Electron flow vs. current flow

by Stephanie Chasteen on June 30, 2012

I’ve written a previous post about how the direction of the flow of current in a circuit is opposite to the direction of electron flow in the circuit, due to historical anomalies.  A lot of people seem to get confused by this.  And I thought maybe this xkcd could help:

If only we could go back, that would avoid this whole confusion!

Here is the original post:

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.

 

Post to Twitter Post to Yahoo Buzz Post to Delicious Post to Digg Post to Facebook Post to Reddit Post to StumbleUpon

{ 5 comments… read them below or add one }

avatar Dallas Raby July 1, 2012 at 11:42 pm

I never knew that. It’s too late in life for me to stop picturing electrons and current flowing in the same direction, from negative to positive. Do you think that will be okay?

avatar Stephanie Chasteen July 2, 2012 at 12:45 am

As long as you don’t have to ever label the electron flow in a circuit diagram…. :-)

avatar Brian Lamore July 20, 2012 at 10:23 pm

This is how I intro the concept of hole flow: I have n students sit in a row of n+1 chairs. The empty chair is on one end. The students are modeling electrons in a metal/wire. I then have them shift one chair (flow) in the direction of the empty chair. When all are seated again, I ask them to notice where the empty chair is. (It’s on the other side.) I ask them how it got there. After a couple more shifts while paying attention to the empty chair, they can see the empty chair flowing opposite to their flow.

avatar Dan Weatherill August 11, 2012 at 7:10 pm

I’m sure this has been appreciated fully, but I think it’s also important to stress how useful it is to have conventional current, even if it’s perhaps ended up being defined the opposite way to how we historically might have chosen it (or is it the charge on the electron that got defined the wrong way? Or the sign convention of electrostatic potentials? Any one of which would sort out the confusion in this case…) .

Not all charge carriers in electrical systems are electrons. It is useful to have conventional current because it is the same direction irrespective of charge carriers. We may have e.g. hole current in a semiconductor, positive ion current in a fuel cell, or (more exotically) positron current etc etc. It would be rather an inconvenience in dealing with these things to have current flow suddenly switch directions.

I love this blog but have just discovered it :-D

DPW

avatar Bob December 19, 2013 at 10:49 pm

Here is a question for all: In any electric circuit, there is some resistance which will exhibit heating due to the I2R losses. Will ion flow through an electrolyte produce the same heating?

have fun

Bob

Leave a Comment

Previous post:

Next post: