# Talk:Electric potential

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Electrical potential is different from Electrical Potential Energy, but this definition doesn't tell the reader that. This is a common misconception, and I think that it would be very useful if the distinction was made clear here.f

Electrical potential is the potential energy per unit charge seems OK, please explain.--Patrick 10:55, 31 May 2004 (UTC)

## Article location

Shouldn't this redirect to Electric potential, rather than the other way around? 'Electrical potential' sounds to me like a pernicious neologism, born of people's tendency to add '-al' to the ends of words that they're unsure of. My physics text uses 'electric', and a Google test also turns out in my favor (though less than overwhelmingly). --Smack (talk) 03:49, 18 Feb 2005 (UTC)

I agree; I would prefer "electric potential" or "electrostatic potential", which is also what my books tend to use too. (Maxwell, in 1865, called in the "electric potential" too, although much of Maxwell's other terminology has fallen out of favor.) —Steven G. Johnson 02:53, Mar 11, 2005 (UTC)

## Voltage and potential

Since voltage is by definition a "potential difference", a potential must be able to be measured with no reference. How is this done?

Is it correct to think of a potential as "the voltage relative to infinity"? I mean infinite distance. - Omegatron 21:26, May 30, 2005 (UTC)

Similar question: If I have a piece of metal with one less electrons than protons (or a single atom with one less electron than protons), that object has a definite charge of +1, correct? The object's charge is an absolute quantity. Does that object have an absolute potential? Or does potential always involve a reference value? - Omegatron 00:17, May 31, 2005 (UTC)

You're trying to use a specific form of a concept (voltage) to shed light on a general form (potential). That's a foolish approach, if you ask me.
Yes, potential always requires a reference point. As the article says, potential is defined as a line integral over an open path. An open path must start somewhere, so there you have it. --Smack (talk) 04:28, 2 Jun 2005 (UTC)

Omegatron is making a valid point which Smack does not engage with. The definition given in the 1st paragraph of the main article is unsatisfactory for several reasons:

1) qt is not defined.

2)'Energy at a point' is a void concept as far as I can see. This should be replaced by 'energy of a small test charge qt at that point, relative to some other point'

3) the main point made by Omegatron refers to the reference position with respect to which the potential energy of qt at the point in question is measured. The concept of potential energy requires that this reference position should be identified, and the given definition of electric potential makes no mention of this reference position. The definition is therefore meaningless, and Omegatron is correct to draw attention to this defect. Smack's comment about a line integral is appropriate, but the definition given in the 1st paragraph makes no mention of this.

4) Personally I do not accept that the line-integral function is a definition of 'potential'; it is in fact a definition of 'potential difference' between points corresponding to the limits over which the integral is evaluated. Again, I see this as being the conceptual objection to which Omegatron refers, and it is a valid one. If you wish to talk about 'potential' in an absolute sense you must define an appropriate absolute reference point, and that is what I understand Omegatron to mean when he talks about 'relative to infinity' - a point infinitely distant from all charges.

Overall I am astonished that so many years have passed without a more serious-minded definition being given.

Andrew Smith — Preceding unsigned comment added by 82.32.48.177 (talk) 10:32, 14 December 2011 (UTC)

## emf - voltage drop - voltage difference - potential difference.

I teach technicians electronics and all the mathematical mumbo jumbo does not help them to obtain an understanding of the difference between emf, voltage drop & potential difference.

I teach that an "emf" is a source of electical energy which can motivate electrons around a circuit. Ie. it has to be an energy source of some sort either a battery or a power supply, a charged capacitor, the voltage produced accross an inductor when there is a changing magnetic field, a illuminated solar cell etc. Disconnect it and electrons stop moving and the circuit does not go. In a purely resistive circuit the current is always phase with the voltage

A "voltage drop" on the other hand is the voltage difference accross a load when a "current flows" through it. The current and voltage in a purely resistive the current and voltage are always 180 degrees out of phase.

A "voltage or potential difference" is the difference in voltage between any two points in a circuit, which could be an emf, a voltage drop because of a current or could include the voltage accross an "open circuit", through which no current flows at all"

Ie. In a wheatstone bridge, an "emf" is applied accross two arms each arm comprising of two resistors. A current flows through each arm producing voltage drops in each of the four resistors. A voltage difference, exists accross the open circuit between the centre points of the two arms (dependent on the balance in the bridge of course) whilst the current is 0.

