Talk:Electric current/Archive 3

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Archive 3

"Conventional current" is a red herring, and direction is not arbitrary

The term "conventional current" suggests two harmful and false ideas: (a) that the direction of current has been chosen only by convention and is arbitrary, and (b) that there is some other workable possibility, where current direction is assigned to be positive in the direction of particle movement (whether these are electrons, ions or whatever).

In electrical engineering, and the entire electrical and electronics industry, the plain word "current" refers to the rate-of-flow of _charge. It has the unit "amp", whose meaning and size is defined in the System Internationale.

In these disciplines, the plain word "current" is not used to refer to the flow rate of electrons or other particles that carry the charge per se. It is certainly desirable to be able to talk about the flow of particles, so terms like "electron current" are used.

In this article, we see the sentence: "The direction of conventional current is arbitrarily defined as the same direction as positive charges flow."

There is nothing arbitrary about this, and no additional "conventional current" convention involved. Current is a flow rate, defined like any other flow rate, as:

Flow rate = Amount of substance / time

The substance moves past a particular point in a particular direction. Assuming that the amount of substance is positive, and the time is positive, then this formula produces a positive flow rate in that same direction.

When the substance is electrical charge and the flow rate is electrical current, obviously current will be positive in the direction that positive charge moves. No additional convention involved.

If electrons, carrying negative morsels of charge, move in the direction A toward B, then using the same flow-rate definition (formula) it is certainly correct to describe this as a "current in the direction A to B", so long as the current value is shown as a negative value, since the electrons carry negative charge.

But as usual when discussing any phenomenon, we speak with a positive value of that phenomenon in mind. If I say I'm traveling north, listeners don't imagine that I'm traveling north with a negative velocity (ie: actually progressing south).

It's the same with current. In common discussion, when we discuss the current direction, we really mean the direction in which the current value would have a positive sign. Inevitably this must be in the direction opposite to the movement of the electrons, so in this example, "a positive current in the direction B to A".

Both of these descriptions of the current correctly describe the example, and are based on the same convention, which is only the polarity convention for charge.

The idea that there is a _workable_ alternative convention in which the term "current" is positive in the direction of electron flow, is false. Some people (including some books) do attempt to use the word "current" that way, but it is fundamentally at odds with the charge polarity of the electron, and quickly leads to algebra that doesn't work. A genuine alternative convention would instead redefine charge with opposite polarity, redefine voltage with opposite polarity and so on, otherwise the basic algebra of electricity can't be reconciled. Gwideman (talk) 06:13, 17 December 2018 (UTC)

The convention was defined before the electron was discovered. At that point, it was arbitrary, and the opposite convention would have worked just as well. Now that one convention is widely used, yes, an alternative convention isn't workable. There are, in fact, very few cases where the distinction is important. The quantum mechanics of indistinguishable particles restricts following individual electrons. As I have noted a few times, there are some metals with a positive Hall coefficient, such that holes are the majority carrier. Since more metals have a negative Hall coefficient, I suppose there would be a slight advantage to the opposite convention, but very slight. About the only case that really matters is thermionic devices, where electrons are emitted from a hot cathode. But even in this case, it is the convention doesn't really cause problems. One just remembers what the convention is. Otherwise, it is interested in simple, not consistent with quantum mechanics, models for metals where one might believe the distinction matters. It seems to me that the article explains it well enough. Gah4 (talk) 08:23, 17 December 2018 (UTC)

Gwideman, I'm not sure what your main points are with respect to the article. One point which you appear to make I disagree with....that it is incorrect to speak of current as having a direction. The are multiple uses / definitions of the work "current" in play and you appear to be basing your argument on limiting this to only one of them.....the mathematical quantification one. Another common one is to generally refer to the movement of electricity in a circuit, and in that case it does have direction, with the convention being to describe that direction in terms of positive flow. Or perhaps I misunderstood your intended points. Sincerely, North8000 (talk) 13:12, 17 December 2018 (UTC)

What does the ampere measure?

The second paragraph in the introduction starts with the sentence:

The SI unit for measuring an electric current is the ampere, which is the flow of electric charge across a surface at the rate of one coulomb per second.

Read literally, the first phrase seems to say that the unit is used to measure current, but a unit does not measure, it is used only to indicate a quantity of a measured physical quality, which can then be used to give a measure. Shouldn't the sentence indicate more clearly what physical quality is being measured? And the second phrase "the unit ... is the flow" seems to put emphasis on flow, but that is the quality, when the quantity of the unit should be in focus. I could not formulate a satisfactory alternative. - Here is a flawed attempt, which I hope will inspire a more precise formulation.

Electric current is measured in terms of amount of charge per second. This rate describes an intensity. The SI unit for this intensity is the ampere, where one ampere means that one coulomb of electric charge flows past a cross-section in one second.

And perhaps the other sentence in the paragraph should indicate more clearly what is being measured, and not only what instrument was used. Again, a flawed attempt:

The amount of amperes in an electric current is measured with a device called an ammeter.

Sdc870 (talk) 04:39, 8 March 2019 (UTC)

clarifying the role of heat in Joule heating

Here is the text, from Serway and Jewett (2004, p. 846) that I was citing.

The process by which power is lost as internal energy in a conductor of resistance R is often called joule heating5; this transformation is also often referred to as an I2R loss.

And footnote 5 in full:

5It is commonly called joule heating even though the process of heat does not occur. This is another example of incorrect usage of the word heat that has become entrenched in our language.

As I wrote in the explanation: thermodynamic work is involved in moving electrons through a conductor, which increases internal energy of the conductor (i.e., gets hotter). The physical concept of heat is not involved in the power dissipation (i.e., Joule heating). If I have misunderstood, then happy to get the matter corrected. Sdc870 (talk) 01:54, 16 April 2019 (UTC)

Thanks for starting the discussion here. I'm not quite sure what the author is trying to say in their footnote, but the "physical concept of heat" (whatever that means) is quite obviously involved in the Joule heating exhibited by a resistance heater. This is clearly sourced at our main article for Joule heating, for example [1]. Put another way, Joule heating is an example of an irreversible process that necessarily does involve heat. You seem to be stating that the heating of a conductor is proportional to the amount of power (work) flowing through it, but we know that isn't the case: a high-voltage DC transmission line is substantially cooler than the heating element of a space heater, despite carrying many orders of magnitude more power. VQuakr (talk) 02:07, 16 April 2019 (UTC)

I agree with VQuakr regarding the article content. But, as a sidebar, I didn't see anything that implied that "the heating of a conductor is proportional to the amount of power (work) flowing through it". Sincerely, North8000 (talk) 02:43, 16 April 2019 (UTC)

Fair enough, I must have misunderstood about the sidebar part. VQuakr (talk) 03:52, 16 April 2019 (UTC)

Reference direction subsection

Of course the convention is to specify current as that of positive flow. Other than attempting to say that, IMO this whole subsection is a confusing mess that does not cover any common practice. What do others think about this? Sincerely, North8000 (talk) 14:02, 5 May 2020 (UTC)

I'm sure that the section could be improved, but it describes the usual process when solving a circuit. You assign a reference direction and then determine whether the current is positive or negative with respect to that direction. Constant314 (talk) 14:12, 5 May 2020 (UTC)

?? Well, the implicit standard of defining current as positive flow is always there, and that definition is presumed/utilized in circuit analysis. Beyond that, IMO circuit analysis determines everything about current, you don't "assign" anything. But let's get feedback from others.North8000 (talk) 14:25, 5 May 2020 (UTC)

Here is a quote from the Hayt, "The arrow is a fundamental part of the definition of a current." Constant314 (talk) 14:29, 5 May 2020 (UTC)

Cool if you'd like to discuss what the source says, but could you give us more than that? Sincerely, North8000 (talk) 15:19, 5 May 2020 (UTC).

Not sure what you are looking for. The article makes perfect sense to me, but I've been solving circuits for years. Is there something in the article that is unclear or is there something missing? Constant314 (talk) 15:41, 5 May 2020 (UTC)

In 51 years and counting in electronic design, including 45 as an EE, I have heard of "assigning" a direction of current as a precursor to or as a part of circuit analysis. And so I think that any inference that such is the norm is incorrect and probably not in the source. Also it isn't clear and I don't know what purpose it would serve. Sincerely, North8000 (talk) 19:01, 5 May 2020 (UTC)

When you set up to run a problem in, for example, SPICE, you assign nodes to possibly unknown (to be solved for) voltages, with possibly unknown currents between them. Since you don't know the voltage on all the nodes (which is why you are running the simulation), you often don't know the sign of the currents between them. I suspect many people, if they do know the sign, will assign the current direction such that it is positive, but when you don't know it, you choose one direction. Gah4 (talk) 19:21, 5 May 2020 (UTC)

In the olden days with analog voltmeters, one had to choose the probe positions for a positive reading. Digital voltmeters will nicely place a minus sign on the display if we guess wrong. Most of the time, I don't even try to guess, just connect the probes and see what happens. Gah4 (talk) 19:21, 5 May 2020 (UTC)

