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#128117 07/01/02 11:32 PM
Joined: May 2002
Posts: 68
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Eandrew Offline OP
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I know the electron theory states electrons move from negative to positive. But then I read that under this same theory, current flows from positive to negative. What?

#128118 07/02/02 06:34 AM
Joined: Oct 2000
Posts: 5,389
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Eandrew;
Scott had some good posts on this a while back.......i wish i could find them.

#128119 07/02/02 07:41 AM
Joined: Mar 2001
Posts: 2,056
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According to "The American Electricians Handbook"...
Although in most cases current consists of the actual motion of negative electricity in a certain direction, the conventional direction of a current is the direction in which positive electricity would move to cause the same effects as produced by the actual moton of electricity. Therefore, the direction of current, as it is usually considered, is in the opposite direction to the motion of the electrons.

Got that?!

#128120 07/02/02 01:44 PM
Joined: Oct 2001
Posts: 597
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The direction of current comes from the fluid theory of electricity first developed around 1600 AD. By 1700 AD the fluid was divided into special fluids, "vitreous" associated with electricity on glass-like substances, and "resinous" associated with electricity on amber, wax and rubber. Then in 1747, Ben Franklin arbitrarily assigned + and -. + to vitreous and - to resinous.

The "flow" of current was thought to go from + to -.

It wasn't until the idea of the atom at the beginning of the 20th century that the notion of "fluid" was replaced. Then electrons were thought of as marbles moving from - to +. This satisfied a lot of minds, until quantum physics of the post-Einstein world settled in. Electrons are now understood as packets of vibration with indistict edges (edges that blur off into infinity) that also have mass and motion.

In a conductor, such as copper, electrons move into the open places in the outer electron shell of the copper atoms. The electrons tend to stay in a small group of atoms, bouncing back and about, while the place that the electrons move into, the holes in the electron shell, actually is what flows as current. So, the holes move from + to - and we are back to Ben Franklin's arbitrary definition again.

You might say, current is the movement of nothing from + to -. [Linked Image]

There are more understandings coming.

What matters for us as electricians, IMHO, is that we understand the macro electromagnetic and electromechanical effects. Few of us have to get a logic state change to occur based on micro current flow through a few Angstroms of semiconductor material, with all its quantum realities.

The pre-Einstein model of negative charged electrons moving like marbles down a gutter works well for most people. When this model is connected with magnetic flux moving from North to South, all that is necessary is to consistantly apply the Left Hand Rules for EMF.

But, . . . just to balance this, [Linked Image] . . .if you want to use Ben Franklin's definition or the quantum physics definition of current, i.e., current flows from + to -, AND magnetic flux moves (this is the same as above) from North to South, all that is necessary is to consistantly apply the Right Hand Rules for EMF.

Consistency rules.

Al


The two "rule" links are to animated Quicktime gifs that take a bit to load, but illustrate the point.

[This message has been edited by ElectricAL (edited 07-02-2002).]


Al Hildenbrand
#128121 07/02/02 02:23 PM
Joined: Aug 2001
Posts: 7,520
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If you get into semiconductor theory, you'll find that it's full of holes!

No kidding, most theory was based on electrons moving one way, holes moving the other, and combining at the semiconductor junction.


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