I just got this question from a teacher on Webconnect (which lets teachers ask science questions):
“In the past when I taught electricity I always understood that it flows from the negative terminal to the positive. The CPO books and materials have the opposite – from positive to negative. This doesn’t make sense to me in how you generate the flow of electrons, pulling to the opposite charge. Is the book wrong or have I forgotten stuff? 8th grade teacher”
It depends on what you define as “electricity”. Do you mean the flow of “electrons” or the flow of “current”? Because, due to an unfortunate quirk of history, the direction of *current* flow is opposite to the direction of *electron* flow. Take a moment and re-read that, because it’s not what you would expect. If electrons are flowing to the right across this screen, then we say that current is flowing to the left.
So, let’s say that the left hand side of this screen is the positive terminal and the right hand side is the negative terminal
+ -
*Electrons* will flow towards the opposite charge, as you say. That’s which direction? Right to left
<—- electrons
But *current* is the opposite direction. Left to right.
—-> current
So *current* does flow from positive to negative, like your books say. And electrons do get pulled towards the negative charge, like you say. But we define electric current to be the opposite direction of electron flow.
There’s some good history on why it’s defined this way, but I’m too busy to find it right now — if someone has a good link, stick it in the comments, thanks!
UPDATE 4/27
Here’s a relevant comic from xkcd
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{ 33 comments… read them below or add one }
Another thing to note is that the speed of current is dependent on the speed of the electric field, which is C (3E8 m/s), where the speed of the electrons is based on the current density (current per area of wire). The “drift velocity” of the electrons ends up being mind-blowingly slow: normal household values run in the range of 0.15 mm/s.
We can blame Ben Franklin for this one. He coined the terms positive and negative and named the charges that move from object to object positive. It wasn’t until much later that we discovered electrons are what move in solids. See http://www.allaboutcircuits.com/vol_1/chpt_1/7.html Students get a kick out of learning that our definition of current in circuits is backward! By the way, I happen to be one of the CPO writers.
Thanks, Stacy, for the history note!
I’ve been wracking my brain and am pulling a blank — what does CPO stand for?
And Chemgeek sent me another history link from NASA about Franklin and the twisted route of history: http://www-istp.gsfc.nasa.gov/Education/woppos.html
Okay, now, in welding, we can change polarity. DCEN is referred to as “straight polarity.” (work positive, electrode negative) DCEP, or “reverse polarity” is work piece negative, electrode positve. Which direction(s) are the electrons and current flowing? Now, I’m really confused.
Dave
The direction would depend on the polarity. Electrons always go from negative to positive (and current from positive to negative). If you’ve “reversed polarity” then all you’ve done is switch + and -, and then the electrons (and current) will switch direction. In my fancy schmancy diagram in the post above, that would amount to switching the + and -, so electrons will now flow to the right.
In other words, in DCEN your electrons are flowing away from the electrode (and current towards the electrode) and in DCEP the electrons are flowing towards the electrode (and current away from the electrode).
we can that current flows from positive to negative because of current flows from higher potential to lower potential so that we that current flows from positive to negative.
we can that current flows from positive to negative because of current flows from higher potential to lower potential so that we may say that current flows from positive to negative.
Thanks, that was very useful.
I got confused too!
actually it is a just a game of energy….
look….we know opposite charges cant stay apart ..this is wat was founded naturally…so if ++++++ (–>>>>>>>) ——-
charges r separated…so assume potential diff between.these be ‘V’..after some time say ‘t’situation will be..+++ (–>>>>>) — … now potential has dropped to say ‘v’..
beacuse most of -ve electrons have gone to +ve side..to decrease the energy of system..(that is the law..they try to come to each other to decrease the energy of system ..of each other..)…so to derive a mathematical equation for this..we gave a convention first that +ve side will be treated as higher potential and -ve side low potential….so v(+)-v(-) is a +ve quantity…and this difference is found to be proportional to resistance and flow of current…now resistance is +ve thing(because hindrance to flow is +ve thing)…..so current is given +ve thing…
so when we go from…v(+) to v(-)……we consider something going from ++ (–>>>>) –….so in an eq.. both sides must be +ve…thats y a convention was set that current flows from ++ to — direction..it was just a convention set up during its invention..so that w can study it mathematically…and after that every thin was set according to this convention…every law is studied lik that…books were written in this way…so mits just a convention…and its just an abstract thing….ok…got the point….just a convention…nothin real..in it…in reality its just the electron which flow nothin else….
we want the equation….v(+)-v(-).. be +ve must be +ve thing…so in an equation….we relate it with product of resistance(a +ve thing) and cuurent(must be +ve)…so current is given convention from ++ terminal to — terminal….
