Talk:Electric current

SI

I'm adding some stuff about the SI. Electric current is a base quantity, so there isn't really a definition using other quantities. In the SI an electric current is something that just happens, electric charge is derived. So it isn't $I={\frac {Q}{t}}$, but rather the electric charge Q is defined as $Q=I\times t$. But then the official definition of the Ampere can't really be used for anything. It has infinitely long conductors with zero cross section. So I'm basically leaving the "Definition" section as "Practical Definition". I also took out the reference to ampere and coulomb there. That ($1A=1{\frac {c}{s}}$) is discussed n on the Ampere page. The second (s) was missing, anyway. Ospalh 14:52, 17 May 2007 (UTC)

I reverted your edit for the reason that the definition of electric current is distinctly different from the definition of the measure of electric current. That is, the Ampere doesn't define current just as the second doesn't define time. Alfred Centauri 15:46, 17 May 2007 (UTC)

Sources (Pun Intended)

Hi, I couldn't help noting that this page cites no sources. Granted most of it is in the domain of common knowledge, but there are a few specific statements that could use some support. Specifically under the heading "Electrical Safety", I think. GBMorris 02:07, 23 October 2006 (UTC)

I would concur. I have heard this befor that 'current' causes harm, but a citation is required. If this is true, it must have to do with the process of inducing arthymia via nerve/muscle cells, versus the energy that would heat things. I think that the references tag should be moved to this section. 64.229.8.42 (talk) 21:32, 8 October 2009 (UTC)

Request for help

Can somebody help me over at Talk:Electrodynamic tether? Somebody named Reddi (perhaps Reddi Kilowatt?) is insisting on the sentence "Although a voltage can be build up between the ends of the electrodynamic tether, current will not flow unless a open circuit exists". It seems obvious to anyone that knows electricity that "open circuits" don't carry current flow; "closed circuits" do. He is insisting that it's an open circuit because the tether has to interact with its external environment, so it's an open system; I say that it's an open system but not an open circuit. Somebody help? Rpresser 15:54, 13 April 2006 (UTC)

Hopefully the issue is resolved now... Bert 21:27, 13 April 2006 (UTC)

Thanks! Article is better, too. Rpresser 18:40, 14 April 2006 (UTC)

Error in information

The subsection titled "Electrical Safety" warns aginst electrical harm, by warning of various voltages, voltage however it not what causes harm, current, measured in amperes is, this needs to be changed urgently.

The article is not wrong. If I invite you to touch one of two conductors, one of which supplies 100 kV and the other 10 V, with unknown source impedances, which would you choose? The point is that low-impedance voltage sources are much more common in the real world than high-impedance current sources, so in general you are better off avoiding high voltages. --Heron 20:02, 31 January 2006 (UTC)

While this is true, high voltage is considered dangerous because it has the POTENTIAL to create a high current. This is proven true by Ohm's Law, which states that current is equal to voltage / resistance (I = V/R).

Lets say you put your fingers to the opposite poles of a AA battery (1.5V). A current passes through your body equal to the voltage of the battery divided by the resistance of your body (I = V/R). Needless to say, this current is negligible, since you have such a small voltage divided by a relatively large resistance. If you replace the battery with a power line supplying 40,000 volts, the current which passes through your body will equal 40,000/resistance. Now you have a large voltage and a relatively small resistance, which results in a very high, and very dangerous current.

On the other hand, sticking metal pins into your chest and connecting 5 V across them is (supposedly) a very bad thing, because of the current going through your conductive wet tissues. Maybe the article should be more specific about how both can kill. — Omegatron 03:42, 4 February 2006 (UTC)

The article makes it clear that the current is what does the damage, and that voltages are merely the sources that drive that current. I don't think we need to go into detail about weird ways to electrocute people. --Heron 10:40, 4 February 2006 (UTC)

Onve you get below the skin surface, typical point to point body resistance is about 700R. This from a BS publication (or I deduced it from there). 10mA is about the safe limit thro the heart for a reasonable time. so if V=IR, 7v looks a bit dodgy. Of course the surface resistnace of the skin is higher and probably a few kohm depending d sweatiness, tightness of grip etc. In the ELV directive any thing below 50v is deemed safe to touch. --Light current 16:31, 1 September 2006 (UTC)

Origin of Symbol

Question: why is I used as the letter for current in equations?

Answer: From the article: "Historically, the symbol for current, I, came from the German word Intensität, which means 'intensity'."

Interesting. I've often wondered about that myself. But lots of things can be "intense" — not just current. And since most early experiments with electricity were conducted by English-speaking people, why isn't the first letter of the English word used? (I know what someone's going to say: "c can't be used for current because it's the symbol for the speed of light." But then why should that be? Whose brilliant idea was it to abbreviate the speed of light as the letter c? Wouldn't "l" [the letter ell] or "s" (or perhaps "s_l") be more logical? (Or maybe the Greek letter λ [lambda]?) And "i" for current is problematic as well, because "i" (for "imaginary") is also used to signify the square root of -1, which is used frequently in electrical engineering. For this reason, in electrical engineering, the letter "j" is often used instead. Seriously, some standards organization like the IEEE or something should take a look at this and reform this bizarre system of illogical abbreviations. Just my two cents' worth. 24.6.66.193 (talk) 06:01, 29 June 2008 (UTC)

currents

--67.136.143.93 22:32, 7 Nov 2004 (UTC)Ashley D. Why is the negitive electrons going oppisite direction?

