Current Flow and electron flow direction

[raghavv]

Dear Sir/Madam,

Why is the current flow in any circuits or in general, indicated opposite to the direction of motion of electron even though the flow of electrons is the one responsible for the current.

Thanks,
Raghav

[Clanad]

Our friends at Wikipedia explain it in a lot fewer words than I could...

"In metallic solids, electricity flows by means of electrons, from lower to higher electrical potential. In other media, any stream of charged objects may constitute an electric current. To provide a definition of current that is independent of the type of charge carriers flowing, conventional current is defined to flow in the same direction as positive charges. So in metals where the charge carriers (electrons) are negative, conventional current flows in the opposite direction as the electrons. In conductors where the charge carriers are positive, conventional current flows in the same direction as the charge carriers."

[Hymie]

My college lecturers said that the early pioneers (of electrical engineering) chose the current flow direction arbitrarily, as flowing from a positive voltage to a negative (or lower) voltage – as they had no way of determining the actual direction of current flow.

When physics developed to where the direction of electron flow could be determined, it was Sods Law that they had picked the wrong direction of current flow.

So by convention, current flows from positive to negative, in reality electrons flow (electron flow) from negative to positive.

[Are you certain these are not home/course work questions?]

[chakka35]

Hymie is exactly right. I have always maintained that the advent of transistors was the right time to correct that ancient mistake. You can explain how a transistor works very satisfactorily by showing the flow of electrons, and then you have to say, lamely, that the arrow in the elctron symbol points in the wrong direction, but that we have to put up with it.

In what conductors, Clanad, do positive ions form the current flow and what happens to the electrons they have left floating behind with nothing to orbit around? Not a challenge, a question - because I'm puzzled.

[mibn2cweus]

Current flow is not exclusive to electron flow. Electrical currents flow both ways! There are potentially (pun intended) both positive (ionic) and negative (electron) currents flowing in a conductive circuit.

http://amasci.com/miscon/eleca.html#frkel

[Old_Geezer]

My suspicion is that in the early days no one knew what was flowing where, so plumped for positive to negative current flow. Later they realised it was electrons going from negative to positive but by then it was too late and too embarassing to correct everything. So they made up excuses about hole flow and stuff like that. At least I've not seen anything to prove that incorrect.

[Old_Geezer]

Oh right, more or less what Hymie said.

[mibn2cweus]

Electrons have a negative charge thus are attracted to a positive charge. Foe a given polarity of charge, current will flow in one direction or the other or both depending on the nature of the charge carriers within the conductive material in the circuit.

Let's face the facts here. The reason behind the disagreement and the ensuing confusion arose because technicians and engineers are inherently at odds with each other and like to butt heads! Opposites attract. ;o)

[Clanad]

Chakka... although outside of my area of expertise, I recall (and confirm after consulitng my yellowing and dogearred college physics book) that an electric current his is typically carried by moving electrons in a conductor such as wire. It can also be carried by ions in an electrolyte, or by both ions and electrons in a plasma. So, if my lightning (pun warning) fast brain is correctly interpreting your question, the answer would be "electrolyte".
As to the spare electrons left... just trying not to bump into each other would be my guess!

[chakka35]

Quite right, Clanad. If you were to ionise a gas then the positive ions would be as free to move towards the negative pole as the electrons towards the positive. I concerned myself too much with solid conductors.

I am mystified by the idea that the mistake in naming the direction of current flow in solid conductors and semiconductors was too difficult or embarrassing to make. What about all those other changes in our textbooks? Cycles per second to Hertz, condensers and coils to capacitors and inductors, centrifugal force to centripetal (neither of which exists) and the wholesale adoption of metric and SI units where British (once called Imperial) sometimes ruled before.
If all textbooks had changed after, say, 1950 we wouldn't be having this conversation now.

[Hymie]

I believe that it was sometime around the 1920s that the direction of electron flow was determined. So why did the convention of indicating the direction of current flow not change at that time?

I can only think ‘the powers that be’ decided that it would cause confusion and that it was somewhat academic as to the actual direction of electron flow. After all, it is standard practice to indicate a current flow direction on an ac mains circuit from Live to Neutral (where the direction of current flow is changing 50 times a second – or should that be 100 times).

It is interesting that the symbols used for early semiconductor devices (bipolar transistors, diodes etc) employ conventional current flow direction, whereas the direction arrows on later devices (FET transistors etc) follow electron flow – all very confusing for the novice.

[heathfield]

I remember being shown an article in ''Wireless World'' magazine from as late as 1928, where the theory of electron flow in a thermionic valve was explained. The heated cathode released negatively charged electrons. These were drawn toward the positively charged anode to produce a current flow. The magazine editorial said the theory was interesting, and wondered if and when it would ever be proved to be correct!