Ohmigawd, thanks! I’ve been having a bad day, and science class didn’t make it any better, so I think you’ve just saved my sanity!
Given that electrons flow from negative to positive, and that electrons are only things that move along the entire current path, it should make perfect sense that electric current flows from negative to positive. We say that the Danube River flows eastward out of Germany and into the Black Sea because the carriers of that flow, water molecules, go that way. To say that the Danube flows westward out of the Black Sea and into Germany sounds downright absurd, and to say that current flows from positive to negative sounds equally idiotic. Whenever I see current arrows going from positive to negative on a diagram, I can’t help but think that whoever drew them is ignorant.
Well, this is a simple fundamental why DCEP is called reverse polarity and DCEN is called straight polarity. In the case of DCEN, the electrons are flowing from the electrode to the workpiece being welded and the flow of weld metal is also from the electrode (or filler wire) to the workpiece, hence straight polarity. In the case of DCEP, flow of electrons is from the workpiece to the electrode while the flow of weld metal is from the electrode (or filler wire) to the workpiece, hence reverse polarity. Further approximately 70% of the heat is generated at the positive side. This is the reason why we get faster welding while using DCEP.
I do agree to Siddharth. A current is defined as the flow, be it a flow of river or flow of electrons! Whenever there is difference in the quantum of charge, there will be a resultant flow from the higher side to lower side. Ofcourse, after overcoming the barriers. (Imagine the case of lightening, there is always charge in the clouds, but lightening occurs only when it has sufficient potential difference to overcome the resistance provided by the atmosphere) So, if there is an accumulation of 10000+ charges at one side and 100+ on the other side, there will be a flow from the 10000 side to 100 side. This was the thing taken into consideration when the current was defined. Further, there is nothing in this world so-called NON CONDUCTOR. A material may be called as a BAD CONDUCTOR of electricity, but it cannot be called as NON CONDUCTOR. These are called bad conductors because they provide resistance to the current flow and that resistance has a limit, that is, the material can withstand certain amount of potential difference until it gives way. That is why for working on very high voltage equipment we need thicker rubber mat to stand on, rather than a thinner rubber mat which would have been sufficient for low voltage. Another thing, every material becomes a super-conductor at absolute zero, that is 0 Kelvin. This means that at zero Kelvin, there is no resistance to the flow of electrons.
You’re calling all physicists ignorant?
Unfortunately, even though it seems to make so much sense that current should go from negative to positive, since that’s the direction of electron flow, the convention that current flows from positive to negative was created by Franklin, long before we knew what the charge carriers were (or, in your example, before we could see the water molecules in the Danube — or, even, the direction of the flow of the water. All we knew was that the “Danube” would turn a flywheel, but didn’t know which way it was moving to do so). So, even though it’s counter-intuitive, we’re stuck with the convention. The way that current is shown on current diagrams is opposite to the direction of electron flow. It’s a quirk of history, rather than that we don’t know what we’re doing.
It sounds like someone or physicist or textbook authors or Postgraduate just had to throw a monkey wrench into things rather than letting Ben lay. You know, “look at me, I can throw a confusion factor into circuit study!” Once things had been discovered, and defined more clearly say atoms, and electrons; why leave Ben’s notion/definition in things any longer? Do we say that the Sun orbits the Earth for example?
I learned electron current flow ‘theory’ when I took a Bell & Howell course way back in ought and 76. They even taught it to Navy Nuclear designated Machinist Mates in ought and 68 at A school.
Just what does this so called “current flow” accomplish?
What does it add, except an archaic confusion factor. Why not simply say current flow is electron flow (forget holes for now). As far as I am concerned, any author or program that “preaches” current flow is not trying to teach or help, they are just showing off their irrelevant, confusing knowledge.
It’s high time to drop the old “current flow”. Let it die at last.
With regard to physicists; when I was at the nuclear reactor trainer in Virginia years ago, I discussed Things that I saw happen in our core with the them. They refused to believe it even after I showed them the charts. Of course they were theoretical physists. We were convinced that they has to keep lead in their pockets to keep from floating off the ground.
;^)
Now back to the dreaded term POTENTIAL. Now that is relative when it comes to discussing charge, and just whom’s convection. Again V+ has nothing to do with a higher potential does V- , it’s just a way of looking at things.
In electron flow V- just means that is where are where all the electrons are, hence it has a negative charge, relative to the terminal of the voltage supply.