Current was originally poorly understood, like most new discoveries in science. The original + and - polarities of e.m.f. (voltage) were chosen arbitrarily, with current defined as flowing from + to -. Later the true nature of current was revealed, and showed the original choice of + and - to be back to front; in fact electrons carry charge from - to +. The flow from + to - is thus referred to as "conventional" current, because that is the convention. It makes no difference for most practical purposes exactly which way the charge is flowing, only that it does so, and that we can measure or control its magnitude. So to answer your question, why do electrons travel in the opposite direction - it's because the electron carries a packet of negative charge, so it is "attracted" to the positive terminal (opposite signs attract) - hence the flow of charge is from - to +. Graham 22:55, 12 Dec 2004 (UTC)

This subject is a favorite of mine since this question comes up all the time. I've read many an explanation that, IMHO, did not effectively answer the question. In general, confusion of this nature arises from the 'sloppy' use of terms or phrases. With that in mind, I'd like to offer some thoughts that I hope will help clarify this subject.

A ‘current’ of something (air, water, electric charge, etc.) is the flow (transport) of that something. Thus, an ‘electric’ current is the flow of electric charge. It follows that an ‘electron’ current is the flow of electrons. Since all electrons carry electric charge, an ‘electron’ current is necessarily an ‘electric’ current. However (and very importantly), an ‘electric’ current is not necessarily an ‘electron’ current. An ‘electric’ current results from the flow of any electrically charged particle including protons and ions. If there were only one type of electric charge, this distinction would be academic. But, as we all know, electric charge comes in two flavors, positive and negative, making this distinction fundamentally important.

Mathematically, a current is a vector quantity and thus represents a magnitude (how much) and a direction (where to). The magnitude of a vector is generally allowed to be negative. A negative magnitude is pictured as reversing the direction of the vector. For example, a car traveling north with a speed of –60mph is equivalent to the car traveling south with a speed of +60mph.

Analogously, a current of negative electric charge in a particular direction is equivalent to a current of positive electric charge in the opposite direction. Thus, if an equal amount of both positive and negative charge flow in the same direction, the net electric current is zero. On the other hand, if an equal amount of both positive and negative electric charge flow in opposite directions, the net electric current is twice as large as the separate positive and negative charge flows.

Finally, it is a matter of convention (hence the name, conventional current) as to which flavor of charge flow has a positive sign mathematically. The choice is arbitrary and there is no ‘wrong’ choice from the perspective of the mathematical consistency of the theory. However, it can be (and is) argued that, from a physical perspective, the best choice is to assume that the positive direction of charge flow is in the same direction as the flow of the most common ‘carrier of electric charge’, which, as we now know, is the electron. Of course, the choice that was made many years before the discovery of the electron requires that the mathematical sign of the electric charge carried by the electron is negative. So, much like the car traveling North at –60mph, the magnitude of the electric current due to the flow of electrons is negative. Alfred Centauri 16:11, 22 Apr 2005 (UTC)

Which way does the electricity really flow? - Omegatron 16:29, Apr 22, 2005 (UTC)

Thanks! Before writing my commentary, I visited the link above which, overall, is very good. However, the author states the following:

"We INTENTIONALLY DEFINE the electric current as being a flow of exclusively positive particles flowing in one particular direction. ".

IMHO, that statement is incorrect. It appears to imply that electron current is not an electric current. Perhaps I'm being too particular but, as I mentioned above, if we are not careful with our use of terms, confusion reigns. I believe the author should have said:

"We define an electric current to be a flow of electric charge where the direction of the electric current is, by convention, the direction of positive charge flow."

Now, it is clear that an electron current from the negative terminal of a battery to the positive terminal IS an electric current from the positive terminal to the negative terminal. Alfred Centauri 17:48, 2#

Yes, an electron current is not an electric current... if "electric current" is used in the way that nearly everyone uses the term: defining it to mean the "net current" where positive and negative flows have been added together. For example, if we have a one ampere current in a tube of salt water, or in a neon sign, then by "one ampere" we mean net current, and we don't mean the actual particle flows as they really exist. (Electrolytes and plasmas have two polarities of charge!) Or another example: use your digital meter to measure the amperes in a circuit and you get a reading of Net Current, since that's what meters measure. The true current in a conductor breaks down into two components: amperes of positive charge flow and amperes of negative charge flow. If we add them together, and if we treat them as "just plain current," then we're dealing with the concept called Net Current. This is not a strange concept, instead it's the one we always use. But we delete the word "net" and just call it "current." As with any terminology problem, we find it difficult to discuss the problem or even think about it if the words we're using are part of the problem. (One cure for this is to temporarily abandon the words "current" and "net current" and instead always say "charge flows" or "flow of charges.") So, back to the original question: is an electron current a (net) electric current? No, obviously not. An electric current requires that we add up all the charge flows and ignore the difference between positive charges and negative charges. A flow of electrons is a "true" current, an exotic and rarely-used concept: a current where the opposite polarities haven't yet been summed together, a current which ammeters cannot measure. --Wjbeaty 16:03, 1 January 2006 (UTC)

