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@contesting.com] On Behalf Of Jim Garland
Sent: Saturday, August 31, 2013 9:49 PM
To: 'Mike Waters'; amps@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@contesting.com] On Behalf Of Mike
> Waters
> Sent: Saturday, August 31, 2013 5:53 PM
> To: amps@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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