Now in Conventional flow, V+ means again that is where the electrons are; however; the + indicates that there are more or a surplus of electrons than
at the other terminal of the voltage supply
Re: welding, just go along with what you learn at welding school. It worked for me when I was at Ships Emergency Welder School in Uncle Sam’s Canoe Club.
The electric current is defined as the rate of flow of charges and not the electrons.
i=dq/dt
so if we define direction of electric current in the direction of electrons flow,current becomes negative because charges on electrons are negative.
example: if an electron moves from one end to another in 2 seconds
current = charge flow/time taken
= – (1.6*10^-19)/2
Therefore to make the current a positive quantity,it is defined as opposite to the electrons flow.
Suppose if we take a river,in that if water molecules move from north to south then we say that river is flowing from north to south direction,but in our discussion we are saying if electrons are moving in one direction but the current is moving in another direction.How is it possible????????
Kodimela,
That’s a great analogy, and shows why this is such a confusing idea. In your analogy, however, the water molecules are the positive charges, not the electrons. Imagine that there is a fish in the water, too, which needs to swim upstream to spawn. So, the fish necessarily moves in the opposite direction from the current. The fish are like the electrons. It’s just that we didn’t realize the fish/electrons were there when we first talked about the current and so we defined the flow in the wrong way!
yahhhh finally!! this were usefull!! ;;P me and my frd were fighting for direction of current flow :p;p and finally this gave the anser
he he ;p;p but still v are hving separate ideas!! but when comes to calculation answer are some 
P;p he he 
So to recap what I have picked up from this debate is this:
Electrons flow from the negative terminal towards the positive terminal. Neg -> -> -> -> Pos Thus this is the flow of the current. Neg to Pos.
However when Franklin came up with the method of mapping out this flow. IE: writing schematics. He deemed since the Electrons Start at one point and move to the other point. Then starting point should be illustrated as Positive.
Am I correct?
So when I go online and look at a diagram of how to hook a battery to a fan. Where the the diagram says +Pos. It really means the Negatively charged terminal/Starting point of the flow of electrons?
Johnny Bravo,
No, not quite. Current is *defined* as being the *opposite* of the direction of the flow of electrons. So when you say:
“Electrons flow from the negative terminal towards the positive terminal. Neg -> -> -> -> Pos Thus this is the flow of the current. Neg to Pos. ”
…that’s not correct. Electrons flow from the negative terminal to the positive terminal, so the flow of electrons is from negative to positive terminal, so the flow of CURRENT is from POSITIVE to NEGATIVE.
Franklin just had the sign of the charge carrier wrong. If positive particles moved instead of negative particles, then the flow of those particles would be the same direction as the flow of the current. He wasn’t trying to figure out whether electrons were moving or not, he just knew something was moving from one side of the circuit to the other, and he happened to pick the wrong thing.
None of this changes how you would interpret a diagram hooking a battery to the fan. Negative is still negative, positive is still positive. So, where the diagram says +positive, that REALLY IS positive. It’s the ending point of the electrons.
All this matters only for physicists and physics students — it doesn’t change how wiring diagrams are interpreted.
“Franklin just had the sign of the charge carrier wrong”
So if he had chosen the – neg. to be the starting point. Then today we would say the current flows from neg to pos?
As said before. Knowing that the earth revolves around the sun. But for the sake of oldtimers and some old time methods of astronomy we will just humor them and keep the notion that sun revolves around earth.
I gather that conventional current flow is an out dated theory that needs to be replaced.
“None of this changes how you would interpret a diagram hooking a battery to the fan. Negative is still negative, positive is still positive. So, where the diagram says +positive, that REALLY IS positive. It’s the ending point of the electrons. ”
Well now my fan will spin in the opposite direction then I want it to :p Unless of course they have been labeling batteries with this backwards format as well
.. Just say no to Franklinian Flow
Sorry to blow up the board but Im just really into this. I guess it doesn’t really matter when using the schematics since positive charge flowing forwards is equivalent to negative charge flowing backwards…… even though there is no positive charge moving.
I think I have a touch of OCD and it just drives me crazy know that neg electrons are the only thing actually moving around the circuit.
Johnny,
You say: I guess it doesn’t really matter when using the schematics since positive charge flowing forwards is equivalent to negative charge flowing backwards…… even though there is no positive charge moving.
Yes, that’s exactly right!!
So why do they keep the idea of Franklin current? how does it help anything?
It’s hard to break convention… all the textbooks and diagrams and everything use “conventional current” (which is what you’re talking about as “Franklin current.”)