Why do electrons flow in a wire?

[ZapperZ]

Once again to justify positive current flow you must introduce layer about layer of complications. Why do I need any of that to understand that electrons flow from the negative terminal to the positive? This is simply the easiest and most effective way of teaching what needs to be taught. Keep in mind that the Navy, in a matter of a few weeks turns kids with a High School education into very capable technicians able to maintain and repair complex electronics which are essential to the defense of the nation.

Consider that it takes a community college 2 years to get to a similar point. (My total Navy classroom training lasted less then 6 months).

Yes, I did get some bad concepts from Navy training which had to be unlearned (perhaps more difficult, then if I was starting with a fresh slate) when I encountered a real E&M course.

Honestly, I don't mean to be difficult. But exactly where in such a class does a student actually DISCOVER that it is the electron that actually "flow"? A voltmeter, ammeter, etc, tells nothing on this. If you just say current flows from positive potential to negative potential of a battery, in what way as far as an electronics measurement goes, can a student contradict that? If one is ignorant of the band structure of a metal, where does one know that it is the conduction electron that actually "flows"?

And how does using the conventional current flow actually introduced layer and layer of complications? I think electrical engineers, of all people, are the ones who really do not care (or even believe?) in "electrons" and electron flow. Such details are irrelevant. So why would there be any conceptual difficulties in using the conventional definition of current?

Zz.

 

[Integral]

Once again, if you simply concentrate on WHAT IS HAPPENING it is simple, and cannot be to far wrong. The only incorrect concept was in the fundamental operation of inductors (the idea of a change in flux).

I am somewhat put off by your attitude because I have seen how effective Physics TAs are, or are NOT, is perhaps a better description. (I have a great deal more experience with them then most!) Yes, there is the occasional one that can and does teach something. So it is not clear to me why you are so against something that works. Your experience is with a system which treats teaching as a necessary evil. A distraction from your true goals which is research of one form or another.

The Navy on the other hand has a definite goal, to teach electronics, the resulting training is effective and meaningful. It is to bad that you cannot appreciate this, seems excess theory has clouded your vision of the rest of the world. Maxwell's concepts are essential at your level, they are not when you are on board ship and the radar is down.

 

[ZapperZ]

Once again, if you simply concentrate on WHAT IS HAPPENING it is simple, and cannot be to far wrong. The only incorrect concept was in the fundamental operation of inductors (the idea of a change in flux).

Sorry, but how do you know what is happening? How can you tell that it is an "electron flow" when you measure anything in a circuit? That is my question. If people who understand solid state physics don't tell you about conduction electrons, where exactly do you discover what exactly is "happening"? And what about those semiconductors that have positive holes as the majority charge carrier? What direction is the current flow there?

I am somewhat put off by your attitude because I have seen how effective Physics TAs are, or are NOT, is perhaps a better description. (I have a great deal more experience with them then most!) Yes, there is the occasional one that can and does teach something. So it is not clear to me why you are so against something that works. Your experience is with a system which treats teaching as a necessary evil. A distraction from your true goals which is research of one form or another.

But that is the same question that I asked you. Why are you so against something that works? The definition of current as adopted via convention WORKS! In fact, it is universally adopted, even with people who don't use English.

BTW, in what way is my "experience is with a system which treats teaching as a necessary evil"? Where did I convey such nasty position?

The Navy on the other hand has a definite goal, to teach electronics, the resulting training is effective and meaningful. It is to bad that you cannot appreciate this, seems excess theory has clouded your vision of the rest of the world. Maxwell's concepts are essential at your level, they are not when you are on board ship and the radar is down.

As an experimentalist, I care only in what has been demonstrated to work. So you will understand that I find it ironic of your accusation that "excess theory" has clouded my vision. I do not understand where the conventional definition of current would not work when a ship radar is down? 2 weeks ago I spent 4 days at the NRL. We spent time working on RF systems and pick-up antennaes. No where in such environment did I encounter problems with the electronics, or even communication with other engineers just because I adhere to the conventional definition of what current is. So please explain to me how adopting a conventional definition of current would not help in working and repairing a radar.

Zz.

