Talk:Electrical resistivity and conductivity

resistivity of Al

After searching other locations, I'm finding very different versions of resistivity for Al. Something closer to 2.6 or 2.8 rather than 2.282... --Hobit 14:19, 11 October 2005 (UTC)

–Fixed. I used the value from aluminium, which was taken at 20°C. This is equivilent to 293K, as used in this article). —deanos {_p^t_a^a_*^l_g^k_e} 15:18, 15 October 2005 (UTC)

References

The table of resistivity values looks exactly like the one in my physics textbook (Physics for Scientists and Engineers, with Modern Physics by Serway and Jewett). Is there a missing citation here or am I missing something? Mahsmanj

I've added references for most of the materials, and for those where I couldn't I've moved them from the article to here. I also redirected Table of resistivities here, because the table here was exactly the same.

Material	Resistivity (ohm metres)	Temperature coefficient per kelvin
Chromium	1.8 × 10-7	.0000059
Tin	1.15 × 10-5	.0042
Silver, German	3.3 × 10-5	.0004
Seawater	2.0 × 10-1 [1]	?
Pure water	2.5 × 105	?
Human skin	approximately 5.0 × 105	?

Kevin 09:30, 4 May 2006 (UTC)

German silver is also known as nickel silver. If you look for the resistivity nickel silver instead of german silver, you will have better luck finding a source. -Rudy

Volume?

Does anybody know how resistivity relates to the volume of an object? That is, if I had something that looked more like a sphere than a thin wire, and wanted to calculate its resistance using its resistivity, how would I do it?

Its wikipedia custom to sign your name with four tildes ~~~~, welcome to wikipedia. As for your question, I think you could calculate it with an integral if you really want to : ) . Start by approximating it as a series of circles with some thickness dx, where the thickness of circles in the series goes from 0 to the radius (of the sphere). Add all the resistivities of those circles up, and take the limit as the distance between different sized circles goes to 0.

That would probably be a difficult integral to figure out how to set up, but you could easily approximate it without taking such a limit. Simply approximate the sphere as say 5 different circles, and see what the resistivity comes out to. Fresheneesz 22:50, 27 May 2006 (UTC)

It probably involves integrals, though I don't know if the equations are straightforward. Remember that this isn't a straight volume or surface area type calculation. You're calculating the resistance of the object, but the resistance will be different for the same object depending on how the electrodes are arranged. Would you have to calculate the current flow through each differential cross section of the entire object? This gets into bulk resistance calculations that I am not familiar with (but would like to be). — Omegatron 19:00, 24 February 2007 (UTC)

The total resistance of a body is not just determined by its volume, but the area of the contacts (contact points). If you know the volume of the body, and the area of the contacts, then you can calculate the bodies "relative resistivity length" by simply dividing the volume by the area of the contacts. This will give you the value for "l". ZoftWhere 08:48, 15 March 2007 (UTC)

Performing the above-mentioned integration you can calculate the resistance for a sphere with radius r connected with opposite round contacts that penetrate a depth d (0<d≤r) into the sphere. The integration yields:

$R={\frac {\rho }{2\pi r}}\ln {\frac {2r-d}{d}}$,

where ρ is the resistivity of the material. Note that this is the resistance of the sphere without the end caps (i.e. contacts). Mytomi 04:51, 15 November 2007 (UTC)

19:59, 2 July 2007 (UTC)19:59, 2 July 2007 (UTC)155.104.37.17 19:59, 2 July 2007 (UTC) Sorry to add here, but I'm not seeing any better way to add a comment to the page.

Resistivity may also change under many conditions besides temperature. Humidity, for instance, as a material absorbs water, or even in a vacuum, where it outgasses whatever material. This is an effect we have seen before - nylon is a good example, it's resistivity goes up under a vacuum.

combining resistivity and conductivity tables

I think it would be better if we combined the tables of resistivity and conductivity since they are so fundamentally linked. Please discuss this at Talk:Electrical conductivity. Fresheneesz 22:52, 27 May 2006 (UTC)

Resistivity equation

somebody has just defaced the general equation: it should be rho=R multiplied by A divided by length

The general equation is incorrect

I have changed it twice but someone keeps changing it back. It should be

${\rho ={R\left.{\frac {l}{A}}\right.}}$

and not

${\rho ={R\left.{\frac {A}{l}}\right.}}$

I do not make out that I understand everything that is involved with resistivity as I am only a year 11 pupil studying it for my GCSE but about this I am quite certain and I have also verified it with my teacher. Some one told me to check this up on an External sitewhich I did. There equation of

${\ {R=\left.{\frac {\rho l}{A}}\right.}}$ is the same as ${\ {R=\rho \left.{\frac {l}{A}}\right.}}$

which can be rearranged to form

${\rho ={R\left.{\frac {l}{A}}\right.}}$

If anyone can explain why it should be the other way please try. Mrpowers999 16:16, 24 February 2007 (UTC)

If someone keeps reverting your edits, there's probably a good reason for it! Don't keep making the same edits without discussing it!

Your math is wrong. You say:

${\ {R=\rho \left.{\frac {l}{A}}\right.}}$ which can be rearranged to form ${\rho ={R\left.{\frac {l}{A}}\right.}}$

but this is incorrect. Think of it this way. Divide both sides by L and multiply both sides by A:

${\ {R=\rho \left.{\frac {l}{A}}\right.}}$ which can be rearranged to form ${R\left.{\frac {A}{l}}\right.=\rho .}$

Also you should know that your equation is wrong because the units don't come out right. The correct units for resistivity are Ω·m. If you divided length by area you would get Ω/m.

Please be more careful when editing if you aren't sure of something. — Omegatron 18:32, 24 February 2007 (UTC)

I got out the old pencil and paper and realised you were right :( This will mean a few ammendments to my physics coursework 'sigh' Mrpowers999 00:50, 25 February 2007 (UTC)

If you are really eleven, don´t worry about the errors in math, but Omegatron is correct: you should be carefull because people will trust the precission of the information you post ( I did, until I cared to think twice). I would like you to forget about math and think about physics, (as an electron), while you travel bumping "against" atoms. The more length of the material means more bumps, the more surface of material means more paths to travel. So "resistance" to your travel is directly proportional to length , and inverselly proportional to surface.Resistivity comes to be a property of the material ,an indication of how difficult is to travel appart from length and surface.So your "resistance" is directly proportional also to this property called resistivity. If you want to express resistivity , all this thinking has to be expressed the other way around. Omegatron gives you a good indication, always check the units that come out of the math . They will help you to tell if your reasoning can be right.Keep your chin up, and make this page perfect.--Angel 13:22, 14 July 2007 (UTC)

The current induced by an electric field is more generally defined by J = σ E where J = I/A is the current density (amps/m²), σ is the conductivity (mhos/m) and E = V/L is the electric field (volts/m) with J and E being vectors. ρ (ohm-m) is defined as 1/σ so that (J/σ = ρ J =) ρI/A = V/L (= E) which in turn gives ρ = VA/IL = V/I A/L = R A/L.

Hence ρ = R A/L or R = ρL/A.

So the resistance R of a wire of resistivity ρ is proportional to its length L and inversely proportional to its cross-sectional area A. --Jbergquist 05:24, 14 October 2007 (UTC)

For the analagous situation of the flow of fluids through tubes subject to a pressure difference see Poiseuille's law. --Jbergquist 09:12, 14 October 2007 (UTC)

Hydraulic analogy — Omegatron 16:50, 14 October 2007 (UTC)

Perhaps it would be better to define the resistivity implicitly: ρ is a coefficient chosen so that R = ρ l / A? It's a bit round-about, but it's more intuitive; we expect the resistance to increase with length and decrease with cross-section. --catslash 18:12, 14 October 2007 (UTC)

Nov 27, 2007 I corrected the units for resistivity from Ohm-meters to Ohms per meter. —Preceding unsigned comment added by 206.104.31.54 (talk) 01:24, 29 November 2007 (UTC)

Why did you do this ? Omegatron is definitely right. The only possible unit is Ohm.meter. Check the formula that is on WP at the moment (p = RA/l), check the formula given on the external site in the first comment (R = pA/l), or check the wikipedias in other languages. Jérôme (talk) 18:34, 29 November 2007 (UTC)

NB: In the UK, Year 11 is the final year of compulsary education. Mrpowers999 will be either 15 or 16, NOT 11. This is because school starts at 4 or 5 (not birth) and the first school year is called reception. Anonymous —Preceding unsigned comment added by 79.71.27.222 (talk) 18:23, 23 November 2008 (UTC)

Is the table correct?