1. 50 to 150 mA may result in death, e.g. through rhabdomyolysis (muscle breakdown) and resultant acute renal failure
2. 1-4 A causes ventricular fibrillation
3. 10 A causes cardiac arrest (only at this current will a typical home fuse break the circuit)2 Apr 2005 (UTC)

Electric charge can flow both ways in a circuit. Obviously, the negative charges move one way whilst the postive charges (if there are any) move the other way. So it depends on what you define as current. Are you defining the flow of negative charge, or the flow of positive charge? --Light current 16:53, 16 September 2005 (UTC)

If you are saying that in a circuit powered by a battery current flows from positive to negative I would have to disagree. The primary charge carrier in that type of circuit is the electron. We all know in that case current will flow from negative to positive. I can accurately say that the current or NET current in that circuit will flow from negative to positive because the materials I have that tought me how to be an electrician. I do not deal with conventional current however, but what I do know is conventional current is mostly used in physics and the primary charge carriers for conventional current are positively charged ions, which will create a net current flow from positive to negative. If I was wrong and missunderstood what you were saying I appologize. And to answer Light Current's question I believe that was already answered previously. All current in a circuit is defined in net current not by positive or negative charge. Which ever charge is greater will define the direction of the current.NucPhy7 07:53, 25 April 2007 (UTC)

NucPhy7 said "All current in a circuit is defined in net current not by positive or negative charge. Which ever charge is greater will define the direction of the current". Nonsense! Positive charge flow in one direction is entirely equivalent to negative charge flow in the other direction (the negative sign in the charge cancels the negative sign in the direction!). Thus, one ampere of positive charge flow to the 'right' plus one ampere of negative charge flow to the 'left' gives a net electric current of 2 amperes. The question is: what is the direction of the net electric current? By convention, it is the direction of positive charge flow. If the electron charge had been assigned the positive sign instead of the negative, the electron flow in conductors would be in the same direction as the electric current. That doesn't mean that the convention is wrong in any way, merely inconvenient for metallic conductors and vacuum tubes. For plasmas and electrolytes, it really doesn't matter.

Only when positive and negative charge are moving in the same direction (due to some other mechanism than an electric field, e.g., diffusion or simply a moving reference frame) would you take the difference to determine the net current but, in any case, the direction of the electric current would always be in the direction of the positive charge flow even if the negative charge flow is greater than the positive charge flow - silly me - the direction of the electric current in this case is in the direction of the positive flow charge if it is greater and in the direction opposite the negative charge flow (and thus, opposite the positive charge flow too) if it is greater. Alfred Centauri 03:09, 26 April 2007 (UTC)

I appologize for the missunderstanding. I meant to say the net current is defined by which current charge is greater. Also the most common current flow is from negative to positive because the most common conductor in electrical circuits are metals and the primary charge carrier of a metal is the electron. Tell me how a negatively charged particle is going to travel from positive to negative. If you understand how electromagnestism works you would understand what I am saying. In regards to positive to negative current flow, it does exist in special circuimstances such as conventional current which, what I have already said, uses a conductor that has a primary charge carrier of a positively charged ion called a hole. Conventional current is most widely taught in physics and that is why those of you that are taking physics will say current flows from positive to negative. However physics also teaches the negative to positive flow of current, or at least my physics courses taught me both.NucPhy7 07:20, 2 May 2007 (UTC)

Electrons diffuse from positive to negative potential in standard p-n diode junctions. Oli Filth 23:34, 3 May 2007 (UTC)

Nuc, I wish you understood that your ideas on current are not standard. I know that you believe that they are but they aren't and there is a wealth of credible references that support what I've just said so you really shouldn't be using phrases like "if you understand how EM works..." etc. At any rate, we already know what we disagree on and I'm not interested in changing your mind so let's leave it at that. One last question for you though: What other currents are associated with a current of electrons? Alfred Centauri 00:30, 4 May 2007 (UTC)

I appears from this conversation (and my knowledge) that polarity of current flow depends largely on the medium. This clarification should be described in the article. Earlier in the article, current flow in a metal conductor is described in the electron flow direction. The conventional current flow is worded in a way that disregards the previous explaination. This discussion, if it does anything illustrates that controversy exists. The very existance of the controversy demands that the controversy appear in the article.DarthAlbin (talk) 13:52, 19 July 2008 (UTC)

Canada?

The article says the original definition of current does not stand in Canada? Are physics different up there? Maybe it's like toilets spinning backward in Australia? Kaz 00:17, 8 Feb 2005 (UTC)

Can someone back this up? I cite this as evidence that conventional current is used: http://www.control.toronto.edu/courses/110/solu.summ.2001/quiz3.may29.pdf

I removed "(Notably, this is not the case in Canada)." until someone can verify it. - Omegatron 03:44, Mar 4, 2005 (UTC)

Accidental reversion

I accidentally reverted this page by editing an out of date version. Apologies to all concerned .I hope it can be put back. Sorry!!--Light current 00:17, 16 September 2005 (UTC)

Lethal Current

According to the electrical safety section, it takes 1-4 amperes of current to throw the heart muscle out of sync. I thought that the lethal current across the heart was in the milliamperes, not amperes. 1-4A is a lot of current, if I remember correctly... --Orborde 06:03, 30 September 2005 (UTC)

It is in the milliamperes. I know what you are referring to and it does not make sense. However, I have seen many references that state death can be caused from 0.015 amps up to .09 amps. So I am not sure which is correct but I like to believe my career development course material on aircraft electrical and environmental systems that states it only takes as little as 0.015 amps to stop your heart. NucPhy7 —Preceding unsigned comment added by 132.62.88.94 (talk) 10:49, 10 March 2009 (UTC)

"Religious War", positive vs negative flow

A small fight erupts in the "currents" section above, and in many other places in literature and on WWW, because a significant portion of electronics students have been taught that all electric currents are flows of negative charge. Further, the same students were also taught that the physics standard called Conventional Current is a mistake. Yet an even greater number of students were not taught these things. And so a "religious war" exists where one side insists that the REAL direction of current should follow the negative charges, while the other side insists that the direction of current follows the positive flow. (In general, physicists and engineers use the positive convention, while technicians use the negative.) Arguments between the two sides tend to become heated and irrational. In my opinion the fight is caused by people who are intolerant of alternate explanations: people who believe that only one viewpoint can ever be correct, and that any other viewpoint is a mistake made by inferior minds; a mistake which must be actively stamped out. Yet in reality we are dealing with mental models and physical explanations... and electric circuits can be explained in many different (yet accurate) ways. In other words... if both sides of the fight are claiming absolute correctness, then both sides are wrong. If we describe electric circuits in terms of actual particle flows, then we must abandon "electron current" as well as "conventional current." We no longer think in terms of net current. Instead we always break all currents down into their component flows of various types of charge carriers. But neither side of the "war" is doing this, so neither side can claim to be following reality. Yet this is exactly the function of "conventional current." It masks the true complexity of charge flows within conductors, and instead replaces it with the simplifying assumption that all charge carriers are positive. --Wjbeaty 15:42, 1 January 2006 (UTC)

Well, I haven't looked at this page since I added my initial response to the question, and re-read all the various responses just now. I don't see a "fight" at all, just a healthy and interesting discussion, in the spirit of establishing the truth, whatever that may be. I agree with what you're saying about different viewpoints, but as far as I can see, no-one is taking a position of "i'm right, and the other view is wrong" in the above. There are some different explanations, is all.Graham 00:11, 1 February 2006 (UTC)

Check this out | Current Flow

basically Conventional Current follows electron 'holes' (positive flow) while Electron Flow follows negative electrons (go figure). Holes come out of the positive terminal on a battery and electrons come out the negative. The reason both are used is because of history mainly, industry and education has become quite reliant on Conventional Current, designing symbols (diodes) and such based on it... to change would be quite bothersome. That being said, my college course teaches us both concepts, with the opinion that neither is wrong, simply different ways of looking at the same thing.

In fact, "electron current" is wrong on two counts. First, current is not composed of electrons. Only in metals is an electric current exclusively a flow of electrons. In electrolytes no electrons flow. Currents in electrolytes are entirely composed of populations of positive and negative ions which move in opposite directions. Electrolyte conductors include batteries, electroplating tanks, the ground, your body, the oceans, etc. There are even some electrolytes in fuel cells where only protons flow. "Electron current" is wrong for another reason: it is an attempt to redefine a convention which is the basis of all physics and engineering. For example, the conventional directions of e-field, b-field, and electric current are part of Maxwell's equations. If a group of technicians wishes to alter the signs in Maxwell's equations in an attempt to make explanations of tube-type circuitry less confusing, something is very wrong. Changing the conventional current is really no less major than attempting to rename the polarity of electrons and protons. --Wjbeaty 01:51, 21 September 2006 (UTC)

Wjbeaty. I would have to disagree with you that engineers use the postive convention even though I know you are an engineer or at least on your way to becoming one. I am an eletrical technician and all the engineers I have worked with use the negative convention. I even have a physics book that states the same thing. Also there should not be a war about who is right and who is wrong because both are right. As an electrician I was only taught the negative convention because that is all I deal with. Physics teaches both but stresses the positve more. However, what is taught does not matter because both conditions exist. Conventional current is the flow of charge carriers called holes which are positively charged ions, thus creating a current flow from positive to negative. The primary charge carrier for electric current in metals is the electron which creates a negative to positive flow of current. That is why technicians and engineers will say current flows from negative to positive and physics students will say positive to negative. Being and electrician and a physics student I know both are correct. NucPhy7 08:05, 25 April 2007 (UTC)

NucPhy7, you said: "Conventional current is the flow of charge carriers called holes which are positively charged ions, thus creating a current flow from positive to negative. The primary charge carrier for electric current in metals is the electron which creates a negative to positive flow of current." This is just plain wrong. IMO, you are confused over the difference between electric current and particle currents such as an electron current or an ion current . A current is, by definition, a flow. An electric current is a flow of electric charge in the direction of the positive charge flow. Note that this definition does not refer to ions or electrons or to any other carrier but simply to electric charge only!

An electron current is a flow of electrons. Because electrons carry electric charge, an electron current is necessarily an electric current. However, because the electric charge is negative, the direction of the electron current is opposite that of the electric current. This reversal of direction is no different mathematically than specifying a velocity as "-60mph West". This is, of course, the same as a velocity of "60mph East".

To summarize: (1) Conventional (electric) current is not defined as the flow of just positive charge. It is defined as the flow of charge (of either flavor) where the direction of the current is, by convention, the direction of positive charge flow. (2) The direction of electron current is, because of the negative sign in the charge of the electron, opposite that of the electric current.

BTW, I've been an EE for a long time (and before that, a technician for 10 years) and frankly, I've yet to meet an EE that uses the negative convention. I'm not disputing your claim here, just giving you a data point. Alfred Centauri 13:34, 25 April 2007 (UTC)

Ok Centauri I don't know where you learned to be EE but my EE training taught me the the negative to positive convention. I even have the CDC's to prove it and so should you if you are EE in the air force. If you are and do have your CDC's check volume three the section after Kirchoff's law about finding current, charge, or voltage in parallel and series circuits and read the paragraph on current and you will see that you are wrong. Ask any other electrical technician, or even look it up in a valid encyclopedia, and I guarantee that you find more electrical technicians and encyclopedias will claim the negative to positive current flow, encyclopedias will most often teach both. However, I am not saying the negative to positive is the only current flow allowed by nature. If you read my entire paragraph above you would know that. If you really are EE and you really beleive you are right I don't know how you made it past tech school or even you CDC's. I don't know how long you've been EE but I have been EE for four years and I read a lot of informational books on physics and I can think of two of them that also teach the negative to positive convention along with the positive to negative convention. Electric current is particle current if you had done your homework you would know that the definition of electric current is any movement of CHARGE CARRIERS such as subatomic particles in which case they can be electrons, holes, protons, etc. And no you are the one that is confused. You are confusing the definitions of electric current with direct or alternating current. Only direct and alnternating current are defined as the flow of electric charge and they are only types of electric current. Ignorance is the mother of misinformation. If you don't believe me look up the definition of electrical current and you will see who is right. By the way I do not intend to sound condescending I am just being passionate about the subject so I appologize for my vulgar wrighting. I just don't understand why people can't look up this information from creddible sources, not Wikipedia, and they would all know current can flow in both directions depending on what conductor is used. NucPhy7 07:31, 2 May 2007 (UTC)

I 'learned' EE at the Georgia Institute of Technology where I currently teach EE classes whilst doing research on my Ph.D. Here's a question for you: how many references will I need to quote before you see that what you wrote above is confused? Here's one from the first book I picked from my book shelf:

"Suppose that an amount of charge dq flows past some given point of the wire, in a time dt; then the electric current is defined as charge divided by the time... For the sake of mathematical uniformity, whenever we need to indicate the direction of the current along a conductor, we will follow the convention that the current has the direction of a hypothetical positive flow of charge." [1] Alfred Centauri 13:50, 2 May 2007 (UTC)

You understand that your statement uses the words SUPPOSE, HYPOTHETICAL, and the phrase FOR MATHEMATICAL UNIFORMITY don't you? Those are not definitions those are directions to follow in order to solve an equation. From wrighting that, you have just dealt yourself a blow by using a hypothetical flow of charge and variables that are created for mathematical uniformity. You have to think outside of the box. I have schooling and experience as an Aircraft Elictrical and Environmental Systems Journeyman. I was only taught the negative to positive convention. However, because I am no longer in school I have become open minded and did research in fields other than my own, and found out that my books were being biased, as I'm sure yours are too. How about you compare the definitions, use materials other than you text books, of conventional current and electrical current and you will see that they are opposite in regards to current flow. The fact that you're in school makes you bias towards what you are taught. I can counter your resources with resources of my own. Again look up the definitions. How bout I just cite them. "Current: A flow of electric charge through a conductor. The current at a particular cross section is the rate of flow of charge. The charge may be carried by electrons, ions, or positive holes." so you see charge carriers determine the direction of current flow. "Conventional Current: A 19th-century convention, still in use, that treats any electrical current as a flow of positive charge from a region of positive potential to one of negative potential. The real motion, however, in the case of electrons flowing through a metal conductor, is in the opposite direction, from negative to positive. In semiconductors hole conduction is in the direction of the conventional current, from positive to negative; electron conduction is in the opposite direction, from negative to positive". Those definitions are from the Oxford Dictionary of Physics. So you see conventional current is used to TREAT any current as flowing from positive to negative but the definition then explains some charge carriers that are needed to actually create current flow in either direction. So to clear this up you were right, current is a flow of electric charge but we were both wrong thinking that electric current is different from partical current. There is no such thing as partical current. Charge is a characterisic of particles, and in regards to current flow, particles are the charge carriers, so it can not be said that current is the flow of charges and not particles when they are the same thing. BTW as you can tell I enjoy debating and, even though it may be hard to tell, I am in no way trying to degrade your schooling. Or am I in any way trying to claim I know more than you. I am simply trying to get to the bottom of this and if you turn out to be right I will gladdly concede. As you may infer I enjoy hearing both sides and take both into consideration, hence why I enjoy debate.NucPhy7 16:33, 2 May 2007 (UTC)

You quoted the following """Current: A flow of electric charge through a conductor. The current at a particular cross section is the rate of flow of charge. The charge may be carried by electrons, ions, or positive holes."". I agree with the author of these words. Then you said: "so you see charge carriers determine the direction of current flow". I don't agree with that and further, I don't see how the citation you give even addresses the direction of current, much less supports your assertion.

This is, I believe, our fundamental disagreement. There is really no need to discuss anything else you've mentioned above regarding this because we now know exactly what we disagree on.

With your interesting interpretation of the citation I gave above, I'm doubtful that providing your with another citation from a semiconductor physics textbook that contradicts your statement above is going to cause you to question your position on this but that's OK with me. While I too enjoy a good debate, this one is no longer interesting to me for the reason that we've found exactly what it is we disagree on and that's that. That is, let's agree to disagree on this and leave it at that. Regards, Alfred Centauri 02:06, 3 May 2007 (UTC)

You make a good point, however, the definition of conventional current gives examples of charge carriers that cause current to flow positive to negative or from negative to positive. And it states that the real motion of current in which case is carried by electrons flows from negative to positive and states that holes will cause current to flow from positive to negative. The definition of current was not as complete as I would have liked it to be but it was the most credible source I had available to me, and it implies that charge carriers determine the direction of current flow. I agree with everything you have said in regards to positive to negative current flow, I am simply trying to make you aware that current most often in metal conductors, not semidconductors, flows from negative to positive. Semiconductors use hole charge carriers so therefore you will have a positive to negative flow of current. NucPhy7 07:35, 3 May 2007 (UTC)

Nuc, I don't need to be made aware that in a metallic conductor, electrons move in the direction from - to +. Our disagreement is this: I say that electrons moving from - to + is an electric current from + to -. You say that electrons moving from - to + is an electric current from - to +. This is our disagreement, correct? Alfred Centauri 13:32, 3 May 2007 (UTC)

I'm with Alfred on this one. The standard (conventional) definition of electric current is always in the direction of the equivalent flow of positive charge. This is abundantly clear from the existence of a standard unit of electric current, the ampere, which has a polarity indicating the direction. One coulomb/second of positive ions moving left-to-right is denoted as +1A from left-to-right, as is one (-)coulomb/second of negative ions moving right-to-left. The direction of the "+1A" does not alter.

If instead we were to re-define current in terms of the direction of the charge particles, as you have done for electrons in a wire, then not only would it become difficult to define what we mean by "+1A", but furthermore, where would this definition get us when there are both +ve and -ve charges flowing, as there are in (for instance) bipolar transistors and ionised solutions? Oli Filth 23:21, 3 May 2007 (UTC)

Rename to electric current?

Does anybody mind if I rename this article to "electric current"? I see from the history of "current" that this article was originally under that name "current (electricity)" was originally called "current", and then someone moved it to "current (electricity)" to make "current" a disambig page. I think the brackets look ugly. --Heron 20:13, 31 January 2006 (UTC)

Fine with me. — Omegatron 22:39, 31 January 2006 (UTC)

Thanks. I'll wait a few days in case there are any other comments. There's no rush. --Heron 21:01, 1 February 2006 (UTC)

electric current would be a better name Salsb 23:03, 1 February 2006 (UTC)

I don't see what's wrong with electric current redirecting here, but whatever. --Orborde 08:42, 3 February 2006 (UTC)

Origin of the letter I

The book Introductory Circuit Analysis (Seventh Edition) by Boylestad claims the letter I derives from the French word for current: "intensité" as it was a frenchman André Marie Ampére that first discovered it. The article however claims it derives from a German word "Intensität", any references to that? --lenko 13:40, 7 June 2006 (UTC)

Vector quantity?

Is electric current a vector quantity? —vedant (talk • contribs) 03:35, 9 July 2006 (UTC)

This [2] says no. But current density is!--Light current 16:49, 1 September 2006 (UTC)

Current density

What is the purpose of repeating the first part of the current density article in the Electric current article? treesmill 15:21, 1 September 2006 (UTC)

No real point AFAICS. Just left brief desc now--Light current 16:45, 1 September 2006 (UTC)

Add to article section on measuring current

I'm just getting started using Wik.

I wanted to find out some ways to measure small amounts of current in a microcontroler project and in 12 volt vehicle systems. I didn't see it in the contents of this article.

I'm wondering if a section on measurement would be useful to others. For example, how to connect VOM in series or how to measure a larger current with a precision resistor or the clamp-on measurers for house levels.

A section of this sort would be useful in articles on voltage and resistance as well.

Thanks for the effort & attention to accuracy you guys have put in to date.

John Kauffman

Yes I thikn a small section on current measurement would not go amiss. Do you want to start it? 8-)--Light current 19:35, 22 September 2006 (UTC)

I can try a draft, but I have never done this before and am by no means an authority on the subject. - JK

Picture

Might be useful somewhere?

Current scales

Symbol for voltage

Are we having U or V?--Light current 01:11, 13 November 2006 (UTC)

by samyak —Preceding unsigned comment added by 59.95.105.70 (talk) 09:03, 27 May 2008 (UTC)

Electrons flowing through a straight wire...(+ gravitational analog?)

I understand that if electrons are flowing through a straight wire; that this causes circular lines of magnetic field. How does an exterior electron behave? Does it stay within the perpendicular plane spiraling outward?; the circular part of the electrons motion due to the magnetic field and the 'outward' part due to electrical repulsion with the electrons in the wire? Or does it leave the perpendicular plane in an outward helical spiral? Gravitational analog: If we replace the wire with a trail of large rapidly moving masses will this induce an exterior mass to spin (and also move towards the trail of masses)? Somehow I just can't picture there being an associated field moving the exterior mass circularly around the trail. I imagine the difference in the field causing intrinsic spin in the exterior mass. So much for intuition. Does anybody know what really happens? Scot.parker 20:16, 29 October 2006 (UTC)

Problems in the 'definitions' section

There are, IMHO, problems in the definitions section of this article.

"The magnitude of an electric current at a point is defined as the time derivative of electric charge".

The electric current I (a scalar quantity) and the electric charge Q are not point functions so we cannot define I (or Q) at a point. I is the amount of electric charge crossing an oriented surface in unit time. Q is the amount of electric charge contained within a volume defined by a closed surface. If this closed surface (with outward pointing normal) is used to determine I, then we have the following:

${\frac {dQ}{dt}}+I=\$ (rate of creation of electric charge within the volume)

But, since (net) electric charge does not appear to be created or destroyed, we have:

${\frac {dQ}{dt}}+I=0$

This is a mathematical statement of conservation of electric charge. Thus, it is because of the conservation of electric charge that we can say that I equals the (negative) time rate of change of charge but, once again, this doesn't define electric current.

The point form of this equation is:

${\frac {d\rho _{e}}{dt}}+\nabla \cdot {\vec {J}}_{e}=0$

So we can say that the strength of the source of electric current density at a point equals the (negative) time derivative of the electric charge density at that point. But, such a statement is likely to baffle most readers of this article.

So, I have changed the definitions section to read:

The amount of electric current (measure in amperes) through some surface, e.g., a section through a copper conductor, is defined as the amount of electric charge (measured in coulombs) flowing through that surface over time. If Q is the amount of charge that passed through the surface in the time T, then the average current I is:

$I={\frac {Q}{T}}$

My making the measurement time T shrink to zero, we get the instantaneous current i(t) as:

$i(t)={\frac {dQ}{dt}}$

I do believe the above gives better 'picture' of current (visualize electrons pass through a cross section of wire) and gives justification for why i = dQ/dt without all the overhead. Alfred Centauri 21:21, 20 March 2007 (UTC)

cathode/anode incorrectly labelled?

Contrary to the galvanic cell picture in the article showing the cathode as the electron/ion receiving lead of the circuit, I was under the impression that regardless of the nomenclature convention used to define current flow direction, the cathode is defined as the electron/ion doning lead and the anode as the electron/ion receiving lead. Please correct me if I am in error. (It is worth mentioning the example of the Cathode Ray Tube which is an example involving electrons.) —The preceding unsigned comment was added by Nargibay (talk • contribs) 01:46, 27 April 2007 (UTC).

You have it backwards. The cathode is where the electrons go in. With the cathode ray tube, you have to feed electrons into the cathode to replace the ones that it emits into the internal vacuum. In the galvanic cell, cations (+) from the electrolyte go to the cathode, making it positive, so it attracts electrons inwards from the external circuit. --Heron 17:36, 27 April 2007 (UTC)

Current Velocity

If it is true that information is transported by an electric current with the speed of light as suggested by the article, why was there this large delay for phone calls to the other side of the globe in former times, when copper cables instead of fibre optics and satellite links were used? --Mudd1 09:29, 25 August 2007 (U

It was because they needed to pause to allow clarity between the distorted wave forms. (Nurse Hilditch 16:25, 1 October 2007 (UTC))

b —Preceding unsigned comment added by 150.104.25.87 (talk) 16:22, 18 October 2007 (UTC)

Speed of energy transmission

Oli Filth, you seem to be under the impression that electrical energy propagates at 'close to the speed of light' in electrical cables and you repeatedly and wrongly revert any correction to this error. In your latest reversion you refer to the Velocity of propagation article in which the only cable type listed which achieves 95% of light speed is ladder line. This is to be expected because the reason for the reduction of propagation speed is the presence of material with a dielectric constant greater than one around and between the conductors. This effect is reduced in ladder line because the only material around the conductor is a thin layer of insulating material sufficient for mechanical location of the conductors in relation to one another, and the material between the conductors is pierced at regular intervals to give the ladder effect. This minimises the dielectric constant in the vicinity of the conductors. Even this only achieves 95% of light speed. The vast majority of electrical cables, in particular those used for power distribution, are not concerned with this and make no attempt to reduce the dielectric constant of the insulator. None of these will achieve anything close to light speed. The only power distribution cables where this is not the case are overhead transmission lines which rely on air for insulation, but these are a minority of power distribution mileage. I have made the necessary corrections. treesmill 15:32, 14 November 2007 (UTC)

By "close", my intended meaning was the standard engineering use, i.e. "within an order of magnitude", i.e. not, for example, in the region of 10km/h, or 10km/s, but in the region of 10^8 m/s. The "typically 50 to 75%, except for those that are higher" (to paraphrase) change that you've made bothers me; why not simplify it to something less verbose, along the lines of "a large fraction", or "50 to 95%". There's no need to go into the details of which types of cables can achieve higher in this article. Oli Filth^(talk) 17:51, 14 November 2007 (UTC)

I was trained as an engineer at university and afterwards and I have never heard 'close' interpreted in that way. The standard way of expressing the relation you describe in science and engineering is to call it 'of the order of'. However, Wikipedia is not an engineering manual, it is for the use of ordinary people with no necessary technical background. The use of 'close' in this context is completely misleading.

