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In most text books and other electronics material it's said current is flowing through the circuit. Isn't this wrong? As current is flow of charge. Is there anything such as flow of flow of charge?

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  • \$\begingroup\$ It's a common, harmless redundancy. \$\endgroup\$ – Alfred Centauri Mar 21 '13 at 19:07
  • \$\begingroup\$ "Current is flowing" does not equal "flow of flow of charge" it equals "flow of charge is flowing" \$\endgroup\$ – DrFriedParts Mar 21 '13 at 19:39
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    \$\begingroup\$ It's like saying a river is flowing. Actually the river stays in the same place and only the water in the river flows. However, it is common to talk about "current flow", and everyone that isn't trying to be anal will know what you mean. \$\endgroup\$ – Olin Lathrop Mar 21 '13 at 20:03
  • \$\begingroup\$ Not exactly harmless. In my experience, the main source of public confusion over the nature of electricity is the wrong idea that "current" is like a substance, and that "current" can move around inside the wires. At the same time, most people aren't aware that metals are already full of mobile charges. Where did they get these misconceptions? Probably from explanations about "flow of current," where flows of charge are never mentioned. Me, I find that muddled concepts become very clear if the phrase "flow of current" is carefully avoided, and instead we teach about "flow of charges." \$\endgroup\$ – wbeaty Apr 1 '13 at 4:37
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"Flowing" qualifies state of flow

"Current is flowing" implies current not equal to 0.

It's semantically correct. Same as, "The river is flowing."

Websters, #2: River: A large quantity of a flowing substance

It describes the degree to which the flow is occurring (e.g. not zero).

The presumption of the question is wrong

"Current is flowing" does not equal "flow of flow of charge"...

...it equals "flow of charge is flowing."

At worse, it's redundant (not wrong). Typically it's just used as I described above (to indicate a non-zero quantity).

For non-English majors (like me!), here is more detail on this specific use case from english.SE.

Essential vs. temporary attribution

Here's a highlight from the English community (user Choster, a professional writer in Washington, DC):

We would identify something as a river because we ordinarily expect it to have the characteristics of a river, even if some of those characteristics are temporarily suspended. That is, a permanent or semi-permanent stream would be a river even if it has temporarily stopped streaming, as noted in the comments, by drying up, being dammed up, or being frozen solid.

On the other hand, something which only temporarily takes on the characteristics of a river could be called so, metaphorically, but only while it possesses those characteristics. If they cease, the metaphor is no longer applicable. If I spill a jar of molasses, I may report a river of molasses running down the table leg, but once the flow stops, we would lose the river (having gained a pool).

Current is a flow and flows may be interrupted, suspended, and resumed. A charge does not lose its ordinary expectation to flow just because it is momentarily not moving.

Flow is a rate

Electric current is the rate of movement, not strictly "electric charge in motion". Because this difference is subtle and has little impact on day-to-day design and analysis work, it's largely ignored (as it should be).

A quantity "charge in motion" would have units of yes/no -- is it "charge in motion" or not? To be more useful we need quantities that describe the motion.

That is why current is defined as the rate at which charge transits a normal surface. That is, current is the flow of charges, described by how much charge moves in unit time.

Perhaps it is more illustrative to see that "velocity" is not "meters in motion," even though velocity is describing the motion in units of meters (per unit time).

Another way to intuitively grasp this idea is to work backwards. In ordinary practice we readily except the idea of "zero as a number" and in engineering (especially appertaining current) doubly so -- "The current into the lightbulb is 0-Amps."

The reason current can be 0, as a quantity, is because it is describing a rate.

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  • \$\begingroup\$ The river is flowing with water; the current is flowing with electrons (but the other way). Sorry!! \$\endgroup\$ – Andy aka Mar 21 '13 at 18:41
  • \$\begingroup\$ @Andyaka but he never said in the river reference that the current was flowing, he said the river was, and in electronics we dont have different names. \$\endgroup\$ – Kortuk Mar 21 '13 at 19:15
  • \$\begingroup\$ "Current is a flow and flows may be interrupted, suspended, and resumed." Electric current is, physically, electric charge in motion. You're using the word "flow" in two different senses - that's equivocation - a logical fallacy. \$\endgroup\$ – Alfred Centauri Mar 22 '13 at 20:34
  • \$\begingroup\$ @AlfredCentauri back to my text books I go. I will be doing maths. \$\endgroup\$ – Kortuk Mar 22 '13 at 21:12
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    \$\begingroup\$ @kortuk: "I will be doing maths". May the gods help us! \$\endgroup\$ – Alfred Centauri Mar 22 '13 at 22:36
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See this website about common electricity misconceptions. The author, William Beaty, addresses your question exactly:

THE STUFF THAT FLOWS THROUGH WIRES IS CALLED 'ELECTRIC CURRENT'? Horribly misleading!

Most K-12 textbooks discuss a substance or energy called "current". They constantly talk about "flows of current." However, here's a pointed question: what flows in rivers? Is it water, or is it "current?" If I fill a bucket from the faucet, is my bucket full of "current?" No! Water moves, water flows in pipes, not "current." A flow of water is a correct phrase, while "a flow of current" is not. The same idea applies to electricity: electric current is a flow of a substance, but the name of the substance is not "current."

Since a current is a flow of charge, the common expression "flow of current" should be avoided, since literally it means "flow of flow of charge." --Modern College Physics: Sears, Wehr, & Zemanski

. . .

Go check out his website -- he talks about several similar misconceptions.

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  • \$\begingroup\$ Beat me to it by just a few seconds! \$\endgroup\$ – Alfred Centauri Mar 21 '13 at 19:04
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    \$\begingroup\$ "Flows of Current" is clearly wrong. But that isn't the question the OP asks. It's "Current is flowing" <-- which is actually quite correct in the English language. \$\endgroup\$ – DrFriedParts Mar 21 '13 at 19:38
  • \$\begingroup\$ Here's a pointed question: if you are running a waterwheel, do you care about water, or current? Please show me an electrical component that operates like a bucket. \$\endgroup\$ – Phil Frost Mar 22 '13 at 21:03
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This is a subject matter for http://english.stackexchange.com. and perhaps http://ell.stackexchange.com

Natural language cannot be read by macro-expansion of words with their definitions. You have to process language semantically, and not in a machine-like manner.

Flowing is what a flow does. A flow of charge flows through a circuit, hence a current flows. The charge flows also.

But if we ask what is the flow of, it is a flow of charge, not a flow of the flow of charge (even though the flow of charge flows). A flow does have a flow rate, however. What is the flow rate of that flow? is a grammatical question. We can elide the first flow in that sentence, but we can also elide rate: What is the flow of that flow? The first flow refers to the quantity, and second to the phenomenon.

Do you also suspect that it's wrong to say that a river flows, because it is actually water that flows whereas the river stays where it is? The idea of such a semantic restriction runs contrary to numerous human languages from all over the globe.

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  • \$\begingroup\$ Good point. "Wind blows" and "current flows" are fine for everyday conversation. Physics explanations are different, and there we'd use strict and narrow meanings. There we'd typically require machine-like replacement of terms with their definitions. "Current flows" is unscientific, redundant, and perhaps even misleading to students, since current = charge flow. Charges flow, while currents arise and vanish, and while their charges are flowing, the currents may sit unmoving within circuitry. (So, when a pattern of current shifts position, only that would be a "flow of current?") \$\endgroup\$ – wbeaty Apr 1 '13 at 5:12
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You're right - it's redundant but it is commonly used.

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I don't see anything wrong with it. Can we talk about wind blowing or a gust of wind? Wind is, by definition, a flow of air. Wind is the word we use for air when what we care about is the air's movement, and not really the air. Yet, we wouldn't complain about gusts of wind, would we? If gusts of wind are valid, what's wrong with flows of current?