I think either the table is wrong, or the values in the Silver, Copper and Gold articles are wrong. Also, considering that the resistivity is given with much less precision than the coefficient, it seems misleading to add 1.47... to ~.0038... and get ~1.4738.... Κσυπ Cyp   13:06, 23 April 2007 (UTC)

Except for silver (which I reckon is just plain wrong), the values here are close to values in some electromagnetics texts I have to hand. It's likely that these values are for engineering materials, which will have trace impurities, and consequently resistivities which differ by a couple of percent from those of the pure element. I would guess that even for chemically pure metals, the resistivity would depend somewhat on the material's history (whether it had been worked, annealed or tempered).

Regarding the temperature coefficient, this could be of interest, even if smaller than the precision of the constant term: it quantifies the difference in resistance between two similar bits of metal at different temperatures (which could be used to measure a temperature difference using a Wheatstone bridge). Also it puts a bound on the variation with temperature, even if only to indicate that it's too small to worry about. I don't like the nones though. --catslash 15:16, 1 May 2007 (UTC)

Huh????? A temperature coefficient of 0.0038 is pretty damn significant if there's a delta-t of 100 K, that means the resistivity has gone up by 38%!!!- (User) WolfKeeper (Talk) 22:42, 28 June 2008 (UTC)

According to my materials text book (Materials Science and Engineering an Introduction by William D. Callister Jr.) Silver (commercially pure) at room temperature is 1.47 * 10^-8, Copper (for C11000 electrolytic tough pitch, annealed) its 1.72*10^-8, as impurities are added, it goes up. As for Commercially pure Gold its 2.35*10^-8. Hopefully this helps, feel free to PM me. ~~TheGreatCO 2:06(EST), May 7, 2007

The remark regarding the use of the coefficient is wrong, it shouldn't simply be added. The alpha value should be used as described in the "temperature coefficient" article which is also linked [AMJ] 15:14 GMT+1, May 8, 2007 —The preceding unsigned comment was added by 87.54.37.67 (talk) 13:14, 8 May 2007 (UTC).

The Al and Cu numbers, at least, disagree with those stated in my Rubber Bible. There are probably some unstated assumptions. 121a0012 21:38, 24 June 2007 (UTC)

There are a few problems here. The article still has the references for each material I added a year ago, but the values have been changed. Either the references need to be removed or the values changed back to what the references show. According to WP:V the threshold for inclusion is verifiability, not truth. For now, I'll change the values shown to what is in the reference for each material. If anyone has a different value, then the reference for that needs to be added. Kevin 03:27, 11 July 2007 (UTC)

The values are still wrong. I am not sure to what purity they are referring (perhaps this should be indicated?) but the references are definitely wrong. e.g. the reference for Copper has the value 1.59*10^-8, and this is identical to the value given in my physics textbook. So, either the references need to be changed, or the values do. And ideally the purity, etc. should be explicitely stated.124.183.118.52 (talk) 01:40, 21 March 2009 (UTC)

I get 2.45 for Al, 1.56 for Cu, 1.5 for Ag, 2.04 for Au, 4.9 for W, 8.9 for Fe, 9.8 for Pt, 19 for Pb (all 10^-8), supposedly for "commercially pure" samples between 288-298K. Revised Nuffield Advanced Science Book of Data, Addison Wesley Longman Limited. Presumably it varies greatly between samples. ⇌Elektron 02:58, 1 September 2007 (UTC)

