"Current" is not normally "electron current"
Hi Peter,
It seems to me you've got your wires crossed (no pun intended) and nobody much is exactly setting you completely straight on this.
It looks like you're repeatedly supposing that when people say "current", at least in terms of its
direction, they mean "flow of electrons". This is NOT the case. When people talk about the direction of current, assume they ALWAYS mean "conventional current" unless they say otherwise. Conventional current is the flow of "positive charge", and goes from the POSITIVE supply terminal to the NEGATIVE. It doesn't *MATTER* that (outside of electrolytes) there aren't really any mobile positive charges. That is what the convention is. 99% of the time you can forget all about the electrons.
If it helps, you can imagine there are really little positive charges flowing through the wires instead, the circuits won't mind as long as you don't tell anyone.
They didn't make this up to confuse you, or be bloody-minded. "Charge" has been known about for CENTURIES- capacitors for instance have their origins in the 18th-century *Leyden Jar*, and people have known about *static* electricity since Classical times :-O. After some point, experimenters figured out that there were two different types of "charge", whatever they were, that different methods of generating static produced one type or the other, and that the "charges" behaved in certain ways (opposite charges attract, and cancel each other out if they meet, and like charges repel each other). Now, maybe picture a conversation something like this:
A-Hello there B, what you got there?
B-Some "charges"! I've stored them in the jars using my electrophorus- as you can see, the electroscopes are showing their presence.
A-Oh yes, so they are! I guess. How come you've got two different jars?
B-Oh, you can't store different kinds in the same jar, they cancel each other out. One "subtracts" from the other, essentially.
A-There's different kinds? Oh. How do you remember which is which? I can't see anything apart from those "electroscopes" which look much the same to me.
B-Eh, well I've been thinking of naming them. I'm going to call the one that I get from rubbing silk on glass rods "positive", because it's a really positive experience, and uh, well the other type "subtracts" from the positive charge, so I'll call that "negative".
A-Rubbing silk on glass rods is a positive experience?
B-Not really, I made that up. But that's what I'm going to call them, anyway. And as current is the flow of charge, we shall say that it's specifically the flow of *positive* charge. That's a bit arbitary too, but we know that the direction of current makes a difference, so we might as well decide which charge's movement we're calling the current's "direction" so we can talk about it.
A-Hmm. Hey, shouldn't you wait for JJ Thompson to discover the electron?
B-HUH? NO! Go away. Fleming needs us to make a decision so he can tell what way round to point his fingers, and I'm not even sure if Thompson's been BORN yet.
A-Good point. What year IS this anyway? And who are we?
B-Sorry, I forget. I'm only allegorical anyway, or something.
May have been Benjamin Franklin, I'm not sure and it doesn't matter
. The electron has only been known about for slightly over 100 years now, and they'd already been doing a LOT of mucking about with electricity by then, the conventions have stuck and there is no real reason to change them other than to cause a lot of disruption.
As for the "charge carriers" part, note that in some media (p-type doped semiconductors), the current is strictly carried by POSITIVE-charged "holes" (the lack of electrons prevents the POSITIVE charges of the nuclei being cancelled out), and as j.p.bill there pointed out, current in electrolytes is carried by BOTH polarities of charge (ions, which genuinely exist in both types). So if you choose to interpret "current" as "direction that the charge carriers go in", then you have the situation where your version of "current" completely reverses direction repeatedly through most circuits, and through any electrolyte it is either "going both ways at once", or else you can consider it to have NO net flow! This is clearly *nonsense*. Current goes in one direction around a circuit, and components in series have the same current through them. The "flow of a specific polarity of charge" definition works that way where the "flow of charge carriers" one doesn't.
So I'll say again. Ignore what the "charge carriers" *REALLY* are, it makes no difference AFAIK outside of the realms of Hall-Effect devices (which you don't usually have to make yourself, even if you need one!!), and you should generally not need to care whether you have positive charges going one way, or negative charges going the other way, because for the majority of purposes it amounts to the same thing
. Hence yes, electron flow is from - to +, because electrons are negatively charged, and "current" is from + to -, because "current" refers to flow of POSITIVE charge.
As for the strange electrochemistry example, it could be that your teachers were describing the electron flow
inside the (battery) cell, where the situation is reversed. Remember the current flows in a CIRCLE in a circuit (ignoring parallel bits etc), that is where the name "circuit" comes from. The EMF of the cell is generated by the chemical reaction inside pulling electrons from the positive terminal and dumping them on the negative terminal, which is what makes them "positive" and "negative" in the first place. (It does this by positive ions going one way and negative ions going the other- again, TWO charge carriers in an electrolyte!)
Or it could simply be they were referring to conventional current outside the cell, and you got confused because you were thinking of "current" as meaning "flow of electrons". It's understandable you should be confused if nobody cleared that mistake up properly.
Well anyway, that was a lot longer than I'd have liked, but I hope it helped you or some random passer-by anyway!