What you call a 'paraphrase' is a distortion. 'Except for those that are higher' is not a paraphrase of 'except in specially designed cables'. The latter phrase conveys to the layman why a higher figure they may have encountered might differ from the figures given. The reference to Velocity of propagation is a useful link for those who want more detailed information. treesmill 19:36, 14 November 2007 (UTC)

Sorry, let me clarify! I meant casual engineering use (in many engineering design situations, a factor of 10 is often deemed "close enough"). A factor of 50% or higher is equivalent to a discrepancy of 3dB or less. Of course, "order of magnitude" or "of the order of" would be more precise than "close", but they're also fairly specialised - if the reader isn't a scientist or engineer, it's quite likely that these aren't phrases they'll have encountered before.

You're right that Wiki isn't an engineering manual; however, on the other hand, verbosity is something we should try to avoid as well (as well as details that are outside the scope of the article). The issue I have is that it seems somewhat arbitrary to pick 75% as an upper bound, and then write everything else off as "specially designed".

Following this discussion, the way I'd phrase it would be along the lines of "The associated electromagnetic energy typically travels at a large fraction of the speed of light". By "large", I mean "above 50%"; we can make that explicit if needs be.

I entirely agree that the velocity of propagation article is a useful link (albeit a fairly spartan article). Oli Filth^(talk) 19:58, 14 November 2007 (UTC)

Conventional Current

The proper name of this convention is "conventional flow notation," not "conventional current." The name for the opposite of this is called "electron flow notation" (which is technically the correct one in terms of direction of electrons). Mdoc7 (talk) 22:21, 2 March 2008 (UTC)

"Conventional current" is overwhelmingly commonplace (46,400 Google hits) vs. "electron flow notation" (only 183 hits). Do you have anything to support the notion that "conventional current" is in some way incorrect terminology? Oli Filth^(talk) 22:29, 2 March 2008 (UTC)

Relevant page history

I have undeleted some relevant page history and moved it to Talk:Electric current/Old history. Graham87 16:56, 13 October 2008 (UTC)

Very good comprehensibility

This article is very helpful and easy to understand, especially the section Electric_current#Current_in_a_metal_wire. The basic concept of an electric current is clearly stated, I'm impressed by the amazing comprehensibility. =] WinterSpw (talk) 06:51, 14 November 2008 (UTC)

Millimetre per second?

You mean an electron "in a copper wire of cross-section 0.5 mm², carrying a current of 5 A" will take 1000 seconds to travel a meter? This is clearly wrong.--81.174.3.90 (talk) 01:27, 14 February 2009 (UTC)

I'd have to look it up but the drift velocity of an electron is a lot less than the velocity of the current. If you consider how small the voltage drop is in that length of copper cable, you can see that individual electrons (whatever *that* means) have very low kinetic energy - and so, low velocity. --Wtshymanski (talk) 02:40, 14 February 2009 (UTC)

See the article Drift velocity which needs a numerical example. --Wtshymanski (talk) 18:30, 14 February 2009 (UTC)

Introduction

I noticed some innaccuracies in the introduction. First of all, a current is not a flow of electric charge, but rather a flow of electric charges, those charges being electrons. Also, it later states that the charges moving in a current can be either electrons or ions. This is also incorrect. Electrons are the only particle moving in a current. The source sited does not once use the term "ion", much less claim ions move in an electric current —Preceding unsigned comment added by 24.199.162.154 (talk) 07:22, 1 April 2009 (UTC)

• Wrong! WHICH WAY DOES THE "ELECTRICITY" REALLY FLOW?. Ions or protons can be charge carriers (conventional current), electrons can be charge carriers (electron current), ions AND electrons can be charge carriers in opposite directions in the same current (bi-directional flow). Perhaps someone needs to find a more "mainstream" source that Beatty, however, facts are facts, regardless who says them... 64.122.15.114 (talk) 19:34, 3 April 2009 (UTC)
• P-holes in semiconductor physics can also be considered "charge carriers" (counter-intuitive). Can someone please correct the erroneous statement in the intro that ONLY electrons act as charge carriers? 64.122.15.114 (talk) 19:36, 3 April 2009 (UTC)

Certainly ions can move, carrying charge; e.g. Sodium ions in solution, missing some electrons, move along with positive current. As for holes, yes, but that's really just a conceptualization of complicated electron states, so with holes, it's not really wrong to say the charge carriers are electrons moving the other way. Dicklyon (talk) 00:51, 4 April 2009 (UTC)

update

needs mor CONTENT!!!!!!!!!!

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