter two describe the material's inherent property to resist current, while the former two describe the equations when applied to concrete geometry. In my opinion, 1 and 2 should be mutually merged, as well as 3 and 4 (because they're reciprocal relationships indeed)-- but not 1 and 4. Personally, I would prefer them under "resist*" titles, since those concepts are slightly better known and used in electric engineering, though I wouldn't mind the other way round either (or under compound titles such as "Electric resistance and conductance") No such user (talk) 09:11, 14 December 2010 (UTC)
At least that much merging, but I think the reader's interests would be better served by one article on electrical conduction, with about a paragraph explanation for each of these other terms. Better to put all our carefully annotated brilliant prose describing the physics of conduction bands and Fermi levels in one place, rather than scattering it through four articles with mutually contradictory and incomplete descriptions. --Wtshymanski (talk) 14:18, 14 December 2010 (UTC)
On reflection, you're probably right. Still, I wouldn't put electric conduction into this equation, although it might be mergeable with electric current. No such user (talk) 15:48, 14 December 2010 (UTC)
I agree with "No such user" -- let's go ahead and merge 1 and 2 into one article now, and 2 and 3 into another article now. Likewise, I don't particularly care which title is used.
Later, after we've reduced these 4 articles to 2 articles, then we can talk about the possibility of further merging. --DavidCary (talk) 17:37, 22 January 2011 (UTC)

I agree with No such user: Merge 1 with 2 and 3 with 4. I personally would prefer the compound titles, otherwise some editor will probably re-start the articles that we are deleting. Actually I think the ideal solution in this case would be to separately improve all of the articles, copying-and-pasting sections as necessary...but that's harder to do and harder to maintain. No merging with electric conduction, it's different. --Steve (talk) 18:09, 22 January 2011 (UTC)

I would like to register another vote for merging Electrical resistance with electrical conductance and Electrical resistivity with electrical conductivity. I teach electricity and magnetism at the freshman, junior, and graduate level. My doctorate is in solid-state physics. I concur with the discussion that resistivity and conductivity can be considered about intrinsic material properties and responses of materials to temperature, doping, etc. Resistance and conductance are linearly dependent on resistivity and conductivity, but they can be considered as properties of electrical components, or of electrical measurements with a fixed geometry. All the concepts are so basic and so widely useful that a single article would be perhaps too long. At the same time, it does seem silly to have separate articles on quantities that are reciprocals of eachother. There are certain "users" of resistivity vs. conductivity measurements. It seems chemists and water-quality people like conductivity, for example, while electrical engineers might be more likely to use resistivity. This can be pointed out in the merged articles.

I also support maintaining the "Electrical" before the other terms. Equations for thermal conductance and conductance of pipes to water flow (see Hydraulic analogy) are essentially identical to Ohm's law, but they are used by different people and there are different measurements to characterize them, so it is better IMHO not to just have one article called "conductance" which would then have to cover far too much material. Pcardout (talk) 01:28, 23 January 2011 (UTC) (see "hydraulic analogy")


I merged Electrical resistance and Electrical conductance into Electrical resistance and conductance, as well as Electrical resistivity and Electrical conductivity into Electrical resistivity and conductivity. While further merging is perhaps possible, I felt that this is not the current consensus, and that the resulting article could be overlong. Take it on from here.

There are probably more candidates for similar merging, such as Electrical impedance and admittance, or Electrical reactance and Susceptance. Later... No such user (talk) 12:00, 24 January 2011 (UTC)

Resistance matrix and conductance matrix[edit]

Is it a good idea to include resistance matrix and conductance matrix in the article?--LaoChen (talk) 01:33, 24 February 2011 (UTC)

No, it is too specific subject. However, we do have an article Nodal admittance matrix, which is in a very poor shape, and should be more prominently linked. No such user (talk) 07:34, 24 February 2011 (UTC)

More merging[edit]

Somone pulled the template off at Electrical resistivity and conductivity. I very much doubt the treatment of the subject on Wikipedia will be subtle enough to need two articles covering the same material, and I suggest they be merged. --Wtshymanski (talk) 16:02, 11 August 2011 (UTC)


