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.
>
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|