direction of current ( was Earth's Magnetic Field)

[William Beaty <billb@ESKIMO.COM>]

On Tue, 11 May 1999, Chuck Britton wrote:

> Good example of opposite conventions being used.
> In this case of CURRENT it is important that we emphasis either the
> 'conventional' current of Ben Franklin (from positive to negative in
> external circuits) or the 'electron' current that seems to be
> stressed in High School Chemistry classes and not of anywhere else.

The "electron current" explanations that I've seen in articles aimed at
technicians seem to be MORE complicated than the ones using conventional
current.  An electron current is a flow of negative charge, therefor when
electrons flow forward, that is a current with a sign which is negative (a
vector pointing backwards as the charges move forwards.) When performing
ohm's-law operations on these numbers, the negative current moves
backwards towards the high-potential side of the circuit, and so the
negative signs cancel.  Why not just say that the current is positive in
the first place?  Are electron-conductors supposed to be more real than
positive carriers?

I'm convinced that this "negative current" stuff is misguided from the
start.  It is based on the misconception that wires are like hollow pipes.
Those who suffer from this misconception will put great emphasis on the
polarity of the charges and their initial point of origin.  The need for
"negative current is also based on the misconception that "electricity" is
a negative substance: the idea that only the negative charges have
mobility in any given conductor.  This is simply wrong.  But try telling
people that protons can flow.  According to their elementary textbooks,
electricity equals electrons, and protons are not electricity.  Yet in
electrolytic conductors and glowing gases, the current is an ion flow, and
it's a flow of positive charges in one direction and negative charges in
the other simultaneously.  When you stick your finger in a light socket,
there certainly is no "negative current"  flowing through your flesh!  In
integrated circuits we have a similar situation, with populations of
positive holes contributing non-trivial charge flows.  (But some would
argue that holes are "really" just electrons, so I'm not supposed to use
that example.)

If we were to build an entire complicated circuit from plastic hoses full
of salt water, or from glass tubes full of low-pressure neon, would this
cause the "negative current" people to suffer mental breakdowns?  :)   I
guess they would approve of circuits made from electron guns and charged
guide-electrodes in a vacuum, as long as we don't add any hydrogen to
create those nasty proton-currents that violate their backwards-rules.

In truth there are many different "kinds" of electric current.  Electron
flow in metallic conductors is just one of them.  And as Chuck points out,
even the metallic currents aren't conceptually "pure", because some metals
have valence-band hole mobility, and part of the current in those wires is
a flow of positive holes going in the "wrong" direction.  (Hey, is mercury
a hole-conductor?  It's a proton conductor since the positive ions are
free to move.) The "negative current" makes sense only if we focus
narrowly on our copper wires, and never look at the semiconductors or at
the wet insides of electrolytic capacitors or batteries (or even at the
hole-conductive zinc shells of some batteries.)

Conventional current is NOT only a convenient convention based on our
arbitrary assumption of positive charge carriers.  It also hides quite
nasty complexity.  "Negative current" is a miguided attempt to put the
complexity back in.  My trump card: ammeters measure conventional current,
not moving charges.  I.e. they ignore the electrons and holes and
multiply-charged, mixed-polarity ions going every which way, and they
instead assign a single simple number to the whole shebang.


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