Electron flow vs current flow? (Repost)

by Stephanie Chasteen on September 1, 2011

The geekgirl is going a little nutty over here, hence the silence on the posting front.  I’ve got a good excuse — I’m getting married in about 10 days.  So cut a girl some slack.  🙂  Fun facts — we’re getting married on 9/10/11 — which only happens 11 times in every 100 years, and the next two years (10/11/12, 11/12/13) are the only such dates for another 90-something years.  How cool is that?  Our officiant is my old mentor Paul Doherty from the Exploratorium, and he’s doing something involving liquid nitrogen for the pre-wedding BBQ, and reading from Richard Feynman for the ceremony.  So, two weeks from now, I’ll be covalently bonded to my sweetheart.  One friend put it, “you’ll be Mrs. Geekgirl.”  Hmm, I think that actually makes my sweetie Mr. Geekgirl, doesn’t it?  🙂

So, because I’m a bit too crazed to write something new, I’m reposting an oldie but goodie, describing the difference between electron flow and current flow.  The original post has a VERY rich string of comments — check it out for more on this confusing topic!

——–

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.

Why are we cursed with this convention?  Here’s a relevant comic from xkcd

{ 6 comments… read them below or add one }

Carrie Fitzgerald September 1, 2011 at 4:18 am

Congratulations! 🙂

Will Robinson November 23, 2011 at 6:39 pm

Stephanie, thanks for the explanation. I’m wondering about the sentence, “And electrons do get pulled towards the negative charge, like you say.” 8th grade teacher mentioned “…towards the opposite charge.” Shouldn’t the explanation have said that electrons get pulled towards the positive charge (i.e., from the negative pole to the positive pole)?

But I’m trying to get my arms around another concept: I’ve been told that, in a copper wire, individual electrons are actually traveling at about walking speed. I’m trying to figure out what the relationship is between current and actual electron transference between atoms. Is there also transference of energy from one electron to another along a wire in addition to actual movement of the electrons (i.e., electrons transferring their excited state opposite the direction of the current without actually moving on a macro scale)? I guess this implies that there would be two mechanisms of energy transference: energy movement, and electron movement (along a wire). Or is the current derived solely from electrons moving through the wire?

Thanks.

Stephanie Chasteen November 23, 2011 at 8:45 pm

Hi Will,

Thanks for noticing that typo — I’m amazed nobody else pointed it out with all the comments on previous versions of that post. It all gets so confusing.

From my understanding, current is derived solely from electrons moving through the wire, though there are almost certainly some complicated effects as well which are beyond the scope of what you’re asking about. Yes, electrons travel at about walking speed. You can see this nicely in the PhET simulation on current at http://phet.colorado.edu. Those blue balls represent the electrons, and each one “nudges” the next one along. This results in a net flow of charge into and out of the circuit, even though one individual electron doesn’t make the complete round of the circuit very quickly. That’s probably the best place for you to get an accurate visual of this.
All those electrons that are moving are the conduction electrons, which have more or less the same energy, so transferrence of the excited state from one electron to the other — while possible — isn’t likely to make a big difference. But it’s possible that there’s something that I’m unaware of.

isaac March 21, 2015 at 3:30 pm

thanks it was helpfull

Deepak Maurya June 23, 2015 at 1:38 am

Electron conductor me ek place se other place par jane se current flow hota hai ?,please tell me

Mohammmad Saad Ansari October 15, 2015 at 2:59 pm

FLOW OF CURRENT IN CHARGING MODE:
Anode to Cathode (+) pole to (-) pole
ELECTRON FLOW:
Cathode to Anode (-) pole to (+) pole

FLOW OF CURRENT IN DISCHARGING MODE:
Cathode to Anode (-) pole to (+) pole
ELECTRON FLOW
Anode to Cathode (+) pole to (-) pole

Got it? Try understanding everything simply.

Because…

“If you can’t explain it simply, you don’t understand it well enough”
— Albert Einstein

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