As a result I use E in ohms law where I calculate the current from a power source and V where I calculate a voltage drop.

Lee de

Hi Lee, as a professional electical engineer it seems to me that the distinctions you make are entirely false and misconceived. There is absolutely no qualitative difference between a 'voltage drop', a 'voltage or potential difference' and an 'emf', and to suggest to your students that there is any difference is to mislead them completely. The fact that a voltmenter responds identically to these quantities should alert you to the possibility that they are precicely the same kind of thing. The effect that these quantities have on an electric charge (such as an electron) is also qualitatively identical; in a typical oscilloscope circuit, the electrodes of the cathode ray tube are usually connected to different points in a resistive potential-divider , and the so-say 'pd' has exactly the same effect on the electrons in the tube as a source of 'emf' would have. Perhaps the distinction that you are striving towards is that between a component which acts as an energy source (such as a voltaic cell, a charged capacitor, an inductor carrying a current, etc) and one which acts as a dissipator of energy such as a resistor. But even here you should be aware that components which act as sources of 'emf' (and of energy) can very easily become energy sinks with 'pd' simply by reversing the direction of the current. In an AC circuit a capacitor or inductor makes this change every cycle, and can do so in a DC circuit as well, depending on whether the component is being 'charged' or 'discharged'. From the point of view of circuit analysis the only useful distinction is that between components in which (at a particular instant) the current opposes the pd (energy being stored or dissipated in the device), and those in which the current is in the same direction as the pd (energy being delivered by the device). This distinction must be observed when drawing up the equations used in dc circuit analysis. Notice that this distinction is between electrical components, not between supposedly different types of voltage, which is an absurd notion. Andrew Smith — Preceding unsigned comment added by 82.32.48.177 (talk) 12:56, 14 December 2011 (UTC)

## when we connect a charged sphere to the ground

when we connect a charged conducting sphere to the ground , what happened to the charge on the surface since the electric potential (v) on it is zero"??? —The preceding unsigned comment was added by 213.209.187.34 (talk) 02:25, 17 December 2006 (UTC).

## Why is this so technical

cause it is electrostatics in everyday 3-d space. i agree, make a 1-d electro statics section.

Variables are not defined134.154.242.29 15:05, 9 February 2007 (UTC)

I totally agree, this page is next to useless to me, look at the first sentence
• At a point in space, the electric potential is the potential energy per unit of charge that is associated with a static (time-invariant) electric field.
That makes it even more complicated for me. Paskari (talk) 21:16, 28 August 2008 (UTC)

As a student studying just starting to study this material this article is almost impossible to even approach. There should be a discussion of EP in 1 dimension then the article can go further. —Preceding unsigned comment added by 141.213.66.73 (talk) 17:30, 17 September 2008 (UTC)

You are entirely right. I thought Wikipédia was intended to be a tool useful for as large a number of users as possible, not just to be a series of technical notes for use by higher level technicians and scientists. Ptyxs (talk) 14:32, 7 December 2013 (UTC)

## Vector?

So is it a vector? The article doesn't seem to be too explicit about it.160.227.129.254 23:07, 1 May 2007 (UTC)

The usual concept of electric potential is a scalar. It generalizes to a four-vector when you consider the effects of moving charges and relativity; one of the four dimensions is the scalar electric potential, and the other three are the vector (magnetic) potential. Dicklyon 05:14, 2 May 2007 (UTC)

Damn it. I had a test and wrongly answered it was a vector. You have failed me Wikipedia! Only kidding. But seriously, can we have that somewhere on the article? Its kind of important.Tourskin 22:20, 2 May 2007 (UTC)

It's in the article. If it's not clear enough, work on it. Dicklyon 00:19, 3 May 2007 (UTC)

## Electric potential vs electrostatic potential

Electric potential is measured in volts, while electrostatic potential [energy] is measured in joules. Why does the article say they're the same thing? Lecture 4 explains the difference (MIT OpenCourseWare). —Pengo 07:35, 31 August 2007 (UTC)

## Template:Electromagnetism vs Template:Electromagnetism2

I have thought for a while that the electromagnetism template is too long. I feel it gives a better overview of the subject if all of the main topics can be seen together. I created a new template and gave an explanation on the old template talk page, however I don't think many people are watching that page.