The beginning of the article calls the conductance the "the inverse quantity" of the resistance. Later it is written that: "For purely resistive circuits conductance is related to resistance R by G=1/R. For practical reasons, any connections to a real conductor will almost certainly mean the current density is not totally uniform. However, this formula still provides a good approximation for long thin conductors such as wires." How is the conductance defined, if not by G=1/R? Why should this depend on whether the circuit is purely resistive (if you think about capacitors and inductances: Admittance is _defined_ as the inverse of the impedance)? How is a non-uniform current density related to this definition (R is by definition an average quantity. Can one even define a "local" resistivity?)? Is the relation G=1/R wrong for "thick" conductors? — Preceding unsigned comment added by (talk) 17:45, 28 November 2011 (UTC)

This must be referring to the expresion of resistance in terms of resistivity and not the the formula R=1/G. Probably got separated in the process of merging resistance and conductance articles. SpinningSpark 22:35, 30 November 2011 (UTC)

Sources of resistance in metals???[edit]

The article state "The larger the cross-sectional area of the conductor, the more electrons are available to carry the current, so the lower the resistance." I'm not an expert on the subject but this does not seem like the proper reasoning to me. There are indeed more electrons, but the are also more ions in the lattice to scatter them. I always thought it is a surface effect. I thought the abrupt ending of the organized lattice at the surface is a cause for resistance. Though the surface becomes larges as the cross-sectional area of the conductor increases, it does so slower than the area of the conductor (for instance for a circular cross-section the surface increase like 2*pi*r while the area increase like pi*r^2. Can an expert look into this. Maybe it is better to remove the sentence in the meantime?

In addition is the room for the highschool formula in this section?Eranus (talk) 16:54, 7 December 2011 (UTC)


It's correct as written. More electrons means each electron only needs to travel half as fast to carry the same current. So each time they scatter, they lose less energy.
Let's say a wire is a cylinder. It has round walls along the length and flat walls at the ends. I'm not sure which surface you're referring to as being important.
The round walls are the source of "surface scattering", but surface scattering is only important if the wire is very small, like 10 nanometers in diameter. For a macroscopic wire, surface scattering is negligible, and that's why the resistance is inversely proportional to cross-sectional area not cross-sectional circumference.
The flat walls at the ends can be important too, scattering there would be classified as a type of "contact resistance". When you discuss the resistance of a wire, it usually implicitly excludes the effect of contact resistance.
The formula relating resistivity to resistance is already in the article, isn't it? --Steve (talk) 18:19, 7 December 2011 (UTC)

reorganized and moved content[edit]

As pointed out in previous discussion, there was not much logic behind what topics were covered in this article versus what topics were in electrical resistivity and conductivity. In reorganizing and rewriting, I moved a lot of content from here to the other article, where it is a better fit to the topic. I don't believe I deleted anything important. I believe that I put sufficient cross-references and links that readers will not have any difficulty finding the content that they are looking for. I hope other people agree, and I hope everyone looks carefully through the articles for any problems I created or mistakes I made. Thanks!! :-) --Steve (talk) 17:40, 9 December 2011 (UTC)

Be careful of what you ask for. Here are my thoughts ordered roughly in order of importance to me:
  1. good work
  2. you took too much out of the temperature dependence of Resistance. (It is an important property of resistors and therefore of resistance). My suggestions:
  • move temperature dependence out of resistivity and just before strain dependence
  • low temp dependence is not needed but I think basic linear dependence R = Ro(1-α(T-To) is important. A small table or link to typical α may (or may not) be appropriate.
  • some expansion of themistor and resistance thermometers may be appropriate (or not?). To me the section seems too short and technical for the importance of these devices. Opinions may vary.
  1. Move AC circuits to bottom. It just is not as closely related to resistance as the other sections, in my opinion, and is the most difficult to understand.
  2. Move typical resistance section and measuring resistance section up to near the top and expand. In my mind these are two of the most defining characteristics of this article.
  3. You did not cut enough from resistivity. I don't think much more needs to be said other than the relation between resistivity/conductivity and resistance/conductance and the fact that the resistance/conductance of an object can be set by choosing appropriate materials and dimensions.
  4. To help link articles I prefer to use the about template like {{about|a property of objects describing how well electricity flows through them|a property of materials describing how well electricity flows through them|electrical resistivity and conductivity}}
  5. On an unrelated note, I did not see superconductors in the article.
  6. Another unrelated note, a little expansion of Impedance may be appropriate. Resistance is an article that should be geared for a little lower technical level audience than a typical article, in my opinion. Either take a few more sentences to explain it better or cut it down to the fact that it exists without the equations.
  7. keep up the good work

TStein (talk) 19:51, 9 December 2011 (UTC)

Thanks! I agree with most, or probably all, of these. (Most of these are not my fault!) I hope to chip away at them, as time permits.
For the resistance table, I can't think of any other suitable entries besides the four there now. Maybe someone else can think of some... :-) --Steve (talk) 21:38, 11 December 2011 (UTC)
I figured that most of those were probably there already. But, I was going to evaluate it I might as well do it right. As far as the table, I had some ideas before, but I wasn't smart enough to write them down. TStein (talk) 04:11, 12 December 2011 (UTC)
My list of other things that could be done...
  • Series and parallel circuits summary (maybe not sufficiently important)
  • Output impedance, Input impedance summary (probably not sufficiently important)
  • Plots of some ohmic and non-ohmic IV curves: Large resistance, small resistance, battery, diode
  • Nonlinear IV curve with differential resistance and chordal resistance drawn in
  • More details about ohmmeters (maybe not sufficiently important beyond one or two sentences)
  • Summary of joule heating, i.e. the fact that pushing current through a resistance dissipates energy
--Steve (talk) 15:37, 13 December 2011 (UTC)

"R=1/G always for a given element in a circuit"?[edit]

Spinningspark writes "R=1/G always for a given element in a circuit". Can you please explain this? Are you disagreeing with "R is the real part of Z, G is the real part of Y"? Or are you saying that "a given element" must be an ideal resistor? An ideal capacitor has R=G=0, so R=1/G is not true. Is an ideal capacitor not an "element"?? A real resistor or wire(as opposed to an idealized resistor) has a nonzero reactance, so R=1/G is not true. Is a real resistor or wire not an "element"?? --Steve (talk) 12:57, 24 December 2011 (UTC)

UPDATE: OK, I guess a real resistor is a "component" not an "element". I'm still confused about the ideal capacitor. Also, it seems to me that readers may be naturally thinking in terms of components rather than elements if we don't clearly state otherwise.

On a perhaps-related note, you wrote "The impedance and admittance may be expressed as complex numbers". May be? I thought, impedance and admittance are complex numbers. Right? --Steve (talk) 13:30, 24 December 2011 (UTC)

Where I am coming from with this is that Z=R+iX and Y=G+iB while they may be equal to the same impedance are not represented by the same network. An impedance consisting of a resistance R1 in series with a reactance X1 is given by Z=R1+iX1. A conductance G1=1/R1 in series with a susceptance B1=1/X1 has the same impedance Z. However it is decidedly not true that the admittance Y=1/Z is equal to G1+iB1.
At the risk of now boring you with repetition, the dual of this is that an admittance consisting of a conductance in parallel with a susceptance is given by Y=G2+iB2. The resistance of the conductance is R2=1/G2 and the reactance of the susceptance is X2=1/B2. It is decidedly not true that Z=R2+iX2.
The former claim in the article amounts to saying that R1≠1/G2. Well of course it doesn't, R1 and G2 are not the same element. The first is the resistance from a series equivalent circuit and the second is from a parallel equivalent circuit. It is however always true (by definition) that the conductance of element R1 is always 1/R1 and the conductance of element R2 is always 1/R2.
On the "...may be expressed as a complex number". It is certainly true that to get anywhere with a mathematical analysis of a non-trivial network it is more or less mandatory to express impedance as a complex number. However, it is perfectly possible to introduce the concept of impedance without resorting to complex number representations at all. This is frequently done on elementary electrical science/engineering courses where the mathematical training of the students is not yet advanced enough to cope with complex number manipulations but the course requires impedance to be introduced at an early stage. While much more clumsy, it is still possible. It is also true that the Z=a+ib representation is not the only complex number representation. SpinningSpark 01:42, 25 December 2011 (UTC)
If I have a wire with complex impedance Z, I personally would say: "The AC resistance of the wire is defined as the real part of Z, the AC conductance of the wire is defined as the real part of 1/Z". But it seems, you would find that statement misleading, right? After all, the "resistance of the wire" has one value if you represent the wire as a series network, and a different value if you represent it as a parallel network. I just want to understand your perspective here... :-)
For the other question: You say, "it is perfectly possible to introduce the concept of impedance without resorting to complex number representations". Well, it's true that you can describe complex numbers without calling them complex numbers. You can discuss pairs of real numbers (or a single real number paired with an angle) with certain arithmetic/manipulation rules, and you are actually discussing complex numbers by another name. So it still seems to me that if a simple textbook says "impedance is a real number paired with an angle" that does not mean wikipedia should avoid the statement "impedance is a complex number". (I suppose I need to look through some textbooks to understand better.) --Steve (talk) 22:15, 25 December 2011 (UTC)
Without getting into a big debate and answering all your points in detail (for which we should probably take the discussion off this talk page) the bottom line is that conductance is the reciprocal of resistance by its definition and to say that it sometimes isn't is not just misleading but is downright wrong. SpinningSpark 00:38, 26 December 2011 (UTC)
What about:
Often, the real part of the impedance of a component is called its "AC resistance" and the real part of the admittance of a component is called its "AC conductance". With this terminology, the "AC resistance" of a component may not be the reciprocal of the "AC conductance" of the same component.
Is this any better? :-) --Steve (talk) 13:54, 1 January 2012 (UTC)
No, it is still introducing an unnecessary confusion. The reason you do not get conductance reciprocal of resistance has nothing to do with the application of AC. The resistive part of an impedance does not change because AC is applied (putting aside skin effects and the like). It does not even really have anything to do with splitting an impedance into real and imaginary parts. It has everything to do with series and parallel representations. A similar anomaly can be constructed entirely with resistive elements. As an example, take a resistance of 1 kilohm. This can be represented with an equivalent circuit of two resistors in series: R1=R2=500 ohm. That same 1 kilohm resistance (equal to a 1 mS conductance) can be represented by two conductances in parallel: G1=G2=500 μS. No one should find it in the least bit strange that G1 is not the reciprocal of R1 and G2 is not the reciprocal of R2. It is not some anomalous exception to the definition of conductance. Yet that is exactly what you seem to be saying about impedance. I have recently been looking through Ernst Guillemin's Introductory Circuit Theory for the purposes of referencing a different article. Guillemin has some interesting things to say on this. You seem to have walked into exactly the trap Guillemin is talking about. Guillemin was a major figure in network analysis and its teaching and if he says it is a mistake to look at impedance this way then it should be taken seriously. At least find an equally notable reference who says you should explain it this way. SpinningSpark 14:52, 1 January 2012 (UTC)
Hmm. For now, I'll take your word for it. I certainly have no problem with what's currently in the article.
Incidentally, if you think anything else in the "impedance and admittance" section is misleading or unhelpful to a deep understanding, feel free to change it! :-) --Steve (talk) 18:10, 1 January 2012 (UTC)

Resistance defined at I=0?[edit]

The introductory section states: "The resistance of an object is defined as the ratio of voltage across it to current through it, while the conductance is the inverse:"

But this would suggest that resistance is undefined when I=0. Questions:

1. Assuming an ohmic ("constant resistance") component or element, do different disciplines have different conventions about how to regard resistance: Is it situational? Or is resistance regarded as a fixed property of a component or circuit element, corresponding to how resistivity is treated as a property of a material even in the absence of current.?

