Conventional vs Electron theory

Conventional versus
electron flow "The nice thing about
standards is that there are so
many of them to choose from." Andrew S. Tanenbaum,
computer science professor When Benjamin Franklin made
his conjecture regarding the
direction of charge flow (from
the smooth wax to the rough
wool), he set a precedent for
electrical notation that exists to this day, despite the fact
that we know electrons are
the constituent units of charge,
and that they are displaced
from the wool to the wax --
not from the wax to the wool -- when those two substances
are rubbed together. This is
why electrons are said to have
a negative charge: because
Franklin assumed electric
charge moved in the opposite direction that it actually does,
and so objects he called
"negative" (representing a
deficiency of charge) actually
have a surplus of electrons. By the time the true direction
of electron flow was
discovered, the nomenclature
of "positive" and "negative"
had already been so well
established in the scientific community that no effort was
made to change it, although
calling electrons "positive"
would make more sense in
referring to "excess" charge.
You see, the terms "positive" and "negative" are human
inventions, and as such have
no absolute meaning beyond
our own conventions of
language and scientific
description. Franklin could have just as easily referred to
a surplus of charge as "black"
and a deficiency as "white," in
which case scientists would
speak of electrons having a
"white" charge (assuming the same incorrect conjecture of
charge position between wax
and wool). However, because we tend to
associate the word "positive"
with "surplus" and "negative"
with "deficiency," the standard
label for electron charge does
seem backward. Because of this, many engineers decided
to retain the old concept of
electricity with "positive"
referring to a surplus of charge,
and label charge flow (current)
accordingly. This became known as conventional flow
notation: Others chose to designate
charge flow according to the
actual motion of electrons in a
circuit. This form of symbology
became known as electron
flow notation: In conventional flow notation,
we show the motion of charge
according to the (technically
incorrect) labels of + and -. This
way the labels make sense,
but the direction of charge flow is incorrect. In electron
flow notation, we follow the
actual motion of electrons in
the circuit, but the + and -
labels seem backward. Does it
matter, really, how we designate charge flow in a
circuit? Not really, so long as
we're consistent in the use of
our symbols. You may follow
an imagined direction of
current (conventional flow) or the actual (electron flow) with
equal success insofar as circuit
analysis is concerned. Concepts
of voltage, current, resistance,
continuity, and even
mathematical treatments such as Ohm's Law (chapter 2) and
Kirchhoff's Laws (chapter 6)
remain just as valid with
either style of notation. You will find conventional
flow notation followed by
most electrical engineers, and
illustrated in most engineering
textbooks. Electron flow is
most often seen in introductory textbooks (this
one included) and in the
writings of professional
scientists, especially solid-
state physicists who are
concerned with the actual motion of electrons in
substances. These preferences
are cultural, in the sense that
certain groups of people have
found it advantageous to
envision electric current motion in certain ways. Being
that most analyses of electric
circuits do not depend on a
technically accurate depiction
of charge flow, the choice
between conventional flow notation and electron flow
notation is arbitrary . . . almost. Many electrical devices
tolerate real currents of either
direction with no difference in
operation. Incandescent lamps
(the type utilizing a thin metal
filament that glows white-hot with sufficient current), for
example, produce light with
equal efficiency regardless of
current direction. They even
function well on alternating
current (AC), where the direction changes rapidly over
time. Conductors and switches
operate irrespective of current
direction, as well. The technical
term for this irrelevance of
charge flow is nonpolarization. We could say then, that
incandescent lamps, switches,
and wires are nonpolarized
components. Conversely, any
device that functions
differently on currents of different direction would be
called a polarized device. There are many such polarized
devices used in electric circuits.
Most of them are made of so-
called semiconductor
substances, and as such aren't
examined in detail until the third volume of this book
series. Like switches, lamps,
and batteries, each of these
devices is represented in a
schematic diagram by a unique
symbol. As one might guess, polarized device symbols
typically contain an arrow
within them, somewhere, to
designate a preferred or
exclusive direction of current.
