Talk:Electric current

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)[reply]

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

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

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)[reply]

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)[reply]

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)[reply]

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'."

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)[reply]

50 to 150 mA may result in death, e.g. through rhabdomyolysis (muscle breakdown) and resultant acute renal failure
1-4 A causes ventricular fibrillation
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)[reply]

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)[reply]

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)[reply]

"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)[reply]

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)[reply]

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)[reply]

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

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)[reply]

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

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

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)[reply]

Vector quantity?

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