2. What are some circumstances where it matters whether resistance is regarded as defined or undefined at I = 0?

3. Is R = V/I perhaps not a definition, but rather just a relationship? It just provides a way to measure R, which doesn't work with I = 0?

4. Perhaps the way disciplines use the concept resistance (especially in algebra) actually implies that the definition is more like:

 R = V/I,  I <> 0
 R = dV/dI, I=0

Interested to hear what people have to say. Gwideman (talk) 03:08, 29 January 2012 (UTC)

My impression (someone can correct me if I'm wrong) is that the resistance of an ohmic component is regarded as an fixed intrinsic property of the component. For example, let's say I have a "100 ohm resistor" in a circuit. If I cut it out of the circuit and put it in a plastic bag on my shelf, it is still a "100 ohm resistor". If someone asks me what its resistance is, I would say "100 ohms", I don't say "That question has no answer as there is no current flowing through it at the moment."
For (4), see Electrical resistance and conductance#Static and differential resistance. It is certainly true that "differential resistance at zero current" is defined but "static resistance at zero current" is not. That's for non-ohmic components though. For something that's perfectly ohmic, people would not talk about static or differential resistance, they would only talk about its (fixed intrinsic) resistance. --Steve (talk) 13:17, 29 January 2012 (UTC)
Steve: My impression from several decades exposure to EE matches yours. I'm hoping for something more formal :-). In particular, clarification of whether resistance is considered an intrinsic property (whether for an ohmic component or not, or for an idealized element), whether this differs by discipline, and so on. Gwideman (talk) 09:32, 30 January 2012 (UTC)
I am completely against complicating the article with this kind of unnecessary imaginary difficulty just because the mathematicians get upset by it. I am with Heaviside on this one. Every other law in physics which involves proportionality of two variables will have the same problem when it comes to defining the constant of proportionality. Hooke's law for instance, and even Newton's second law. I would say that division by zero in this cotext would best be replaced by a limit rather than a differential, why switch from static to differential resistance just because it is near zero? Although I would not be in favour of that going in the article either. Note there are some circumstances when a limit and a differential may not give the same result at zero - a memristor for instance. The bottom line for me is that none of the sources that define R=V/I find it necessary to give a special treatment of the case I=0. Without a source, it doesn't go in Wikipedia, and doesn't get discussed here. SpinningSpark 14:09, 30 January 2012 (UTC)


Wikipedia:Naming conventions#Titles containing "and" — Preceding unsigned comment added by (talk) 23:59, 19 November 2012 (UTC)

Can you please tell us why you just posted this link? Do you object to the name of this article? Can you elaborate a bit? --Steve (talk) 22:29, 20 November 2012 (UTC)

Practical aspects of the electrical resistance as a part of the electrical network[edit]

Security and norm applications of a resistance in an electrical network: necessity of a such resistance between the electrical network and turned on devices. for computer technics and TV display (because voltage fluctuations possible) and a rectifier for a fridge. Protection against magnetization is needed, because a biological organism accumulates a static charge and PC accumulates it from an electrical network. If there is an UPS, it isn't felt by human. Eyes don't stick on the monitor, in other words, and a person reacts to its contents another way. Between a network and PC there are a lot of asynchronous events. UPS suppresses their excessive intensity (in relation to impact on a live organism). I.e. charges on a body and on the computer can strongly interact statically, if there is this resistance. I think that if electric conducting old, it can be felt more, than on new, but effect in fact the same. For the fridge - the rectifier is necessary (the rectifier will transform alternating current to constant, the UPS leaves alternating current as is, alternating current is used in networks most for transfering of the electric power to long distances. It is easier to transport it on long distances, transforming in transformers. Probably, because fridges main objective - to maintain temperature, but not online to interact with the user. Also, as far as I know, other kitchen devices (a teapot, a plate) don't recommend to include through UPS/rectifier/network filter. The standard UPS for them will have rather high electricity consumption a little therefore it is better to include them directly, but essentially and they can be included via the UPS/rectifier, simply in this case it is impractical. About network security see Why the Future Doesn’t Need Us. Seagateups (talkcontribs) 00:25, 7 November 2015 (UTC)