Here is what Hayt says on page 29: On page 29: “Our first step in the analysis is the assumption of reference directions for the unknown currents.”Constant314 (talk) 22:07, 5 May 2020 (UTC)

bound to the individual atom

The article says: In a metal, some of the outer electrons in each atom are not bound to the individual atom as they are in insulating materials. Note, though, in semiconductors and insulators the valence electrons are normally not bound to individual atoms, either. They are delocalized in a full valence band, which conducts no current. There are electrons moving all directions up to the Fermi velocity. Gah4 (talk) 05:25, 11 November 2020 (UTC)

That's true. Mind correcting? WP:BEBOLD Ponor (talk) 09:34, 11 November 2020 (UTC)

Needs a history section

eg.

• First recognised by Stephen Grey, 1729.
• First crudely measured by maybe Martinus van Marum's electrolysis experiments ~1785, as masses of particular metals deposited per hour.
• First steady/chemical generation Volta, 1800.
• First electromagnetic current measurements maybe about 1820 by Ørsted. - Rod57 (talk) 15:50, 1 February 2021 (UTC)

@Rod57: from my (limited) experience on Wikipedia: if you don't add this - citing reliable sources - no one else will add it. So please, WP:BEBOLD. Ponor (talk) 16:40, 1 February 2021 (UTC)

The references from Oersted's article are:

References

Article needs a link out to the article on Solenoid

Because of the article Semi-protection, I'm unable to edit. However, there are at least two mentions of the physical structure of a Solenoid being important in many types of electromagnetic circuits; and no links out to the wonderful article on Solenoid. Someone with the power and authority may wish to at least link the current mentions, and perhaps furthermore to describe the important correlation between electric current and solenoid circuits. — Preceding unsigned comment added by Zx3junglist (talk • contribs) 20:34, 25 February 2021 (UTC)

Done. @Zx3junglist: BTW, for the kind of protection that this article has, once you make 7 more edits on Wikipedia (= become an autoconfirmed user) you'll have the "power and authority" to edit it.  :-) North8000 (talk) 21:57, 25 February 2021 (UTC)

Electrocution

Why isn't electrocution mentioned on this page? The effects/interaction of electric current on humans/tissue should be mentioned. — Preceding unsigned comment added by 184.2.141.98 (talk) 17:00, 5 March 2021 (UTC)

Of course, it's related, but so are 1,000 other topics which involve electric current that are equally related so IMHO we should stick to things more closely relevant. North8000 (talk) 21:13, 5 March 2021 (UTC)

We do mention electrocution at Electricity briefly, with a link to the main article, electric shock. Physiological effects are not relevant enough to mention at this more detailed article. VQuakr (talk) 02:13, 6 March 2021 (UTC)

What are the types of current

Basically , according to my knowledge there are two types of current. 1. AC(Alternate current) and 2. DC(Direct current) — Preceding unsigned comment added by My264 (talk • contribs)

We touch on this at Electric current#Alternating and direct current. But it is the same current; AC and DC just refer to different waveforms. DC is a constant, a straight line; AC is a repeating pattern (typically a sine wave). With a signal generator you could create other waveforms: sawtooth, square wave, etc. But it still would be the same current just modulated differently. FYI, the best place to ask general questions about a science topic is WP:RD/S. VQuakr (talk) 16:22, 17 June 2021 (UTC)

There are the common meanings / situations for those terms (mostly for supply of power) and then there are those which they hypothetically cover but where they are really not used. Examples of the latter are that signals and RF are technically AC. North8000 (talk) 17:09, 17 June 2021 (UTC)

these electrons move about randomly due to thermal energy

The article says" these electrons move about randomly due to thermal energy but that isn't quite right. They are moving at up to the Fermi velocity, with most of them close to that. And close to equal in all directions. (Not quite equal, as the Fermi surface is only approximately a sphere.) In a not-full band, a few more electrons can move one way, and a few less the other way, resulting in a net current. But yes, if you just include the states near the Fermi surface, the result is a good approximation to random thermal motion. Do note, though, that increased temperature increases the scattering and decreases the conductivity. Gah4 (talk) 23:32, 26 January 2022 (UTC)

Science

What constitutes an electric current? 2409:4066:E87:A274:4D70:A2AC:A716:9FA (talk) 12:19, 12 February 2022 (UTC)

The answer is close by at Electric current :-) North8000 (talk) 18:31, 12 February 2022 (UTC)