Are the differences significant from a science/engineering point of view? (note - I am neither) Kevin 04:48, 1 September 2007 (UTC)

I don't dispute any of the values/coefficients in the table, but there is an error in the note: "*The numbers in this column increase or decrease the significand portion of the resistivity. For example, at 21°C (294.15 K), the resistivity of silver is 1.65×10^−8." Either this conductivity change was calculated for a 10°C (not 1°C) temp. change and the note should reflect such, or the coefficient used in the calculation was .038 instead of the proper value of .0038. Also, I think the simple relation Δρ = α ΔT ρ where α is the coef. is more clear than the phrase about the significand portion. Clcasto (talk) 18:19, 3 January 2008 (UTC)

Missing information?

Well I find it pretty odd that this table of resistivities is so small... Can't be right...

And why is this table not incorporated?: http://en.wikipedia.org/wiki/Electrical_resistivities_of_the_elements_(data_page) It seems to provide a full chart of all resistivities of all chemical elements... Seems pretty fundamental in any resistivity chart, don't you think? ;) —Preceding unsigned comment added by 62.131.171.23 (talk) 21:04, 18 February 2008 (UTC)

Plus very suspicious value for calcium. As far I had deal with the calcite mollusc houses, calcite containing walls, calcite stone, cement, silicate brics etc calcium much containing materials them all are roughly good isolators. I suggess may be an author had criscrossed value 3E-8 with 3E+8???? Or value is given for naturally flooded carbonites deep under soil, thus the water is that agent making so strange resistance??? —Preceding unsigned comment added by 85.254.232.1 (talk) 15:43, 30 March 2009 (UTC)

It's presumably the value for pure calcium metal, which exists but is unstable and is not found in the natural world. Calcium compounds, of course, are different. That's not at all surprising...aluminum is a very good conductor but Al₂O₃ is a very good insulator, etc. --Steve (talk) 16:32, 30 March 2009 (UTC)

I updated the table for conductivity by simple calculation from the already present resistivity (no other change was made) EV1Te (talk) 08:25, 28 April 2011 (UTC)

more depth ?

well, 1.56 for copper is quite good, I don't know how the guy did it, but around room temperature (18-21°C), bulk copper of high purity (99.9999% Cu) is supposed to be around 1.7-1.8 depending on the guy doing the experiment. so you'll understand that 1.56 renders me a bit suspicious of the whole book. for a scientifical / engineering point of view, 5% variation in resistivity may be very important, and 0.1% thermical variations are important as 100°C of heat during use is not unheard of, meaning that 0.1% or 0.2% per°C means either +10% or +20% resistivity, with may change all behaviours if you need precise input/output.

I had another information to add to the resistivity article, but I don't really have the time and the know-how to put it in the main article :

basically, resistivity is intrinseque to a material, depending on its atome (atomic properties such as masse, active surface...etc) then you add modifiers :

• temperature (already stated in the article) increase the active surface of phonons
• impurities (quickly mentioned in the discussion)
• microstructure of the material (indirectly stated in the discussion) : this is essentially the grain size (interaction with grain boundaries) and the cristal phases (influence the density of phonons )
• size of the sample : interaction of the electron with the surfaces of the conductor

currently the size of both grains and sample really have impact on resistivity when the dimensions approche or are under the micrometer range, but maybe the fact should be mentionned, as well as impurity effects.

here are some articles (list is non exaustive)on what I'm saying (as I work mostly in mircoelectronics, those works deal with that subject, but more general links can maybe be found, I have some thesis reports, but mostly in french):

• Y. Adda, J.M. Dupouy et J. Philibert, Eléments de métallurgie physique, volume 2 physique du métal, p. 415. INSTN - CEN Saclay. (1987)
• Blatt, F. J. (1968). Physics of Electronic Conduction in Solids. McGraw-Hill Book Compagny.
• Mayadas, A. F. et Shatzkes, M. (1970). The conductivity of thin wires in a magnetic field. Physical review B, 1(4):1382.
• Sondheimer The mean free path of electrons in metals, Advances in Physics, vol. 50, Issue 6 September 2001 , pp.499 - 537
• Steinhogl, W., Schindler, G., Steinlesberger, G., Traving, M. et Engelhardt, M. (2005). Comprehensive study of the resistivity of copper wires with lateral dimensions of 100 nm and smaller. Journal of Applied Physics, 97(2):023706.
• Thomson, On the Theory of Electric Conduction through thin Metallic Films, J. J. (1901). Proc. Camb. Phil. Soc., 11:120.

