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On Fri, 8 Jan 1999, Darrell Wyatt wrote:
First of all, I don't want to lend the impression that I am a
know-it-all. I also have a degree in electrical engineering, and the
information I received was somewhat different than that which was
presented in reference to "which way does electricity flow?". That is
NOT to say that my information was correct...only different. I was
taught that electrons flowed from negative to positive, and that there
were valence band "holes" left by these flowing electrons which
represented the lack of
Hi Darrell! Me too, I'm frequently wrong too. That's why I aim most of
my writing at the 6th-grade level and below. It's lots easier to maintain
the levels of detail demanded by grade school than it is to do the same at
the levels demanded of professional physics.
I think you're correct: holes, and the valence band current they make
possible, do exist in semiconductors, and in a few exotic metals, but not
in copper, aluminum, iron, etc. I think Bismuth has major hole flow. I
might be wrong, and perhaps there is a small percentage of holes even in
copper, etc. This would be a good question for the PHYS-L discussion
list.
From what I understand about semiconductor physics, the valence band and
conduction band are overlapped, so conductivity is large even if no energy
is used to boost valence-band electrons up to the conduction band. More
importantly, the valence band of metals is entirely filled, and even the
conduction band is almost filled. Therefor, "normal" metals conduct
because of free electrons located at the top of the conduction band. A
simplified discussion about conductivity wouldn't discuss all of the
abnormal types of charge flow. However, since I'm trying to discuss ALL
conductivity in that article, not just metals and electrolytes, I should
go add some words about semiconductor's and metal's hole-flow.
a negatively charged particle. This creates an imbalance in the overall
charge of the atom. This phenomenon is not synonymous with a flow of
protons.
Right. Hole current a flow of electrons in the lower "orbit" of the
atoms. But it's also a flow of "vacancies." What I don't know is, what's
the mass of each hole? Does it have the same mass as an electron, or does
it act as if it has negative mass? If holes behave as if they have real
mass, then I would say that they qualify as real positive particles, just
like positrons. If they have anti-mass, then everyone should probably
assume that holes are "really" electrons which move to fill a vacancy, and
hence leave a new vacancy behind them.
It has been my experience that there are still two schools of
thought. Those who believe that current flows from positive to
negative, and those who believe that current flows from negative to
positive. It all depends on your definition of current.
Yes and no. I think that the fight between the two schools of thought is
misguided. If we're talking about "current" as used in physics, then it
is DEFINED as a flow from pos. to neg. No arguments, that's the
definition. By definition we ignore the actual particles and define the
charge carriers as being positive, regardless of whether they are or not.
On the other hand, if we're talking about the actual particles, then the
direction is also not a matter of opinion as long as we have ways to look
at the particles themselves. For example, electrolytes have negative ions
flowing in one direction and positive ions flowing in the other, and so
the "real" direction of current really is in both directions at once.
Build a circuit from hoses full of salt solution if you REALLY want to get
people befuddled! :) In a (non-holes) metal, the moving charges really
are negative, and the direction of charge motion is from negative to
positive.
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William J. Beaty SCIENCE HOBBYIST website
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