I have modified this article to demonstrate the new template and I would appreciate people's thoughts on it: constructive criticism, arguments for or against the change, suggestions for different layouts, etc.

To see an example of a similar template style, check out Template:Thermodynamic_equations. This example expands the sublist associated with the main topic article currently being viewed, then has a separate template for each main topic once you are viewing articles within that topic. My personal preference (at least for electromagnetism) would be to remain with just one template and expand the main topic sublist for all articles associated with that topic.--DJIndica 16:36, 6 November 2007 (UTC)

## lorentz scalar

The electric potential is not a lorentz scalar, it is compontent of the 4-vector $A_\mu$. Adiel lo (talk) 07:39, 26 May 2008 (UTC)

To further that comment. The second sentence is factually incorrect. The electric potential is indeed not a Lorentz scalar. (SeanH (talk) 23:12, 1 January 2009 (UTC))

## So Complicated

I spend most of my days on the biology articles yelling at the scientists for making the articles too complicated. Maybe I should appologize to them, because you guys are just so much worse. This article might as well have been written in a strange, obscure language. No effort has even been made to simplify the material. Paskari (talk) 21:19, 28 August 2008 (UTC)

Yes, perhaps you should apologize to editors that you've been yelling at. It would be more constructive to do some studying, and apply what you learn to making a better exposition. Wikipedia isn't done yet; it's not the ideal learning tool for everyone; if you find a better one, use it, then contribute, and wikipedia will get better. Dicklyon (talk) 05:01, 29 August 2008 (UTC)

I'm basically trying to figure out how ions moving across the cell membrane can lead to, and alter this bizarre thing called the membrane potential. No one even explains why there is a membrane potential. I wish someone could give a simple explanation such as the concentration and type of ions lead to different electric potentials. The outside solution has more sodium ions so it's more positive.... Instead they provide weird answers such as concentration gradients lead to a voltage across the membrane.Paskari (talk) 21:27, 28 August 2008 (UTC)

Think of the cell as a capacitor; the membrane separates the inside plate from the outside. The voltage across this capacitor is the membrane potential. A current into the capacitor charges it to a different voltage (potential). Ions flowing through the membrane provide that current (since ions are charged). That's all it is, a simple electrical circuit, nothing mysterious. Well, there is a little bit more to it, since when you have different concentration of some species, such as charged calcium ions, there will be a pressure difference due to statistical mechanics, too (i.e. a tendency to diffuse against the gradient); so the ion currents through the channels will go to zero when there's an equilibrium between the potential-driven drift current and the gradient-driven diffusion current. OK, you're right, it's a bit complicated. Someone should find a good source and use it to help explain it better. Dicklyon (talk) 04:47, 29 August 2008 (UTC)
Here is a good book about the equilibrium membrane potential, and the ion pump that pumps sodium ions out and potassium ions in, and thereby keeps the inside of the cell different from the outside, establishing the electrical and concentration differences that make cells (especially nerve cells) do interesting stuff. Dicklyon (talk) 04:59, 29 August 2008 (UTC)
HAH, that's funny because I actually have that book right here, and open to page 31. First off, thanks for the explanation. My point is, that no non physicists, even a word like capacitor will lose people like myself. It's like when I use words like lipid bilayer, and assume non biologists know what it means. I'll spend the bulk of my day looking at membrane potentials. I'll then post how I think it's easiest for me to understand it. Maybe it'll help the people here better explain some of the material. Paskari (talk) 11:03, 29 August 2008 (UTC)
So on page 31 of Neuroscience (Purves et. al. 2007) it says
• ...if the battery is used to make [the] compartment [with a higher K+ concentration] more negative relative to [the] compartment [with a lower K+ concentration], there will be less K+ flux because the negative potential will tend to keep K+ in [the more highly concentrated] compartment...
That's something I can understand because I can almost reach out and grab it. I think explanations such as these would make this page much more accessible to the average wikipedian. Paskari (talk) 12:44, 29 August 2008 (UTC)
On the other hand, here's one I can't picture (Neuroscience, Purves et. al. 207, p 54)
• Some of the local current generated by the action potential then flows passively down the axon...
My question is, how does current flow down an axon? Do the ions physically move? Do the positive ions attract negative ions and 'nudge' the positive ones down? Do electrons move through the solution and/or membrane? For all I know, it might be the case that god wills it =P Paskari (talk) 16:53, 29 August 2008 (UTC)

## "Voltage" and "electric potential" are different concepts (& we don't need cgs equations here)

It has been known to research scientists in some branches of science, for about 60 years, that "voltage" and "electric potential" are slightly different concepts. However, this doesn't seem to have made it into some physics textbooks yet, and there is lot of confusion on this issue around. I hope no-one is going to mind, but I have removed from this article all technically inappropriate references to voltage, so that this article really does become an article on electric potential (sometimes called electrostatic potential). At the time of writing, there is a modern electron-based definition of "voltage difference" in the article on "voltage". (You can start by defining "voltage difference" to be what you measure with a voltmeter, and then ask what scientific quantity it is that you are actually measuring. Quite often it is NOT electric potential difference.) At the time of writing, there is fuller discussion of the issues in the articles on "electrochemical potential" and "Fermi level", and related links and discussion pages..

I have also removed the equations that were formulated in one of the cgs systems of equations. There was international agreement nearly 40 years ago to gradually discontinue these systems of equations, and to concentrate on the single system now used for teaching in most universities. Most current students (and, I suspect, many lecturers) do not understand that there are several possible systems of equations, and most people do not need to understand anything other than the system currently used [i.e., the (rationalized) metre-kilogramme-second-ampere system that forms the basis for SI units]. If you are one of the few that do, then you will find it easier to look this up in a well-written article elsewhere. In my experience, nowadays it simply generates confusion if we try to explain basic concepts using a near-obsolete and disused equation system. (RGForbes (talk) 19:52, 10 April 2009 (UTC)) Richard

## electric potential difference

'Electric potential difference' redirects here, but nowhere in this article does the words 'electric potential difference' occur. —Preceding unsigned comment added by Loldrup2 (talkcontribs) 21:44, 25 May 2009 (UTC)

## First sentence grammer appears incorrect

The first sentence appears to have incorrect and cumbersome grammer. Presumably the charge discused is singular and the sentence becomes cumbersome without modification- suggesting more than one possible meaning to the reader.

## Vector potential of Newton

Nabla A-vec(r-vec,t)=-mu*J-vec(r-vec,t) sry, dont know how to write this properly. A-vec and the rest indicates a vector. mu = permeability of vacuum. Maybe we should ad this as well as a definition of electric potential. —Preceding unsigned comment added by 134.184.101.26 (talk) 20:22, 5 October 2010 (UTC)

## Propose deleting animations

I find the animations are so confusing as to be completely useless. I just have no idea what's going on. It doesn't help that the text and equations are mostly unreadable, and that the captions contain no further explanation. But even if those could be fixed, the bigger problem is, they seem to be videos captured directly from applets, constructed to be played with rather than constructed to clearly visually explain an otherwise-confusing pedagogical point. Therefore I propose deleting all three animations (see now-current version of the article). What do other people think? --Steve (talk) 13:59, 9 August 2011 (UTC)

These animations have multiple issues that need to be resolved. Unless the issues are resolved, they should be removed.--LaoChen (talk)00:54, 11 August 2011 (UTC)

## Finite vs. infinitesimal charges

It seems that the electric potential is "the amount of electric potential energy" per unit charge but only for an infinitesimal charge. Often if I place a finite charge Q in some location, then the charges in nearby materials (dielectrics, conductors, etc.) will reconfigure and the electric potential will change, in a way that depends on the amount Q. In those cases the change in electric potential energy is not strictly linear in Q. I'm referring here to image charge potentials and such related things. It could be clarified by saying:

• placing a unitary charge but without moving any other charges, i.e., placing the unitary charge in that location only for an instant, or
• electric potential energy per unit charge, for an infinitesimal charge.

--Nanite (talk) 07:18, 17 July 2013 (UTC)