If someone wants to inclued those informations in this page, and can't find the information or want to discuss it, write in my user page, I will connect to it a bit in the near futur. Calavente (talk) 01:22, 23 January 2008 (UTC)

Hey, in spanish wikipedia...

Resistividad de algunos materiales

Material	Resistividad (en 20°C-25ºC) (Ω·m)
Plata	1.55 x 10-8
Cobre	1.70 x 10-8
Oro	2.22 x 10-8
Aluminio	2.82 x 10-8
Wolframio	5.65 x 10-8
Níquel	6.40 x 10-8
Hierro	8.90 x 10-8
Platino	10.60 x 10-8
Estaño	11.50 x 10-8
Acero inoxidable 301	72.00 x 10-8
Grafito	60.00 x 10-8

Based on Matweb that I consider, good, for the resistivity article, we can be more accuracy in another dedicated only to the values.—Nicoguaro (talk) 14:26, 1 April 2008 (UTC)

Table sort

Is there anyway to get the table to meaningfully sort on resistivity? The current sort doesn't seem to grok scientific notation... --Belg4mit (talk) 01:54, 11 September 2008 (UTC)

Wire table - practical data

Resistance and Resistivity for Selected Common Metals[2]
  10-ga wire Resistance
               Ohms/ft	    Resistivity (10-6 ohm-cm)
 Silver        0.000944        1.629
 Copper        0.000999        1.724
 Gold	        0.00114  	2.44
 Aluminum	0.00164  	2.828
 Iridium	0.00306  	5.29
 Brass	        0.00406  	7.00
 Nickel        0.00452  	7.8
 Iron	        0.00579  	10.0
 Platinum	0.00579  	10.0
 Steel  	0.00684  	11.8
 Lead	        0.0127    	22   

This article would be more useful to the general reader if more practical data like above were added. -71.174.184.42 (talk) 00:07, 21 May 2009 (UTC)

Reference does not match

I checked the reference for copper that is listed in the table and the two numbers do not match. We should not list a reference with a different value, or even better we should list the correct value and a reference that verifies it. —Preceding unsigned comment added by 71.33.199.247 (talk) 21:19, 26 March 2010 (UTC)

I've corrected the value. Wizard191 (talk) 23:39, 28 March 2010 (UTC)

Sorting of tabular data

The "sort" option in tables doesn't seem to sort numbers, but instead sorts as strings - this makes it useless if using scientific notation or any number format that doesn't sort the same as strings. The "sort" function needs a stronger parser that can be told "These are numbers, not strings" and sort by magnitude of the number, not just as a string sort. --Wtshymanski (talk) 19:44, 10 February 2011 (UTC)

I suggest you re-post your message at the technical issues discussion board. :-) --Steve (talk) 20:33, 10 February 2011 (UTC)

Recent edits by 202.81.235.24

These edits [[3]] seem to largely consist of changing the units or resistivity from Ωm to m/S and changing numerical notation from e.g. 58×10⁶ to 58∘10⁶. The use of m/S while technically correct is virtually unheard of (at least unheard of by Google). The dot-notation for simple arithmetic multiplication is also correct, but probably less common the than the cross. These edits are clearly made in good faith, but they are very extensive; is there anything good that in them that can be saved, or should they just be reverted completely? --catslash (talk) 11:16, 21 May 2011 (UTC)

conductivity/density product

In the table concerning conductivity and density, I feel like the product of the two parameters (what is given) is not as interesting as the quotient. A designer would be interested in conductivity per unit of mass, so you'd want resistivity/density. A high value would mean lots of conduction for a given mass. I think the given values, while correct, are not useful.