This is where the competing notations of conventional and
electron flow really matter.
Because engineers from long
ago have settled on
conventional flow as their
"culture's" standard notation, and because engineers are the
same people who invent
electrical devices and the
symbols representing them,
the arrows used in these
devices' symbols all point in the direction of conventional
flow, not electron flow. That is
to say, all of these devices'
symbols have arrow marks
that point against the actual
flow of electrons through them. Perhaps the best example of a
polarized device is the diode. A
diode is a one-way "valve" for
electric current, analogous to a
check valve for those familiar
with plumbing and hydraulic systems. Ideally, a diode
provides unimpeded flow for
current in one direction (little
or no resistance), but prevents
flow in the other direction
(infinite resistance). Its schematic symbol looks like
this: Placed within a battery/lamp
circuit, its operation is as such: When the diode is facing in the
proper direction to permit
current, the lamp glows.
Otherwise, the diode blocks all
electron flow just like a break
in the circuit, and the lamp will not glow. If we label the circuit current
using conventional flow
notation, the arrow symbol of
the diode makes perfect sense:
the triangular arrowhead
points in the direction of charge flow, from positive to
negative: On the other hand, if we use
electron flow notation to show
the true direction of electron
travel around the circuit, the
diode's arrow symbology
seems backward: For this reason alone, many
people choose to make
conventional flow their
notation of choice when
drawing the direction of
charge motion in a circuit. If for no other reason, the
symbols associated with
semiconductor components
like diodes make more sense
this way. However, others
choose to show the true direction of electron travel so
as to avoid having to tell
themselves, "just remember
the electrons are actually
moving the other way"
whenever the true direction of electron motion becomes an
issue. In this series of textbooks, I
have committed to using
electron flow notation.
Ironically, this was not my first
choice. I found it much easier
when I was first learning electronics to use conventional
flow notation, primarily
because of the directions of
semiconductor device symbol
arrows. Later, when I began
my first formal training in electronics, my instructor
insisted on using electron flow
notation in his lectures. In fact,
he asked that we take our
textbooks (which were
illustrated using conventional flow notation) and use our
pens to change the directions
of all the current arrows so as
to point the "correct" way! His
preference was not arbitrary,
though. In his 20-year career as a U.S. Navy electronics
technician, he worked on a lot
of vacuum-tube equipment.
Before the advent of
semiconductor components
like transistors, devices known as vacuum tubes or electron
tubes were used to amplify
small electrical signals. These
devices work on the
phenomenon of electrons
hurtling through a vacuum, their rate of flow controlled by
voltages applied between
metal plates and grids placed
within their path, and are best
understood when visualized
using electron flow notation. When I graduated from that
training program, I went back
to my old habit of conventional
flow notation, primarily for the
sake of minimizing confusion
with component symbols, since vacuum tubes are all but
obsolete except in special
applications. Collecting notes
for the writing of this book, I
had full intention of illustrating
it using conventional flow. Years later, when I became a
teacher of electronics, the
curriculum for the program I
was going to teach had
already been established
around the notation of electron flow. Oddly enough, this was
due in part to the legacy of my
first electronics instructor (the
20-year Navy veteran), but
that's another story entirely!
Not wanting to confuse students by teaching
"differently" from the other
instructors, I had to overcome
my habit and get used to
visualizing electron flow
instead of conventional. Because I wanted my book to
be a useful resource for my
students, I begrudgingly
changed plans and illustrated it
with all the arrows pointing
the "correct" way. Oh well, sometimes you just can't win! On a positive note (no pun
intended), I have subsequently
discovered that some students
prefer electron flow notation
when first learning about the
behavior of semiconductive substances. Also, the habit of
visualizing electrons flowing
against the arrows of
polarized device symbols isn't
that difficult to learn, and in
the end I've found that I can follow the operation of a
circuit equally well using
either mode of notation. Still, I
sometimes wonder if it would
all be much easier if we went
back to the source of the confusion -- Ben Franklin's
errant conjecture -- and fixed
the problem there, calling
electrons "positive" and
protons "negative."