Electric current comes in many forms: current in a wire, flow of ions between the plates of a battery and between plates during electrolysis, as arcs, sparks, and so on. However, here on Hackaday we mostly deal with the current in a wire. But which way does that current flow in that wire? There are two possibilities depending on whether you’re thinking in terms of electron current or conventional current.
In a circuit connected to a battery, the electrons are the charge carrier and flow from the battery’s negative terminal, around the circuit and back to the positive terminal.
Conventional current takes just the opposite direction, from the positive terminal, around the circuit and back to the negative terminal. In that case there’s no charge carrier moving in that direction. Conventional current is a story we tell ourselves.
But since there is such a variety of forms that current comes in, the charge carrier sometimes does move from the positive to the negative, and sometimes movement is in both directions. When a lead acid battery is in use, positive hydrogen ions move in one direction while negative sulfate ions move in the other. So if the direction doesn’t matter then having a convention that ignores the charge carrier makes life easier.
Saying that we need a convention that’s independent of the charge carrier is all very nice, but that seems to be a side effect rather than the reason we have the convention. The convention was established long before there was a known variety of forms that current comes in — back even before the electron, or even the atom, was discovered. Why do we have the convention? As you’ll read below, it started with Benjamin Franklin.
Franklin’s Experiment
To give you some idea of just how early we’re talking about in the field of electricity’s development, the Leyden jar, the first capacitor, had just been invented in 1745. Word of it, and other discoveries were spreading rapidly through letters and lectures. One such lecturer was Dr. Archibald Spencer. Franklin attended his lectures and even bought Dr. Spencer’s equipment in 1746.
Franklin was a prolific and rigorous experimenter and began writing his own letters about his work and his theories. It’s through those letters that we have the details of the experiment from which we get our direction for conventional current.
In a few letters he described an experiment with persons A, B anc C. Persons A and B stand on wax to insulate them from the ground, whereas C stands directly on the ground. Person A rubs a glass tube against his hand and, as Franklin describes it, “collects the electrical fire from himself into the glass”. B then passes his knuckle near the glass tube and “receives the fire which was collected by the glass from A”. But to C, both A and B appear electrified “for having only the middle quantity of electrical fire, receives a spark upon approaching B,” or “gives one to A, who has an under quantity”. If instead, A touches B then the spark is stronger because the difference between them is greater. If after A and B touch, C touches either of them there is no spark because “the electrical fire in all is reduced to the original equality”.
Franklin’s Explanation
Franklin’s letter then continues by defining some new terminology and establishing the convention that we use today.
“Hence have arisen some new terms among us: we say, B, (and bodies like circumstanced) is electrified positively; A, negatively. Or rather, B is electrified plus; A, minus. … To electrify plus or minus, no more needs to be known than this, that the parts of the tube or sphere that are rubbed, do, in the instant of the friction, attract the electrical fire, and therefore take it from the thing rubbing: the same parts immediately, as the friction upon them ceases, are disposed to give the fire they have received, to any body that has less.”
Thus, Franklin came up with the idea that charge is something that moves from the positive to the negative, or from that which has more to that which has less. That’s the conventional current that was adopted and that we use today.
Note that by rubbing objects together as described in the letters, they’re making use of the triboelectric effect to charge the objects. Just which objects get charged positively, giving up electrons, and which get charged negatively, taking the electrons, is listed in a table called the triboelectric series. From the letters, Franklin correctly deduced which charge different objects will get, glass being charged positively and sulfur negatively, for example.
The problem is that when you get a spark from going near the positively charged glass, Franklin guessed that the electric fluid moved from the positive glass to you, whereas we now know it’s you that give electrons to the glass.
Ebenezer Kinnersley, who was a part of Franklin’s close circle of electrical experimenters is also often credited with this idea so it’s hard to know if only one person came up with it or if it was a result of a collaboration. Franklin seems to hint at the latter when in the letters he writes “And we daily in our experiments electrify bodies plus or minus, as we think proper.”
Faraday’s Current-Direction Dilemma
In the 1800s, Michael Faraday ran into similar problems of having to name charge carriers without having a full understanding. He’d done some experiments with electrolysis and, while working on a paper about them, needed names for what we now call the cathode and the anode.
The two plates of his electro-chemical cell were connected to an electrical circuit and so there was a positive plate and a negative plate. As we saw above, the convention was that in the circuit around the cell, the current left the positive plate and entered the negative plate. After deciding what to call the plates, electrodes, he then needed to distinguish between the two from the point of view of how the ions inside were interacting with them. He also wanted names that were fairly independent of theory.
