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According to ISO 80000-6:2008 Quantities and Units - Part 6 Electromagnetism: The name “electromotive force“ with the abbreviation EMF and the symbol E is deprecated. See IEC 60050-131, item 131-12-22.
The Emf potential of the cells active electrochemical material is the quantitative measure of the level of an opposing voltage which would stop the electrochemical material's electrons from moving. Then if that voltage is lowered, the electrons will move through through the connecting circuit in the direction of the lower voltage potential. In rechargeable cells, an increase in back potential will reverse the electrochemical process and restore the electron supplying properties of the cell's negative and positive plate materialsWFPM (talk) 19:42, 2 September 2009 (UTC)
In the introductory section, before the table of contents, there should be 1-2 sentences with language easily understood by a non-Physicist. That section could also include some disclaimer verbiage such as "approximately" or "like...". It would then go on to the more precise introduction and explanation.
I certainly respect the current wording, and that using simpler language would be imprecise. But if you're not a real techie the current introduction is hard to read.
Something like:
"EMF is an electrical property of devices like batteries and motors that is related to (similar to?) voltage. There are several different technical definitions of emf. Even the letters in the abbreviation "e m f" stand for different terms in some textbooks. And the letter "F", which usually stands for "force", doesn't mean the same thing as it usually does in Physics. Although EMF can be measured in Volts, it doesn't have the same meaning as "voltage" normally does in electronics. The actual definitions of emf are rather technical."
My example above uses lots of vague words and is imprecise, so perhaps it's not up to Wikipedia standards, so I'm posting it here instead. Since it's in the introduction, and I think it's clear that it's imprecise, wouldn't that make it OK? Or perhaps somebody can do better while still be as clear? Ttennebkram (talk) 07:27, 17 October 2009 (UTC)
The term "voltage" is introduced without definition in the lead-in, so that its relevance to emf is obscure. I lack the ability to rectify this. Myron (talk) 17:12, 19 June 2011 (UTC)
Electromotive force: The driving force which maintains the flow of current in the circuit is called Electromotive force
It is denoted by E. —Preceding unsigned comment added by 202.56.7.148 (talk) 10:23, 26 March 2010 (UTC)
The definition as given is patently absurd; a voltage cannot be defined as an energy. I have changed it to the quotient of energy & charge. A more radical criticism is this: as an engineer, I have no use for emf; it does not differ in any respect from any other voltage, and to suggest that it does can only be misleading and unhelpful to beginners. When a battery is connected to a resistor, the terminal voltages of the battery and of the resistor are absolutely identical and indistinguishable. It is absurd to call one a pd and the other an emf. The fact that one component is a source of energy, and the other a sink or load is a point of distinction between a battery and a resistor - that is between the two devices. It is not a distinction between 2 voltages or types of voltage. Whether a device acts as a source or a load can be distinguished by the direction of the current with respect to the voltage, not by any examination of the voltage alone. I feel that no discussion of "emf" can be complete without these points being made. The term is actually obsolete, and should be abandoned; we wisely make no similar distinction between types of forces. A further point is that in the article the "emf" of a cell is described as its open-circuit voltage, a series equivalent circuit being assumed. But whoever wrote this neglected the fact that a parallel equivalent circuit is equally valid, in which case the open-circuit "emf" would clearly be a "pd" - that is the voltage developed across the internal conductance by the internal current generator. G4oep (talk) 13:25, 30 January 2015 (UTC)
...doesn't really make sense. Current is not defined as electrons and ions. Current is a flow of electric charge. The sentence is currently saying "that which tends to cause the flow of electrons to flow." The common saying that current "flows" is erroneous. Current does not flow. —Preceding unsigned comment added by Pseudov00 (talk • contribs) 04:57, 11 April 2010 (UTC)
The "Electromotive Force" is that which enters a persons house through his electric power line connection, and causes activity in his connected and turned on electric appliances. Its intensity value is rated in volts and results in a flow of the electric current carrying constituents of the appliances. Its power or Energy rate delivery characteristic is rated in watts (joules/second), which value is integrated over a time period to arrive at the delivered energy value in Watt hours. Note that since the advent of AC power, there is practically no entry of matter through the power line connection into the house, Just the delivery of the electrical EMF and associated electrical power and energy.WFPM (talk) 18:28, 3 November 2011 (UTC)
"For a time-varying magnetic flux linking a loop, the electric potential scalar field is not defined due to circulating electric vector field, but nevertheless an emf does work that can be measured as a virtual electric potential around that loop".
"In the case of an electrical generator, a time-varying magnetic field inside the generator creates an electric field via electromagnetic induction, which in turn creates a voltage difference between the generator terminals. Charge separation takes place within the generator, with electrons flowing away from one terminal and toward the other, until, in the open-circuit case, sufficient electric field builds up to make further movement unfavorable. Again the emf is countered by the electrical voltage due to charge separation".
In a DC machine the magnetic flux within the machine can be constant. What does "unfavourable" mean in this context ? Is not the open-circuit terminal voltage simply equal to the induced voltage ? Current does not flow because we are considering an open circuit, and not for any other reason.
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For a time-varying magnetic flux linking a loop, the electric potential scalar field is not defined due to circulating electric vector field, but nevertheless an emf does work that can be measured as a virtual electric potential around that loop.[5]
You can define a multi-valued potential for a loop of radius a using the angle:
Then the electric field is
as expected.
The following statement in the article, just above the table of emf for various cells:
"The electromotive force produced by primary (single-use) and secondary (rechargeable) cells is usually of the order of a few volts. The figures quoted below are nominal, because emf varies according to the size of the load and the state of exhaustion of the cell."
is inexplicable. The statement that emf varies with load contradicts the definition of emf, which is potential difference in open circuit, when there is no load. Of course the voltage delivered varies with load. If the internal resistance is r and external resistance is R the cell with emf E will deliver current I = E/(R + r) and the delivered voltage is V = IR = ER/(R+r). V varies with R but E does not.
The statement that E varies with the state of discharge is experimentally correct but it is not explained in the section about the source of emf. This section presents a standard and simple model which predicts that E depends on atomic properties of the atoms and ions participating in the reaction. It is by measuring E that we determine these atomic properties. How can the results depend on the state of discharge of a cell?
Bukovets (talk) 16:59, 25 July 2017 (UTC)
Should we go with the traditional lowercase emf, or all-caps EMF? An anon capped, claiming "typo", I reverted back to the conventional lowercase, and he reverted back saying that "Common usage in this case is neither correct according to any of the manuals of style nor encyclopedic." But that's not true; most style guides do use lowercase emf (and older ones e.m.f.) according to this book search. Dicklyon (talk) 01:19, 10 May 2018 (UTC)
The article provides
showing the relation between emf and the integral of E. It seems logical that there could be an equivalent/analogous relation between E and the derivative of emf. If so, can it please be added to the article.
—DIV (120.17.127.14 (talk) 09:41, 9 August 2018 (UTC))
Why is it "emf" when it is "back EMF"? (Or vice versa, why isn't it "back emf"? --Mortense (talk) 22:59, 21 July 2019 (UTC)
How come the sign in the definition of emf in a conservative electric field is different from the sign in the definition of the induced emf? 2001:1470:FF80:5:5539:D087:2C3C:17CA (talk) 09:00, 23 December 2021 (UTC)
Hi user Constant314. In the recent edit reversion you said that voltage doesn't have to be a difference. As far as I know, it does. Voltage is also called electric potential difference, not just electric potential; even Wikipedia agrees. Don't you agree? If not, what does "voltage" mean to you? Are you saying that voltage is the same as electric potential? --Alej27 (talk) 23:22, 29 January 2022 (UTC)
As has been noted in anonymous comment above, IEC/ISO has deprecated '"electromotive force" as the standardized term in favor of "source voltage" a few years ago (IEC electropedia). This should be acknowledged in the article in some way. --Jähmefyysikko (talk) 20:37, 27 February 2022 (UTC)
@Dicklyon: We have had discussions across several articles in the past. Here is part of it [1]. Unfortunately, it doesn't show the conclusion. Here are the "n-gram results" showing an overall perponderence of lower case, although recently that has reversed. Anyway the community consensus was to use lower case. So, I am reverting it back to lowercase, pending further discussion here. Constant314 (talk) 15:33, 4 April 2022 (UTC)
The first subject on this talk page says "According to ISO 80000-6:2008 Quantities and Units - Part 6 Electromagnetism: The name “electromotive force“ with the abbreviation EMF and the symbol E is deprecated. See IEC 60050-131, item 131-12-22." In which case it seems to me that this page should be renamed to whatever ISO considers the proper term, and then Electromotive force should simply be a redirect to the properly-named page. EMF isn't a force, so probably shouldn't use the word "force" in it or emF.
But what is the proper name? When I look up "ISO 80000-6:2008 Quantities and Units - Part 6 Electromagnetism" or "IEC 60050-131" online the only results I get are for a book that I have to pay hundreds of dollars for. Em3rgent0rdr (talk) 19:18, 25 September 2022 (UTC)
Intro says:
> Sometimes an analogy to water pressure is used to describe electromotive force.
But without explaining the analogy, that doesn't tell me anything useful (and actually adds confusion). When I look up the referenced citation for that (https://books.google.com/books?id=OW0SAAAAYAAJ&q=%22electromotive%20force%20is%20that%22&pg=PA172#v=snippet&q=%22electromotive%20force%20is%20that%22&f=false), I find two excerpts which do not really talk about pressure at all (but maybe there is other text outside of the excerpt that google books link provides which explains the analogy?)
My opinion is to delete that entire sentence because as it stands now it harms rather than helps understanding. Unless someone can provide a good simple clear explanation of the analogy. Em3rgent0rdr (talk) 19:28, 25 September 2022 (UTC)
Our article currently states Volta's mistake of labeling it a "force" is a misnomer that persists as a historical relic. Calling Volta "mistaken" is a bit presumptious of us especially as the cited source describes this as neither a mistake nor a misnomer. It's hardly mistaken at a time when force did not have the firm definition it has now. We wouldn't call Isaac Newton's laws of motion "mistaken" and "misnomers" even though Newton's concept of force is at odds with what we now describe as force (Newton's force is what we now call impulse). SpinningSpark 15:57, 4 November 2022 (UTC)
What does it mean when the end of a cell is + or - 105.112.190.215 (talk) 23:29, 5 March 2023 (UTC)