Electron flow vs. current flow

by Stephanie Chasteen on February 27, 2009

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 positive 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

{ 50 comments }

Kenneth Finnegan February 27, 2009 at 8:15 pm

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.

Stacy Kissel March 7, 2009 at 1:51 am

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.

sciencegeekgirl March 8, 2009 at 3:58 pm

Thanks, Stacy, for the history note!

By the way, I happen to be one of the CPO writers.

I’ve been wracking my brain and am pulling a blank — what does CPO stand for?

sciencegeekgirl March 10, 2009 at 5:08 am

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

David E Darragh March 20, 2009 at 8:17 pm

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

sciencegeekgirl March 25, 2009 at 4:58 pm

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?

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).

chetan kumar December 7, 2009 at 9:12 am

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.

chetan kumar December 7, 2009 at 9:14 am

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.

swati January 8, 2010 at 8:34 am

Thanks, that was very useful.

I got confused too!

siddharth February 19, 2010 at 12:57 pm

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….

siddharth February 19, 2010 at 1:03 pm

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….

Bellatrix Bly March 1, 2010 at 9:38 pm

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!

Jojo Bizarro June 17, 2010 at 5:23 am

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.

Anurag Mishra June 17, 2010 at 2:16 pm

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?
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).

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.

Anurag Mishra June 17, 2010 at 2:31 pm

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.

sciencegeekgirl June 17, 2010 at 3:41 pm

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…. 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.

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.

Glenn travis December 7, 2010 at 4:23 am

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.

Glenn travis December 7, 2010 at 4:30 am

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.
;^)

Glenn travis December 7, 2010 at 4:46 am

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

Glenn travis December 7, 2010 at 4:53 am

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.

shashank tyagi May 19, 2011 at 5:16 am

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.

kodimela lakshmana rao August 26, 2011 at 3:51 am

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????????

Stephanie Chasteen August 26, 2011 at 1:44 pm

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!

mawella September 4, 2011 at 7:20 pm

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 :PP;p he he 😛

JonnyBravo September 8, 2011 at 4:38 am

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?

Stephanie Chasteen September 8, 2011 at 5:23 pm

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.

JonnyBravo September 9, 2011 at 3:39 am

“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?

JonnyBravo September 9, 2011 at 3:51 am

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 😮

JonnyBravo September 9, 2011 at 3:55 am

.. Just say no to Franklinian Flow

JonnyBravo September 9, 2011 at 4:01 am

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.

Stephanie Chasteen September 9, 2011 at 4:13 am

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!!

JonnyBravo September 9, 2011 at 4:22 am

So why do they keep the idea of Franklin current? how does it help anything?

Stephanie Chasteen September 9, 2011 at 4:57 am

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.”)

maansingh February 17, 2012 at 8:42 am

current flow from generator to load how electron move or pulsing .if electron move one point to other point then metal is Detroit with time due to electron loss. But it is not . please clarify my Que.

ebrahim tajary February 23, 2012 at 9:56 am

i am teacher physics

Keith Waggoner March 24, 2012 at 2:04 am

In the fields of physics, and nuclear and radiological engineering, electrons are called beta particles. Cathode rays are called beta radiation. What science teachers call electron, older electronics techs call cathode rays, and RadCon techs call beta radiation. A beta explodes out of a neutron during radioactive decay at about 20% light speed, 33 million mph. The neutron has lost its negative charge, but still has its positive charge; it has become a proton. Beta radiation causes cataract. Betas from tritium in gauges and emergency signs perform the same function that cathode rays play in an old style TV tube by energizing light emitting phosphors.

McBrain Miller April 17, 2012 at 7:50 am

What is the quikest way to troubleshoot a tv?

KAUSHLENDRA PANDEY April 17, 2012 at 5:09 pm

why the current flows opposite direction to the flow of ELECTRON

KAUSHLENDRA PANDEY April 17, 2012 at 5:11 pm

s?

Krushna Roy May 23, 2012 at 7:14 am

Hi,
We know that the direction of flow of current is opposite the direction of flow of electron. But my question is why it is opposite? Why not the direction of flow of electron is the direction of current?
Is there any specific reason?
In case of a voltage source (higher-lower potential), the terminals have the equal amount of charge quantities (positive/negative). So why positive is higher potential pole and negative is lower potential pole?

If anybody have a clear concept then please give your comment.

Stephanie Chasteen May 23, 2012 at 3:33 pm

Hi Krushna,

It’s simply a historical anomaly, no particular reason. Stacey above described the history:

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

Stephanie

surabhi gupta July 8, 2012 at 2:41 am

MAANSINGH…
electrons do not move from one point to another, they just vibrate ,,, so it is the energy that flows……. so no lass of electron.

Stephanie Chasteen July 8, 2012 at 3:23 pm

Nonsense. Look up “drift velocity”. Electrons do move.

Priya July 25, 2012 at 12:11 pm

does electron flow in metals means that the electrons are displaced from one atom to the other?

Stephanie Chasteen July 25, 2012 at 2:33 pm

In a metal the electrons aren’t really bound to any one atom anymore, they’re called an “electron sea”. So it’s not so much displacement from one atom to the next, as just that there is this big sloshy mix of electrons due to all the atoms and they can flow around. Those are the outermost “conduction” electrons. There are also “valence” electrons, which are still bound to the individual atoms.

birendra bahadur singh July 29, 2012 at 4:34 pm

i think it is the conventional flow of current which flows from +ve to -ve terminal of a battery and electrons flow from opposite direction because they have tendency to flow from lower to higher potential.

birendra bahadur singh July 29, 2012 at 4:46 pm

the current is not due to the flow of charged particles but due to flow of particularly directed electron flow.since the electrons in metallic conductors are loosely bound to atom,they can be easily attracted toward positive terminal of supply or battery and this current of electrons in definite direction makes of electric current as water in river makes water current.

shubham August 17, 2012 at 4:05 pm

hey guys……….
thanks for giving me these useful notes.
love you all………………………………………………

Weylin September 18, 2012 at 2:22 am

This is nonsense.

Current does not “flow”. Charges flow.
Current and Voltage are not two separate entities.
Current is the volume, and voltage is the force, and there is a mathematical relationship between those two attributes.

If it’s a solid such as metal, then the charges (which in this case are comprised of electrons) flow to the positive.
If it’s a liquid, then you may very likely have electrons and positive ions flowing in opposite directions, with those positive ions depositing themselves onto the negative source, which I’m pretty sure is the entire process behind electroplating.

Textbooks need to get this right, or they’re just going to confuse the hell out of everyone. I’m STILL trying to recover from all the misinformation shoved down my throat when i was younger.

Rodger September 29, 2012 at 11:34 am

I’m fairly new to the study of electricity in detail, so please excuse my ignorance. When we start talking about the use of diodes or transistors (essentially one way switches) in circuits and the reality of electron flow vs current, doesn’t the placement of these one way switches change depending on which model you use? In water line design, for instance, the placement of check valves is very dependent upon the direction of flow of the water.

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