From Wikipedia, the free encyclopedia
Jump to: navigation, search
WikiProject Physics (Rated Start-class, High-importance)
WikiProject icon This article is within the scope of WikiProject Physics, a collaborative effort to improve the coverage of Physics on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.
Start-Class article Start  This article has been rated as Start-Class on the project's quality scale.
 High  This article has been rated as High-importance on the project's importance scale.
WikiProject Measurement (Rated Start-class, Top-importance)
WikiProject icon This article is within the scope of WikiProject Measurement, a collaborative effort to improve the coverage of Measurement on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.
Start-Class article Start  This article has been rated as Start-Class on the project's quality scale.
Checklist icon
 Top  This article has been rated as Top-importance on the project's importance scale.
Wikipedia Version 1.0 Editorial Team / Vital (Rated Start-class)
WikiProject icon This article has been reviewed by the Version 1.0 Editorial Team.
Start-Class article Start  This article has been rated as Start-Class on the quality scale.
Checklist icon
 ???  This article has not yet received a rating on the importance scale.
Note icon
This article is Uncategorized.
Taskforce icon
This article is a vital article.

Siemens and Mho as reciprocals to resistance[edit]

I edited the mho reference to state that mho is used in addition to the SI unit of Siemens. Mho has not fallen out of use in all fields, especially electrical engineering. Nicholas SL Smithchatter 02:38, 19 October 2009 (UTC)


Shouldn't R = V/I be in it somewhere? In that simple form.

Ohm’s law[edit]

What about Ohm's law should that be mentioned? —Preceding unsigned comment added by (talk) 16:32, 8 November 2008 (UTC)

ohm symbol[edit]

do we really need three ohm different characters? PeregrineAY 02:34, 2005 Apr 6 (UTC)

No, but we need the right one. Unless the two sets of comments confused me, it looked like you kept the incorrect one to display. I left the comment for future editors, but rearranged to just one. There is probably no difference between using the first listed; they should both map to the same character. Gene Nygaard 04:00, 6 Apr 2005 (UTC)
Is there such thing as a "right" one? I am wondering if all users can see &*omega; and if the other ones, 937 and 8486, would be better for all wikipedians to use. PeregrineAY 07:50, 2005 Apr 6 (UTC)
There is such a thing as a wrong one. #8486 or #x2126 is the Unicode character is in a group of characters whose only purpose is to enable accurate rendition in Unicode of text originally formatted in a certain few code pages in a certain few Asian languages. It is not for use in new writing in any language, and certainly not in English.
There have been times when some browsers will support a named character and not support it numerical equivalent, or vice versa. I don't think that is a problem at all in regards to the basic Greek characters, though it still does matter for some other more obscure characters. I don't think it makes any difference if you use ω or Ω or &#x3A9 as they should all show up as exactly the same character. Here they are, side by side--increase the text size in your browser and compare them: ΩΩΩ
This way, if anybody's browser doesn't show all three of them, and all the same, they can let us know. Gene Nygaard 13:01, 6 Apr 2005 (UTC)
out of interest do you know what encoding lead to omega and ohm sign being seperated? Plugwash 01:43, 9 August 2005 (UTC)
The appearance should depend on the font specified, for example, I may have installed a general unicode font as well as a font only for Greek letter with higher priority. According to, Ω is defined as U+03A9, while ohm is another Unicode character. I noticed this when I'm using a special math fonts for Omega but not ohm. In my option, only &937 is correct, not the other two. Coolwanglu (talk) 15:36, 8 August 2012 (UTC)

Seems to me that most communication, computer and scientific systems are still restricted to ASCII for the forseeable future and in those the common notation for the ohm unit is to use the capital letter R or Z (also used for Impedance generally). This is obvious general knowledge to anyone working in any technical field but shouldn't he article mention this? Anyone know where to find citation for this ? (other than me :P ) --Miikka Raninen (talk) 07:19, 31 January 2012 (UTC)

I had a quick look in some of my books and two (Electronics Toolkit and Practical Electronics Handbook) mentioned BS 1852, which has the codes like 4R7, 470R, 4K7, etc. The books say that the decimal point is replaced to avoid it being lost on poor drawings and photocopies, and that R is used because omega is less available on computer printers. I wouldn’t say it’s specifically because of ASCII though. Also I’ve never seen it directly substituted for the omega symbol in conjunction with an SI prefix (4.7 kR, 4.7 MR), nor have I ever seen Z used as a unit (only as a quantity, traditionally italic Z). Vadmium (talk, contribs) 11:05, 31 January 2012 (UTC).

Kilohm or kiloohms[edit]

I have edited this part on the basis of the following

Google                       hits   (august 2005)
kilohm OR kilohms                 12,300   23,800
kiloohm OR kiloohms                7,180    8,440
"kilo-ohm" OR "kilo-ohms"                  10,900
"kilo-ohm"                         6,350
"kilo-ohms"                        5,470
megaohm OR megaohms               22,600   23,200
megohm OR megohms                 92,900   99,800
"mega-ohm" OR "mega-ohms"                  11,600
gigaohm OR gigaohms                7,680    7,490
gigohm OR gigohms                  1,250      853
"giga-ohm" OR "giga-ohms"                     849
teraohm OR teraohms                1,350      693
terohm OR terohms                     40       55

Gene Nygaard 05:43, 18 Dec 2004 (UTC) Urhixidur 00:23, 2005 August 22 (UTC) (for the August 2005 counts)

"The simplified spelling kilohm is approved by the Institute of Electrical and (IEEE)" - Can we have a link to that?
Urhixidur 17:45, 2005 August 21 (UTC)
Yes - section 9.3 on this NIST page cites SI 10-2002 IEEE/ASTM Standard for Use of the International System of Units (SI) as saying that "there are three cases in which the final vowel of an SI prefix is commonly omitted: megohm (not megaohm), kilohm (not kiloohm), and hectare (not hectoare)." JohnCD (talk) 21:17, 8 June 2009 (UTC)
Perfect! The above citation is relevant and yields relevant information.
Editing based data from search engine results is original research and unless it is cited from within the content of a reliable published source, it is against Wikipedia:No_original_research. Linking to sources talking about linguistics or approved spellings is acceptable, but unless a source comments on the frequency, history, or correctness of a spelling, it is an inappropriate topic for this article. Nicholas SL Smithchatter 03:02, 19 October 2009 (UTC)

The following discussion is an archived debate of the proposal. Please do not modify it. Subsequent comments should be made in a new section on the talk page. No further edits should be made to this section.

The result of the debate was move back, of course. —Nightstallion (?) Seen this already? 19:53, 26 March 2006 (UTC)

Requested move[edit]

Seems like a clear case of primary topic disambiguation. --SPUI (talk - don't use sorted stub templates!) 03:25, 21 March 2006 (UTC)

  • (Against) I'm not too sure, it seems that Ohm could be used (as last names commonly are) by someone looking for Georg Ohm or Martin Ohm. --tonsofpcs (Talk) 03:29, 21 March 2006 (UTC)
  • Neutral, I don't really care, but in any case, I fixed all the links that are clearly intended as referring to the unit from "[[Ohm]]" to "[[Ohm (unit)]]" and they need not be changed back regardless of the result, as single redirects are not a problem. — Mar. 21, '06 [04:20] <freakofnurxture|talk>
  • Oppose -- it was just moved, so there's not consensus. "Where there is no such consensus, there is no primary topic page." And it's a lot easier to find and fix links to a Generic Topic page. --William Allen Simpson 09:32, 23 March 2006 (UTC)
  • Support per below. Femto 13:30, 23 March 2006 (UTC)
  • Support. Absent consensus for the move, the article "just moved" ought to have the move undone, and agree with the points below. Lack of consensus for the move that was done means the long-standing and proper way of doing it should remain; editors shouldn't be allowed to shift the burden of proof by jumping in and making a move without consensus. Gene Nygaard 14:27, 23 March 2006 (UTC)
  • Support. I am open to the debate and I am reading the comments with interest. But for now, I see no reason for treating it differently from other unit articles (and there is still some room for consistency improvements with unit articles). bobblewik 17:23, 24 March 2006 (UTC)
  • Support. Pretty sure the unit is the primary topic here. Plugwash 17:28, 24 March 2006 (UTC)
  • Support Cacycle 18:42, 24 March 2006 (UTC)
  • Absolutely support and am shaking my head that this was moved, there is no other meaning for Ohm. I never refer to nor have I ever seen a reference to Georg Ohm or Martin Ohm as just "Ohm" (like Cher). "Ohm" means the unit, period. The only time I see George Ohm referred to as just Ohm is in Ohm's law because there are no other laws by a dude named Ohm. Cburnett 22:43, 24 March 2006 (UTC)
  • Support as per Cburnett — Omegatron 23:35, 24 March 2006 (UTC)


Ohm was in line with Becquerel, Celsius, Coulomb, Farad, Hertz, Joule, Newton, Pascal, Sievert, Volt, Watt, which are all primary topics about the unit. Gray redirects to Grey with the color as the primary topic. Henry, Weber, Siemens also have notable other uses and are disambiguation pages. Tesla redirects to Nikola Tesla. — Articles about people are available under their proper names. Someone looking for Georg or Martin will find them just as well through a dablink. Disambiguation on last names is a navigational help, not a criterion to decide whether a topic is primary. There are no other notable things called "Ohm"! (*)

(*) There is an obsolete German liquid measure called Ohm, thus Ohm (unit) itself is ambiguous, by the way.

There wasn't consensus either to move Ohm to Ohm (unit), was there? What is this move all about? As to the consensus argument, I think "no such consensus" does not mean that primary topic disambiguations may be overturned by any possible minority. There are Fiona Apple and Charlie Apple: does Apple have to be moved to Apple (fruit)? Femto 13:30, 23 March 2006 (UTC)

No consensus means that primary topics can be overturned by a minority. Most pages start as primary topics, and when they aren't anymore, they are moved (usually on the third topic, see WP:D). This has been quite fully discussed. Primary topic pages have to be so important that folks are willing to do the extra effort to find all valid and invalid links on a regular basis. That's a lot of extra work! Generic Topic pages can assume that all links need disambiguation. There's a whole project page devoted to shuffling these around. Thanks for pointing out more that need moving.
--William Allen Simpson 06:40, 24 March 2006 (UTC)
You're not going to move Apple without a discussion and a formal move request—and that's the weakest candidate in the list. Tell, what is the other meaning of "Ohm" that needs disambiguation? You misinterpret Wikipedia:Disambiguation: it can not be imposed by any minority. Consensus does not mean there can't be any opposition at all to reach it. Femto 13:30, 24 March 2006 (UTC)
The above discussion is preserved as an archive of the debate. Please do not modify it. Subsequent comments should be made in a new section on this talk page. No further edits should be made to this section.

Ohm capitalized[edit]

I've heard that the unit Ohm should be capitalized at all times since it is derived from a family name. Is that true? If not, was it ever true in the past? Binksternet (talk) 21:59, 22 May 2008 (UTC)

SI units derived named for a person should not be capitalized, but their symbols should be. Note that the symbol for the ohm (Ω) is not a Latin letter, but it is a capitalized Greek letter. --Random832 (contribs) 15:54, 19 June 2008 (UTC)
The words "Latin" and "Greek" are proper nouns, and they ARE capitalized. So are English, French, German, Spanish, etc.
Units derived from names are NOT capitalized, and neither are the named of chemical elements that are derived from proper nouns. Note: americium, berkelium, curium, einsteinium, fermium, germanium, holmium (derived from Stockholm), lawrencium, mendelevium, polonium, scandium, thorium, uranium, yttrium, and many more. Once you can get this straight, it makes it easy to remember how to do it. (talk) 01:00, 30 September 2013 (UTC)

Consumer Electronics[edit]

I was just researching ohm for my antenna strength. Not sure what 75-ohm means. After reading this article I still don't. I imagine a section about the use of ohm in consumer electronics might be a nice addition to this article. thanksDkriegls (talk) 16:15, 14 January 2009 (UTC)

Numbers on consumer electronics gear are generally dubious. In the context of radioantennas, "75 ohm" refers to the driving point characteristic impedance of the antenna - the antenna is matched when it is connected to a 75 ohm cable, which is a transmission line...oh h***, do you need to understand all this or can you just accept that you use 75 ohm cables with a 75 ohm antenna, 50 ohm cables with a 50 ohm antenna, and you might have two, four, eight, or 16 ohms speakers on your stereo? There's a frustratingly large amount of background to explain! --Wtshymanski (talk) 17:12, 29 January 2009 (UTC)
Some of the above paragraph is right, but much of it is wrong. The following is a simplified explanation. For antennas and transmission lines, what is important are the electric and magnetic fields around them, and in particular, the ratio between the electric field and the magnetic field. Electric fields work out to have the unit of volts per meter, and magnetic fields work out to have the unit of amperes per meter. Then, when you divide one by the other to find the ratio, the "per meters" cancel out. You are left with volts/ampere, and that unit is the ohm. Electrical engineers and physicists tend to refer to this as "impedance", and this is in spite of the fact that impedance is in general a complex number. In most cases, though, the impedance of a transmission line or an antenna turns out to be a real number. In other words, it is a resistance, but it isn't the kind of resistance that dissipates power by the relationship P = VI. All it is is the quotient of an electric field and a magnetic field. Transmission lines and other devices - such as antennas - work well together when they have the same "characteristic impedance" in ohms.
Also, there is no such thing as "antenna strength", and the whole terminology of "a powerful antenna" or "a powerful receiver" was made up by "science writers" who do not understand anything about electromagnetic fields in physics or anything about electrical engineering at all. Antennas and receivers DO NOT "suck in" signals, but rather they just sit there passively and get whatever electromagnetic waves hit them. Furthermore, antennas do no have any power supply, so they could not be powerful at all. Likewise, antennas, receivers, and telescopes are not "powerful", as the bad terminology says. These devices are "sensitive" in that they passively gather most of the electromagnetic waves (in the desired bandwidth) that hits them.
By the way, most people in computer science do no understand what "bandwidth" means, either. (talk) 01:35, 30 September 2013 (UTC)

Where's the HISTORY?[edit]

Start with [1]. The British Association report is on the Internet Archive, though probably too primary a source to be a good reference here. Talk about origins of the unit - starting with telegraphers, various empirical standards, the CGS "absolute" units, magnetic vs. electrostatic units, metrology, practical realizable standards, artifact standards, 20th century redefinitions, then the modern definition. Talk about the struggle to make E=IR and P=IV true by consistent definitions of volt, ohm, amp, and watt. --Wtshymanski (talk) 17:29, 29 January 2009 (UTC)

Definition section is hard to understand[edit]

I think the definition section needs to be rewritten so that it is easily understandable. After reading it five or so times, I still don't get what an ohm is. Kevin chen2003 (talk) 21:04, 20 August 2009 (UTC)

Not only that, but how hard would it be for someone to simple write "The higher the rating is in ohms the more resistance is on the line." Or is it lower? I don't know. Whatever happened to the "plumbing" analogies? -- (talk) 23:36, 28 May 2011 (UTC)
That seems to be a whole lot redundant - it's like saying "the more kilometers you have to travel, the further apart the cities are" - we have to assume the reader knows something and sometimes its difficult to draw the line. --Wtshymanski (talk) 03:04, 29 May 2011 (UTC)
"Plumbing analogies" in Ohm's Law and electricity are completely silly. The definition is that one volt across one ohm produces one ampere of electric current. Otherwise, one volt divided by one ampere is one ohm. You need to understand the definitions, and analogies are not needed.
Also, I read an article (by an electrical engineer) that claimed that electric current does not "flow". I wrote the author back with an e-mail to tell him that electric current "flowing" is standard jargon in electrical engineering, physics, and electrical technology. I told him that if he did not want to use the standard jargon, he might as well leave the field. (talk) 04:19, 30 September 2013 (UTC)


From a physics point of view I would strongly suggest to add "" to the first equation, since in this way it becomes obvious that the resistance quantum has the same units, see Conductance_quantum. —Preceding unsigned comment added by (talk) 13:43, 22 April 2010 (UTC)

Units error?[edit]

using P=I^2 * R, it seems that the Ohm should have units of ...s^-1, not ...s^-3. since [P]=J/s and [I]^2 = C^2/s, then [R] = [P]/[I]^2 = (J/s)/(C^2/s^2) = J*s/C^2 = kg*m^2/(C*s) (talk) 22:38, 13 May 2014 (UTC)

and I should add that the above section's author came to the same conclusion — Preceding unsigned comment added by (talk) 22:41, 13 May 2014 (UTC)

  • If you're referring the SI Base units, the page is correct. What Quantum was requesting is already within the page.--E8 (talk) 03:19, 14 May 2014 (UTC)

Are there Some-other Symbols for Ohm? such as ϵ , E, etc?[edit]

I'm now in a short, vocational course of electronics, and in that class, many circuit diagrams using ϵ and E for Ohm. But this was very surprising , because in Wikipedia, and any textbooks I could-not found this use, and its basis. But I found mention in several Websites such as , , , ( The last-one also tells R is also used). The first-one website also tells 4E7 = 4.7 Ohm. (That also confuses me, because we often write 4E7 = 4 X 10 ^7 ). But these websites do-not clearly mention the origin of these conventions, and do-not cite reference.

So, to improve the article, please provide further information about Symbols for Ohm, other-than capital-letter-Omega (Ω), their origins, uses etc. Thanks. RIT RAJARSHI (talk) 12:24, 7 April 2016 (UTC)

According to one of your links [2], this notation was used by the Yugoslav former electronics company Iskra and it stands for enot, meaning unit, and presumably is a Serbo-Croatian word. Thus, it is both rare in the English speaking world, and does not really mean Ohm. In principle, it could be used to mark components other than resistors. This article is not really a suitable place to discuss component marking. It is certainly not a marking system likely to be found on modern surface mount components. Those markings are discussed at Surface-mount technology#Identification. SpinningSpark 18:00, 7 April 2016 (UTC)
I agree with Spark. There is mention of this coding on the Resistor page, but manufacturers use symbols as they see fit, regardless of standardized units.--E8 (talk) 19:22, 7 April 2016 (UTC)

Assessment comment[edit]

The comment(s) below were originally left at Talk:Ohm/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.

Basic scientific style: No symbols are self-explanatory. Science has more parameters than the number of letters in the alphabet, and 'm', 's' etc. should be explained: "'m' is the distance,'s' is the time and so forth.

Last edited at 08:03, 24 November 2008 (UTC). Substituted at 01:45, 30 April 2016 (UTC)

"megohm" vs. "megaohm", "kilohm" vs. "kiloohm"[edit]

Can't we have the proper (or most common) forms listed in the article, especially as "kilohm" and "megohm" might be some of the few exceptions to the general rules (presuming it is actually "kilohm" and "megohm")?

Article Hertz has it both in the lead (kilohertz, megahertz, gigahertz, and terahertz) and in the sub section SI multiples.

OK, some of them are mentioned inside a sentence at the end of section Definition. What about a more prominent place (e.g. in the lead or a separate subsection)?

FYI: The Chicago Manual of Style has in 10.57 (16th edition, 2010):

"Note that in three cases the final vowel of an SI prefix is omitted: kΩ, kilohm (not kilohm); MΩ, megohm (not megaohm); ha, hectare (not hectoare);"

--Mortense (talk) 07:03, 22 January 2017 (UTC)

Symbol ω and Ω[edit]

About the statement in the article: "In documents printed before WWII the unit symbol often consisted of the raised lowercase omega (ω), such that 56 Ω was written as 56ω." This can be traced back to William Henry Preece in 1867. [3] He used the lowercase ω for ohm, and the capital Ω for megaohm. Ceinturion (talk) 14:22, 26 February 2017 (UTC)