 

[zoobyshoe]

The reason the concept of positive to negative current flow is confusing is because people are also taught that electrons flow from negative to positive:

hi - I am kinda barging in here but...
why does the current move in the opposite direction that the electrons are moving? that's what my book states, but it doesn't explain why. thanks!

Students are started off learning about static electricity: you rub electrons off one thing and leave atoms that are electron-hungry, so to speak on another. When electron rich things meet electron deficient things the electrons move from excess to deficiency.

Later, though, the confusion of positive current is thrown at you. Since this is really a relic of a more ignorant time, I agree with Integral it shouldn't be taught.

The fact no measuring device will reveal the actual direction of the current might be a case for ignoring the fact the convention is backward, except that the contradictions in the different stages of learning are unnecessarily confusing.

 

[chroot]

zooby,

The Hall effect will in fact demonstrate whether the moving charge carriers are positive or negative.

- Warren

 

[zoobyshoe]

zooby,

The Hall effect will in fact demonstrate whether the moving charge carriers are positive or negative.

- Warren

Right. I didnt phrase that well. I should have said "The fact that commonly used measuring devices don't reveal the direction of current flow might be a case for ignoring the fact the convention is backward, except that the contradictions in different stages of learning are unnescesarily confusing."

 

[BobG]

hi - I am kinda barging in here but...
why does the current move in the opposite direction that the electrons are moving? that's what my book states, but it doesn't explain why. thanks!

My first training in electricity was very similar to Integral's - almost identical, except for one key point. My training was vastly superior to Integral's because it was given by the Air Force instead of the Navy.

There is actually a very good reason for the discrepancy.

How fast does electricity move? In other words, from the time you flick the light switch, how long does it take for the light to turn on?

How fast do the electrons move? In other words, from the time you crank your starter, how long does it take for an electron to move from the battery to the starter?

I was once told it takes about three days for an electron to move from the battery terminal to the starter (plus or minus depending upon how long the cable is). I've never actually checked that, since it is kind of irrelevant. But, the point is that the speed of electricity and the speed of electron movement aren't exactly the same thing.

It's more like a bunch of students sitting at a row of desks with the back desk empty. If you have 10 seats in the row, and the student at desk #9 moves back one seat, the 'hole' has moved up one seat. Student at desk #8 moves back, the 'hole' moves up one. And so on and so on. The end result is that , over certain amount of time, the 'current' has moved the entire length of the row, while each 'electron' has only moved one desk.

The 'effect' of electricity is moving one direction while the 'cause' is moving the opposite.

 

[zoobyshoe]

No. Drift velocity and the speed of the emf is a different can of worms. Not the same as the direction of current flow. The fact that the actual physical progress of the electrons is much slower than the impulse of power they produce down the whole line when they move is a separate issue.


The discrepancy in the direction of current arises, pure and simply, from a time when no one knew which direction the current flowed and took a stab at a guess:

"...Electrons can now flow through the complete circuit; however we usually visualize a flow of positive charges in the opposite direction and call that the current. Thus we use this imaginary positive current for purposes of circuit analysis, keeping in mind that the true current is largely that of electrons, and in the opposite direction."

-Physics Concepts and Consequences
Raymond L. Murray
Grover C. Cobb
©1970 by Prentice-Hall, Inc.,Englewood Cliffs, N.J.
Library of Congress :79-118661

I don't believe the concept of "positive hole flow" came into use till the invention of semi-conductor devices, when someone decided it would be a useful tool to understand how these work.

 

[Math Is Hard]

I was once told it takes about three days for an electron to move from the battery terminal to the starter (plus or minus depending upon how long the cable is). I've never actually checked that, since it is kind of irrelevant. But, the point is that the speed of electricity and the speed of electron movement aren't exactly the same thing.

They're not?? I had no idea.

The end result is that , over certain amount of time, the 'current' has moved the entire length of the row, while each 'electron' has only moved one desk.

The 'effect' of electricity is moving one direction while the 'cause' is moving the opposite.

Oh -I think I see what you mean now. Clever analogy!

 

[Integral]

My first training in electricity was very similar to Integral's - almost identical, except for one key point. My training was vastly superior to Integral's because it was given by the Air Force instead of the Navy.

This is a whole different topic for debate! Flyboy :yuck: