[Amps] Hole Flow

[Al Kozakiewicz]

Here's what it really boils down to:  I can't think of an electrical engineering problem (engineering, NOT physics) that requires understanding how current flows, or how active devices actually work.  Nor can I think of an electrical engineering problem where the sign of the current must match whatever definition of flow that floats your boat.  It's just math and device characteristics..  Taking transistors as one example, I could not explain with any real precision how they do what they do.  This has not stopped me from designing lots of switch and amplifier circuits in my lifetime.

Al
AB2ZY

-----Original Message-----
From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Jim Garland
Sent: Saturday, August 31, 2013 9:49 PM
To: 'Mike Waters'; amps at contesting.com
Subject: Re: [Amps] Hole Flow

This thread reminds me of the neverending debate about whether lightning jumps from the cloud to the ground, or from the ground to the cloud!  (I have heard it can go either way, depending on the type of cloud.)

 I agree that it's likely true the diode symbol grew out of a schematic representation of a cat's whisker detector. I found one website that affirms this possibility (http://en.wikipedia.org/wiki/Cat%27s-whisker_detector):
"The modern circuit symbol for a diode originated as a schematic drawing of a cat's-whisker detector."

However, when the cat's whisker detector was invented (roughly 1906)  the convention for electric current (flowing from plus to minus) had already been long established. In fact, the diode itself had been discovered roughly thirty years before either radio or the cat's whisker detector was invented.
The discoverer was a German physicist named Fernaned Braun, and the year was 1874. 

The word "electron" was coined by G. Johnstone Stoney in 1891, in experiments dealing with the passage of electric current through chemical solutions. The identification of the mysterious "electron" as a fundamental particle of nature is usually credited to J.J. Thomson, on the basis of experiments conducted in 1897. Interestingly, Thomson called these particles "corpuscles." Check out this interesting website on this early history, courtesy of the American Physical Society:
http://www.aip.org/history/electron/jjelectr.htm.

Well before any of these experiments, in 1861-62, the great Scottish physicist, James Clerk Maxwell formulated his famous four "Maxwell's Equations" that explained the relationship between charge, current, electric forces, and magnetic fields. As everybody knows, these four equations laid the groundwork for the discovery of electromagnetic waves. In Maxwell's formulation, a positive charge created an electric field which radiated outward from the charge. These so-called "lines of force" could terminate on a negative charge, or they could radiate outward forever.  

Implicit in Maxwell's Equations is the notion of electric current, from which one gets the sign convention that upsets some folks on this list.
Maxwell said that current (J) equals conductivity (sigma) multiplied by electric field (E). In his equations, the electric field always flows from positive to negative, and hence, so does current. Of course, nobody knew about the electron in those days, much less that it has a negative charge, so we shouldn't probably blame Mr. Maxwell for his sign convention. The important point, however, is that he was neither "right" nor "wrong." A "convention" is just an agreement that' is intended to avoid confusion and to keep everybody on the same page. It's no more right nor wrong than saying that "inches" are wrong and "centimeters" are right.

In any case, that's why in one of my earlier postings, I claimed that the convention was "universal." The convention goes back to the mid-19th century, and so far as I know nobody since then has tried to rewrite Maxwell's equations to make electric current flow from negative to positive.

That's not to say that some folks haven't found the convention troubling.
For instance, here' a comment from a Wikipedia discussion of the topic, in which the convention was blamed on engineers:
(http://www.allaboutcircuits.com/vol_3/chpt_3/1.html)

"Oddly enough, the direction of the diode symbol's "arrowhead" points against the direction of electron flow. This is because the diode symbol was invented by engineers, who predominantly use conventional flow notation in their schematics, showing current as a flow of charge from the positive (+) side of the voltage source to the negative (-). This convention holds true for all semiconductor symbols possessing "arrowheads:" the arrow points in the permitted direction of conventional flow, and against the permitted direction of electron flow."

Interestingly, the potential for confusion has diminished since the advent of semiconductor electronics. The modern trend is not to speak of what the actual particle carrying a charge is (electron, proton, ion, etc.) but just to speak of "charge carriers," with the understanding that they can be either positive or negative. In p-n diodes, for example, the charge carriers from the p-type region and the n-type region meet in the middle, annihilating each other and creating a depletion layer. 

In my case, I like the idea of thinking of current flowing from positive to negative, even though electrons in a vacuum tube go the other way.
Otherwise, when  I have a flashover in my HV power supply, I'd have to think of the arc jumping from the chassis up to the positive voltage, and that just seems strange!
\73,
Jiim W8ZR


> -----Original Message-----
> From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Mike 
> Waters
> Sent: Saturday, August 31, 2013 5:53 PM
> To: amps at contesting.com
> Subject: Re: [Amps] Hole Flow
> 
> > I was told years ago that the arrow represented the point in a point 
> > contact junction. The direction of current flow thing was added 
> > later
and
> > was just coincidence. True or not? Don't really know but I like the
story.
> > 73, Bill W6WRT
> 
> 
> I have never heard it explained any other way! At least not until this 
> thread.
> 


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