Even when there is no electromotive force, the current flow is still defined. It is zero, which is different than saying it doesn't exist, or is otherwise invalid. On a stagnant day, wind doesn't become air. The wind is still there. It is zero. Nor on a windy day does the air does become wind.

It would make sense that electrical engineers would favor current over charge, because charge that isn't moving generally doesn't do anything useful to the electrical engineer, as air that isn't moving can't do anything useful to the windmill operator.

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    \$\begingroup\$ I don't think "runners running" is a good example. A runner, in this context, is, e.g., a person who runs competitively as a sport or hobby. To say that a person is a "runner" is not to say that the person is running. However, a current is not a charge that sometimes moves, a current is charge in motion. If the runner stops running, she is still a runner. If the charge stops moving, the charge is not a current. \$\endgroup\$ – Alfred Centauri Mar 22 '13 at 19:22
  • \$\begingroup\$ @DrFriedParts I'd like to see you do anything useful with a capacitor without ever moving any charge. "Electrostatic" is just another way of saying not moving much charge. It still moves, or did at one point, or will eventually. \$\endgroup\$ – Phil Frost Mar 22 '13 at 20:45
  • \$\begingroup\$ @AlfredCentauri No, in this context, a runner is someone who is running in a race. As in, "seven runners will be participating in today's event," not, "I met this very interesting runner at the bar last night." The runner has no purpose but to run, as in electrical engineering the charge has no purpose but to be pushed around by electromotive force. \$\endgroup\$ – Phil Frost Mar 22 '13 at 20:57
  • \$\begingroup\$ @PhilFrost, your further clarification doesn't remove the essential problem with your example. This is yet another example of equivocation. If your runners are those "running in a race", they are runners before the race starts ("runners will be participating...") and after the race ends ("runners participated...") even though, before and after, they aren't necessarily physically running, i.e., they may be walking. Electric current is electric charge in motion and not electric charge that will be in motion or that has been in motion, but is in motion. \$\endgroup\$ – Alfred Centauri Mar 22 '13 at 22:32
  • \$\begingroup\$ @Alfred -- A current is not a "charge in motion". A charge in motion creates a current, but they are not identical. I don't think you correctly understand the concept of a "flow". You are welcome to your own interpretation, but you should understand that it is inconsistent with the English language and professional practice. \$\endgroup\$ – DrFriedParts Mar 23 '13 at 2:33
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Strictly speaking, yes, current is a flow of charge. When it comes to a flow of anything, be it charge, water, or hydraulic fluid, a rate needs units attached to it. For convenience, we use the relationship \$1A=\dfrac{1C}{s}\$.

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  • \$\begingroup\$ 1A = 1C/s is not merely a convenience, it is a definition. \$\endgroup\$ – Olin Lathrop Mar 21 '13 at 20:05
  • \$\begingroup\$ True, my point was it's a lot easier to carry through calculations and to talk about, vs. what makes physicists happy. \$\endgroup\$ – Matt Young Mar 21 '13 at 20:09
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According to dictionary.com, "flowing" is an adjective and, in this context, is defined thus:

moving in or as in a stream: flowing water.

Thus, "flowing charge" or "charge is flowing" means charge (is) moving in or as in a stream.

Now, charge moving in or as in a stream is precisely what we think of as "electric current" in a circuit context.

Then, "flowing current" or "current is flowing" is, literally, charge moving in or as in a stream is moving in or as in a stream.

Thus, if "current is flowing" means something else, then either "current" or "flowing" is being used in a different sense.

DrFriedParts proposes in his answer that "current is flowing" equals "flow of charge is flowing" and that this describes the degree to which the flow is occurring (e.g. not zero).

There is, in fact, a sense in which "flowing" describes degree:

abounding; having in excess: a land flowing with milk and honey.

So, it seems, "current is flowing" isn't redundant if "flowing" is used in this or a similar sense. Although flow of charge is abounding isn't precisely the same as flow of charge is non-zero, it's certainly in the ballpark.

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