Talk:Electric current

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amperage?[edit]

"amperage" redirects to this article, but amperage is never mentioned in the article.

The dictionary says that amperage is the strength of an electric current, but that's hardly a complete explanation. 69.150.11.22 (talk) 21:47, 7 March 2014 (UTC)

It's simply a rather informal expression for an amount of electric current measured in amperes. Similarly, wattage redirects to electric power. There is really not any more to say about it than the dictionary definition and Wikipedia is not a dictionary, we have Wiktionary for that. SpinningSpark 23:59, 7 March 2014 (UTC)

but direction when the opposite some time they are i mean charge is equal run i saw this — Preceding unsigned comment added by 182.188.193.87 (talk) 17:36, 15 March 2014 (UTC)

Suggestions, since article is semi-protected[edit]

  • "In metallic solids, electric charge flows by means of electrons, from lower to higher electrical potential."
In a simple battery-resistor circuit, electrons flow from negatively charged battery terminal to positively charged battery terminal. This is the (spontaneous) direction of flow, in which battery discharges. Positively charged terminal is the high potential terminal for conventional flow and low potential terminal for electron flow. Whatever you assume to be flowing (positive or negative charge carriers), the flowing thing is moving from a point of high electric potential, towards a point of low electric potential. This is the natural direction of flow; from high potential to low potential: For a falling rock, gravitational potential energy decreases; for (spontaneous) thermodynamical processes, thermodynamic potential of the system decreases; for orbiting bodies (macro or micro), force field moves the body in the direction of decreasing potential energy associated with the field (gravitational or electrostatic). Potential energy (of any kind) is the energy stored in the force field; when the state of the object is allowed to be altered only by the field, the potential energy decreases. This is the meaning of "potential energy"; it decreases in spontaneous processes/flows, among which is the discharging of a battery.
If you are an electrical engineer and (probably because of that) considering conventional flow, charge carriers have positive charge, and they flow from high potential terminal (positively charged terminal) to low potential terminal (negatively charged terminal).
If you are solid state physicist and (because of that) considering electron flow, charge carriers have negative charges, and they flow from high potential terminal (negatively charged terminal) to low potential terminal (positively charged terminal).
By convention high electric potential always means more positive and low potential means more negative, so positive charge carriers tend to flow from high potential to low potential and negative charge carriers tend to flow the other way. That is the convention whether you are an engineer or a physicist.Constant314 (talk) 23:03, 20 March 2014 (UTC)
Finally, "electric charge flows by means of electrons": How about, "flowing electric charge is carried by electrons", or "electrons are the flowing charge carriers", or "electric charge is carried by electrons".
I don't see a great difference in all these possibilities so I'm inclined to leave it the way it is.Constant314 (talk) 23:03, 20 March 2014 (UTC)
  • "In electronics, other forms of electric current include the flow of electrons through resistors or through the vacuum in a vacuum tube"
Is there something that separates electric current through a 1.5mm copper wire and electric current through a 10 megohm ceramic resistor. The resistance mechanism is lattice scattering in DC, whereas skin and proximity effects (self&externally induced eddies) join the club in AC, and club changes the name to impedance. This is the way a conducting medium resists to flowing charge carriers: Lattice atoms in thermal motion scatters flowing charge carriers, and an alternating magnetic field (if-exists) induces eddy currents. So, how about we stop considering "flow of electrons through resistors" as 'another form of electric current'. Or, while we are at it, we could also list a few other circuit elements to enrich the content, e.g., electric current through inductors, electric current through diodes, electric current through human body, etc.
Off hand, I would not expect the conduction mechanism of resisters to be a lot different from metals, but the rest of the sentence does not seem too redundant. And there is the "excess noise" effect in some resisters so there may be indeed some other type of conduction, but there does not seem to be any point of mentioning without explaining it. It probably could use some wordsmithing, but its not egregiously incorrect.Constant314 (talk) 23:03, 20 March 2014 (UTC)
  • "The theory of Special Relativity allows one to transform the magnetic field into a static electric field for an observer moving at the same speed as the charge in the diagram. The amount of current is particular to a reference frame."
How about, "the same speed as a flowing charge" instead of "the same speed as the charge in the diagram".
That whole sentence needs work. It looks like it was tacked on after the figure was added. I'm inclined to delete it.Constant314 (talk) 23:03, 20 March 2014 (UTC)
  • "A solid conductive metal contains mobile, or free electrons, originating in the conduction electrons."
If you call it metal, you implicitly call it conductive (or conductor), and vice versa depending on the context.
Acceptable redundancy. Not obviously implicit to everyone.Constant314 (talk) 23:03, 20 March 2014 (UTC)
'free electrons originating in conduction electrons': Both the introductory text of Callister, and Kasap's graduate text avoids using "conduction band", in text and in diagrams, for metals; metals do not have an energy gap between occupied energy states and free energy states, semi-conductors and insulators have the gap. Valence electron is not a free electron, a free electron is an electron excited to one of the emtpy energy states by an applied electric field. When a valence electron is freed, it becomes a free-electron.
At least, how can it "originate in conduction electron", i do not know. ('originate in' or 'originate from'?) — Preceding unsigned comment added by 85.110.37.26 (talk) 12:28, 20 March 2014 (UTC)
Yes, it does not make sense as written.Constant314 (talk) 23:03, 20 March 2014 (UTC)
In the section about reference direction, what exactly is meant by the term "positive current"? I guess it means the direction of the flow of positive charges but it could mean the direction of the flow of charged particles - it wouldn't go amiss to be clear about this.Quill14 (talk) 23:06, 12 November 2014 (UTC)
It is the direction positive charges are going or opposite the direction that negative charges are going. If a wire has 1 amp of electrons moving from right to left, I can draw the current vector right to left or left to right. If I draw it in the same direction that the electrons are moving, then the numerical value of the current vector is -1 Amp. It is negative because the charge carriers are negative. If I draw the vector the the other way, I have to also reverse the sign of the numerical value to +1 amp. Which is a long way of saying that the direction of positive current is the direction in which the numerical value for the current vector is positive.Constant314 (talk) 00:05, 13 November 2014 (UTC)

Metals: free electrons, conduction electrons[edit]

The sentence "A solid conductive metal contains mobile, or free electrons, originating in the conduction electrons" is a bit awkward. Assuming the Wikipedia articles about free electrons and conduction electrons is correct it would seem that any material can have conduction electrons given enough energy but free electrons are only found in metal where they also function as conduction electrons. Or maybe they are conduction electrons. I'll change it to function as. Someone who knows better is welcome to fix it better.Constant314 (talk) 23:16, 20 March 2014 (UTC)

Electromagnet: special relativity.[edit]

The sentence "The theory of Special Relativity allows one to transform the magnetic field into a static electric field for an observer moving at the same speed as the charge in the diagram." is incorrect or ambiguous for the diagram. Probably one would need a speed where the current of electrons going one way was equal to the current of atomic nuclei going the other way. Anyway, SR transformation of the magnetic field is probably out of scope for an article on current.Constant314 (talk) 23:32, 20 March 2014 (UTC)

I think it is reasonable to have a mention of SR here, or at least a link to an explanatory article for readers who wish to know more. It is no more out of scope than the following section on radio waves. The magnetic field is intrinsically linked to current flow, it is inseparable from it, and SR is required to fully understand this. By the way, you are mistaken in thinking that a frame where the positive and negative charges have equal and opposite velocities would result in the magnetic field transforming to zero. The currents of the two lines of charges have equal and opposite velocities, but because the charges are of opposite sign both currents are equal (ignoring relativistic foreshortening which will be negligible at the velocites involved in regular conductors) and in the same direction. Thus their magnetic fields will add. I do not believe that the magnetic field of an overall neutral current carrying conductor can be transformed to zero in any frame. Nor can the current be transformed to zero if it was not zero in the rest frame. SpinningSpark 16:06, 26 March 2014 (UTC)
Yes, the currents would add and the field would not cancel. I'll stick with the sentence being "incorrect or ambiguous". As for scope, I think SR is two steps away. An article on current could reasonably discuss magnetic fields and an article on magnetic fields could reasonably talk about SR. But I would not object to a statement or section that was factually correct and not misleading on the grounds of scope.Constant314 (talk) 22:29, 26 March 2014 (UTC)

International System of Quantities[edit]

The International System of Quantities (ISQ) is not the same as the International System of Units (SI). Furthermore, the ISQ is defined by the BIPM as "system of quantities having the base quantities: length, mass, time, electric current, thermodynamic temperature, amount of substance, and luminous intensity", making it directly relevant to this article. Dondervogel 2 (talk) 16:53, 7 April 2014 (UTC)

I've reverted, I guess you're right. SpinningSpark 22:26, 7 April 2014 (UTC)

Light radiation[edit]

"Electric currents can result in the radiation of heat and light." - [1].

While it is technically true, this is misleading. Current can cause light by two effects :

  • light emitted by incandescence is due to heat, which is itself due to the current by Joule heating ; contracting the causality link is disputable, even for a lead section.
  • alternating current emits radio waves (ie electromagnetic radiation), and "light" is a particular kind of those waves : the ones with wavelength in the 400-700 nm range (roughly). A back-of-the-enveloppe calculation shows that those wavelengths correspond to frequencies of the order of 10^15 Hz, way out of the usual range for electric currents (home electricity is ~50Hz, basic oscilloscopes go up to the GHz range (10^9 Hz)). I doubt anyone except maybe optics experimentalists have ever seen light from alternating current...

I changed the lead to something less, hmm, misleading.Tigraan (talk) 12:31, 9 February 2015 (UTC)