He looked to an analogy with the Earth’s magnetic field and the direction the current would have to run around the Earth in order to create the fields — that would be the same direction as the sun, east to west, or going up in the east and going down in the west. His friend, William Whewell, suggested kata, Greek for downwards, and odos, Greek for a way, i.e. the way which the sun sets. The result is “cathode”. Similarly using ano, Greek for upwards, resulted in “anode”.
Interestingly, in the same paper, after offering these names, he shows his concern in naming things while it was still early days in their understanding. He writes “and whatever changes may take place in our views of the nature of electricity and electrical action … there seems no reason to expect that they will lead to confusion, or tend in any way to support false views.” Sure enough, due to the discovery of the electron and the fact that the moving charge carrier’s direction is actually the opposite, it’s been suggested that kata odos, the way down, can now be interpreted as the way down into the cell, i.e. where the electrons enter the cell.
Thomson’s Discovery Of The Electron
The discovery of the real charge carrier in a wire, the electron, started out with research into cathode rays. Cathode rays were first observed as a glow emitted from the cathode in a rarefied gas. In the 1870s, Sir William Crookes produced the first cathode rays in a high vacuum and showed that they moved from cathode to anode. He also used a magnetic field to deflect them and realized that they were negatively charged.
But it was J.J.Thomson in 1897 who realized that the rays were actually unique particles and made good estimates for the particle’s charge and mass. He called them ‘corpuscles’ but their name was later changed to ‘electron’. Thomson also found that they are what are being given off by incandescent light and by the photoelectric effect and it wasn’t long after that they were found be the charge carrier for electricity in wires.
Does It Matter?
It turns out that whether you use conventional current or electron current doesn’t matter, as long as you’re consistent in your use. Kirchhoff current law, for example, says that the sum of the current going into a junction (node) in a circuit is the same as the sum of the current going out of the junction. It doesn’t care which directions are in and out, as long as you keep track of the signs.
However, conventional current is represented in the shapes of various components in schematics. The ‘arrowhead’ shape of a diode points in the direction of conventional current, as do the ‘arrowhead’s in transistors. But it’s easy to remember that electrons flow against the arrows. The right-hand rule also uses conventional current when figuring out the direction of the Lorentz force or the direction of the magnetic field around a current carrying wire. So it seems you do at least have to be familiar with conventional current.
The Winner’s Circle
Which did you first learn? Which do you prefer? Do you use conventional current for some things and electron current for others? In my experience producing corona discharges across air gaps, it matters whether or not the sharp electrode is providing the electrons since the resulting coronas are produced differently. Share your experience and opinions in the comments below.
As always, there is an XKCD comics covering this topic: https://xkcd.com/567/ .
That was an interesting 30 minutes….
I usually go with conventional current when I am trying to design something, it seems easier for me. It wasn’t until about when I was 25 years old that I learned electron flows from negative to positive, opposite of conventional current. A lot of schematic symbols were designed with conventional current in mind.
I am in the same theoretical boat here.
I learned electronics from kits and the books and schematics all highlighted conventional current. With a nice liner note at the end pointing out “hey, remember everything is backwards now…”
Only thing to watch out for is which one one’s textbook is using.
And in that vein something free.
https://www.circuitlab.com/textbook/
I have yet to look through the circuit lab book. When some ask about free print instructional material, pot the them to archive.org to search for NEETS. Navy Electricity Electronics Training Naval Series/Navel Electrical Engineering Training Series. I generally don’t point people to the ARRL basic electronics publication, because of the silly pig cartoon illustrations, then again Adafruit’s instructional videos contain a cartoon character.
I was going to post essentially the exact same thing Eric. Even my age was about the same. At first I struggled with it, then realized that I was overthinking it.
I remember in my college entry level electronics course the professor brought this up, although he referred to it as Electron Flow theory and Hole Flow theory. Brings back memories of that course… (most of which was fairly easy, this was one of the interesting things I actually learned about)
conventional, electron, conventional
electron
yes
Current is a definition. For the most part, what is carrying the charge is not relevant, and the statement “So it seems you do at least have to be familiar with conventional current” misses the point. I would state it “There are cases where you actually are concerned with what the charge carrier is, but they are rare”
I have worked with a number of people that get very, very wound up about this, in the same way as the “tau should replace pi” set. People that will curse Franklin, argue that everything should be renamed because it will be so much easier, and so on. (One did his graduate research in device failures due to whisker formation and electromigration in semicindutor leads. Cognitive dissonance, anyone?)
No one seems to like my arguments that for most things it doesn’t matter, making an issue just confuses students, and there are some new things just hitting the world where the charge carriers are positive (I think they are called solid state semiconductors, or something like that :) ) that can not be analyzed properly without recognizing the positive carriers (no, a positive carrier in a P-type semiconductor is not just an electron moving the other way. Because modern physics)
I would guess that the vast majority of people here have never had a situation where it mattered one whit what the charge carrier was (semicondutor device designers, electron microscopists, electro-chemists, those designing triboelectric and electrostatic induction HV generators– primarily Van de Graff–, and old farts like me that have designed with vacuum tubes likely making the majority).
Now get off my lawn…
I’m with you.
So if unconventional current is electron current then conventional current must be positron current, right?
These days, hole current. Used in p-channel FETs, junction diodes, and BJTs.
I agree with “hole” flow being the best way to describe the ACTUAL way it works. Though some devices clearly want to say ” look… we know how it really works because we are the engineers who finally understood this stuff”… the resulting “why is this backwards” effect when encountering MOSFETS can’t be avoided… The result is the unnecessary divide between pipe smoker engineers and the fingers dirty engineers. In the end… unless you actually design semiconductors… its not as important as just knowing… “it flows when I do this”.
=squints= I can’t tell if you are joking, so I don’t know if I should give a serious answer, or go along with the joke.
There are positive ions that carry charge in some situations.
Off topic slightly but you can tell the direction of current flow with a battery on your tongue. The terminals taste differently. :)
You can teach yourself quite easily to know which is + and – and this can often be helpful. Try it with a AA, don’t be daft and use a car battery.
Do not blow your tongue off. :)
really?! In 40 years of licking batteries, I have never thought to discern this. I usually have both electrodes on my tongue (easy with a 9v, more difficult with an AA – I usually use my cheek for that).
How would you qualify the flavour difference?
I can’t. Just do it with a PP3 and you will notice the difference, Maybe taste is the wrong word, different pain maybe or feeling. That is all taste is anyway so I suppose taste is the right word.
9V makes my tongue twitch. I can sustain a 1.5V. I’m not sure taste is pain (though sometimes pain is tasty? haha).
I would imagine differences in taste might arise from what ions are migrating, and I don’t know what that would be in saliva, and also significantly the metal of the electrode. I’m sure a copper electrode would generate different taste from aluminium or zinc.
I would say: The taste of chili is pain. :-)
Considering a good amount of NaCl in your bodily fluids, you get lye on one pole and chlorine on the other. Which could taste different.
Put it on your tongue then turn it round and put it on your tongue in the same place so that you swap the terminals, you will feel what I mean.
I was taught Conventional Current and it was explained that its the flow of the holes left behind from the electrons flowing the opposite way or hole theory.
I’m surprised you stopped at JJ Thompson as the discovery of electrons leaving a filament was actually discovered by Edison and is recorded in his Patent later known as the Edison Effect. He didn’t understand electron flow but he discovered that he could prevent the black carbon build up on the positive side of the light bulb filament (he used DC not AC) by placing a 3rd positively charged plate inside the bulb to collect the carbon particles. This would lead to the invention of the Vacuum Tube John Fleming and the CRT which JJ Thompson invented.
I thought philo farnsworth invented tge crt
Since conventional current versus charge carrier current was explained to me, I thought these are in fact two different but related phenomenon. The electron flow itself is a slow-moving current from – to +; while the conventional current is the ‘information’ of motion which goes from + to -. This is similar to cars stopped at a traffic light. When it goes green, the first car moves, then the second in the queue and so on. Cars are electron, moving slowly; while the information ‘the preceding car has moved, i should follow’ goes much faster and in the reverse direction.
Probably most readers here have an EE bias, even if they are not actual EEs. I came to circuitry later in life (college), and by that time, I was all scienced up. The profs of both camps resolved the whole thing as “scientists use X, and engineers use the opposite; so deal with it”. (In my optimistic recollection, I don’t recall either insisting that one way was right.) Luckily, I was a math and CS major, so dealing with it was no big deal. Now, when it came to which way the holes were moving, that was a bit mind-altering.
@WJCarpenter, You get it. I’m surprised there are NO comments at my post-time here that understand the difference between “Physics vs. EE” current “direction”. It’s a real thing, and it causes problems, especially when you delve into published papers where the mathematics crosses the boundaries of classical vs. quantum domains. Changing the sign of flow in mathematical proofs and/or simplifications/derivations between the two sign conventions we have today will only propagate throughout the knowledge-base making everything even more difficult to parse. I don’t think we’ll see much (if-any) change when it comes to this problem. All Physicists reading EE papers know about this, and vice-versa! It’s been that way for many-many years To to try and “standardize” at this point would only make things worse. We just have to deal with it.
It’s much simpler to just realize conventional current is the flow of positive charge from the positive to negative terminals. You don’t need to worry about what the real charge carrier is unless you’re working with semiconductor physics, in which case you should be familiar with the concept of holes.
The direction of current is not so confusing. I find cathode/anode much more troublesome. For example battery terminals change their names dependant if it is charged or discharged.
And there is always a guy who shouts “cathode is negative” and refuse to think twise
Yessss! That’s my trouble, too! (and sometimes remembering the direction of the channel arrow in an enhancement mode versus depletion mode MOSFET for the P and N variants).
What’s wrong with “cathode is negative”? Don’t the electrons come out of the cathode?
I am among those who learned science (the physics) before the application of it. I think it is of importance that our language and design represent reality as closely as possible Though some things may not seem like that big of a deal now, problems, workarounds and conditionals have a way of compounding into utter monsters over time.
Defining a fundamental and widely used phenomenon in a way that resembles an elementary school phenomenon known as “Backwards Day” flies in the face of the simplicity and accuracy that science strives for.
It may be true that ‘as long as one remembers’ that “cat” doesn’t necessarily mean positive and “an” doesn’t necessarily mean negative; and that current is the direction of the opposite of any actual particle flow… Then sure, it doesn’t matter! /s
Why don’t we all just speak in double negatives and talk about rivers flowing in the direction that water molecules are departing from?
Because it doesn’t reflect reality in the simplest sense and is therefore a breeding ground for avoidable misunderstanding and eventually, failure.
??? No sarcasm indicated… Perhaps you are confused because you are comparing apples to oranges? The terminals that connected to the anode and cathode components of an active electronic devices aren’t the same as the positive and negative terminals of a battery.
Yeah, my beef is that the cathode is not a positively-charged terminal, but rather where the “holes” migrate to. Which means that the “cat” prefix is not describing the very object that it’s naming, but rather an indirect reference to the positively-charged holes that are attracted to it, and the negatively charged electrons that are migrating away from it. (Anode being the inverse in the same manner.)
To me, it is more intuitive (and consistent) to name something in a directly descriptive manner. Ergo, a cathode should always refer to a positively charged node. This would imply that negatively charged particles are attracted to it, not the vice-versa which is used in conventional circuit descriptions.
Hopefully that’s a better explanation than my originally vague reference. (And hopefully I’m not making a fundamental error in stating it either.)
Can’t stand conventional current. I feel like I’m being dishonest when describing how a circuit works.
You’re only being dishonest if you say conventional current is the flow of electrons. Just don’t say that and you’re fine :)
Prior to the development of vacuum tubes, while polarity was important, the actual direction of current flow in the DC circuits at the time wasn’t a concern. When vacuum tubes, in a practical manner revealed that electrons flowed from negative to positive, minds where blown. The term “conventional current” was invented, so those who work with simple DC circuits could still do so without thinking about electron flow. Science has moved to the point where an electric current needs to be defined as the flow of a an electrical charge. Sure life was easier when the electron was they only charge carrier, however observations have shown there other charge carriers. I’m a grey beard, but I glad I’m able to adapt, because I’d feel dirty if I couldn’t adapt like those grey beards of old couldn’t. A bit disappointment to see that many don’t seem to know when the how the therm conventional current came to be because the modern use is a bit of a misnomer. Not I wouldn’t know what to suggest, because charge flow is a bit awkward.
Several names make no sense when discussion conventional current:
I guess I just trusted that Vss is the SOURCE of the current and Vdd is the DRAIN of the current and everything worked out fine for me. :-)
Also, Open Drain configuration of a transistor only makes sense if the Drain is the open connection, thus the one connected ( to the lower voltage potential) is the source.
So, Electron current FTW.
The source is a source of electrons and the drain is where the epectrons drain into. Conventional current measures the movement of positive charge, which is opposite the flow of electrons.
What about ‘earth’ though?
Earth is merely a common connection point that you can use if you want to. A lot of people want to, for various reasons. But it would also work to replace the earth with a nice thick copper wire, provided it was connected to everything the earth is. :)
Reference.
Everything’s relative, so it is used as a common reference point. Generally considered to be an object of sufficient size/charge capacity when compared to the circuit or body of interest; such that it serves as a charge-exchange medium where its net charge is considered to stay unchanged whe with respect to the circuit/body of interest.
Of all things, it is something I’m generally comfortable considering as charge-agnostic.
Here is an example of when it makes a difference: Hall Effect polarity.
Now let’s talk about magnetic poles… D:
There is a host of military equipment that runs on a negative voltages, the reason i was given by a military engineer is moving a large current through electrical components leads to problems with heat where as running a negative supply negates that issue. Ill admit it was a very long time and i’m probably butchering the explanation.
Positive and negative are just direction conventions– a negative supply is just a positive supply turned around. Do you remember any other details? Military electronics stuff is always interesting.
I have to wonder if he was speaking of motor vehicles where the chassis was connected to positive of the electrical system. i understand there where arguments as to way positive chassis connection was better, but most manufactures abandoned that convention decades ago Negative and positive voltages only exist in reference to a common potential.
I had a professor in physics who redefined everything to make it work with a left-hand rule instead of a right-hand. His iron-clad rationale? You could make the pointy-finger gesture and figure out cross products without putting your pencil down. A byproduct of this was rationalizing current with electron current.
Such people exist. It’s a high-wire act, if you ask me.
This is a non-issue; a complete and total crock.
Pick a system; use it. You’ll get the same results as the person using the other ‘standard’.
When you find an employer who will only hire people who learned “conventional” current flow, then articles such as this won’t be a crock. Not ’til then.
Learning based on electron flow makes the physics behind electronic components MUCH easier to understand. Conventional current is espoused mainly by people who soil their pants in fear at the phrase “left-hand rule”.
This is why all “free energy research” fail…
Floyd did version of his devices text in electron flow https://www.amazon.com/Electronic-Devices-Electron-Version-Technology/dp/0134420101/ref=dp_ob_title_bk
I gave away a copy a while back. Apparently now there is a PDF https://hristotrifonov.files.wordpress.com/2012/10/electronic-devices-9th-edition-by-floyd.pdf
When I entered tech school virtually TVs used vacuum tubes, as did much of the line powered entertainment equipment. Te only solid state equipment we seen come into the shop was Automotive 8 track player and and low end line powered radio/record player/8 track players units, as well as transistor table top broadcast radio sets.. Conventional current flow was briefly mentioned before thinking in terms of electron flow, because electron flow explained how circuits using vacuum tubes worked. Of course we eventually reached solid state devices and holes as current careers blew the minds of many students. To this day when I troubleshooting actual equipment or studying a schematic of a project I thing, and automatically deal with solid state device when they appear. I help conduch classes for those wanting to get the first ham radio license or want to upgrade, that’s one time when I have to consciously shift gears in my thinking. The other time when I’m talking shop or bench racing with those I know us the arrows to follow current flow in a circuit. Wit solid state being the rule I can’t blame them, but the grey beard has to help them navigate around any vacuum tube they run into, assuming they don’t run away from the higher voltage figures they see.
Well said. I came in slightly after you, having learned on both solid state and tube, then my career included more solid state than tube. I have no problem going back and forth between electron flow and “conventional” current flow.
Taking into account which way electrons move can be really misleading. An electrical circuit is not about the flow of electrons, in fact, we don’t even refer to electrons as flowing, but merely drifting. Electrons drift at a velocity of 0.2 mm/s. You could actually watch them move. Electrical signals of course move at a significant fraction of c, about 200,000,000mm/s.
While you may be technically accurate in the numerical values that you’ve listed, the idea that there’s is a definitive difference between flow and drift is a bit nebulous.
Think of the device known as “Newton’s Cradle.” The spheres on the inside barely move at all, yet the transference of energy is extremely fast between the two outer spheres. This demonstrates that the internal movement of the constituents of a system need not be in proportion to the speed at which a signal is transferred via them.
It shouldn’t be advocated that the current in an electrical circuit isn’t about the flow of elections. This implies that perhaps a current can flow with no movement of electrons (or any other chosen charge carrier.) When in fact, this “flow” is the very definition of current.
Current is a rate, so something must be changing with respect to time.
The transference of energy is the ultimate point of interest, which is determined by the net movement of the charge carriers.
…the flow of “elections”= electrons
*sheesh*
Conventional current is embedded into our electronic symbols and circuit simulators. Until we get new symbols and simulation tools, I’m sticking with the system 99.9% (estimate) of the world’s electrical engineers use.
I thought I would mention a few other conventions that have cause controversy.
Active v. Passive (Electrical Power)
SI units v. CGS units (EM Theory)
QWERTY v DVORAK (keyboard layout)
Metric units v English units (PCB layout)
Row variables vs Column variables (linear algebra)
1 indexed arrays v. 0 indexed arrays (programming)
Its a confusing and messy world we live in; Get used to it.