WHEN STATIC ELECTRICITY FLOWS...
© 1997 William J. Beaty
Someone on phys-L discussion recently mentioned "Electricity at rest".
Uh oh. Stamping out "Static" electricity is yet another one of my
crusades! Below is Yet Another Electricity Rant.
;)
I object to the "Static Electricity" and "Electricity at Rest" concepts
because they are immensely confusing to naive learners. The terms
mistakenly imply that "static" must *exclude* electric current, and vice
versa. They wrongly imply that "static" and "current" can never occur
simultaneously, and they incorrectly suggest that "static" is the opposite
of "current".
In reality, electrostatic and electric current phenomena can occur in the
same wire at the same time, and it's perfectly possible to have a FLOW OF
STATIC ELECTRICITY. But because the terminology so strongly implies
otherwise, "flowing static" seems impossible, if not outright
blasphemous. The trouble is simple. Electrostatics does not involve
"electricity at rest" at all. Instead it involves charge imbalances and
electric fields. Whether the charges move or not is irrelevant, and
sometimes the charges do move. Yet when the charges begin moving, none of
the electrostatic phenomena vanish.
What do I have against "Electricity at Rest?" Here's an example. Take a
pair of parallel wires, connect a power supply to one end, and a load
resistor to the other end. An electric current appears, the load resistor
grows warm, and most students would swear that no "Static Electricity"
exists in this example. However, the two wires have opposite surface
charges, and the electrostatic field between them is the same e-field
which drives the charge drift within the resistor. Without surface
charges and e-fields, there can be no current in the resistor or in the
wires. The battery/resistor example is inherently an electrostatic
system. Yet since it is not "Electricity at Rest", it cannot involve
"Static Electricity." Right? Batteries and resistors deal with Current,
so there can be no Static, right? Wrong. Without electrostatics, there
can be no electric current in a circuit. Current in wires is caused by
electrostatic forces.
Here's a slightly altered example. Connect a 100,000v DC power supply to
a pair of bare parallel wires, and connect the other end to a long neon
sign tube. The tube lights up, and a few tens of milliamps flow in the
connecting wires. At the same time the wires will attract lint, cause
arm-hair to rise, crackle gently if touched by an UNgrounded person, and
cause electroscope foil leaves to open. "Electricity at Rest" is clearly
present. However, those same surface charges which cause the obvious
electrostatic phenomena are moving. They are participating in the
electric current, therefor there is no "Electricity at Rest" anywhere to
be found! So, how can hair be rising? The charges are flowing, they are
not "static." Why are they behaving as if they were "Electricity at
Rest", when they are actually an electric current?
Another example: consider a metal ring. The ring contains a vast
quantity of electrons in its electron sea. There is no net current,
therefor the metal is full of "Electricity at Rest." So, where are all
the electrostatic phenomena, the "static electricity?" Yes, yes, I
realize that the electrons and protons cancel each other. But from a
naive student standpoint, the metal is full of charge, the charge is not
moving, and that is the very definition of "Static Electricity." So where
is it? And if I move a permanent magnet near the ring, a current appears
and then vanishes, and the charges in the metal go from "static" to
"flowing" and back to "static." Yet electrostatic phenomena do not appear
and vanish. From a naive student standpoint, something is seriously wrong.
Charges are unmoving, but no "static electricity" appears.
Another: when mentioning these ideas to people, some will defend to the
death that the surface charges in an electric circuit are locked in place,
that they are "static", and do not participate in any electric currents in
the metal. I have no answer to this. As far as I know, it is a brand new
physical phenomenon. The surface charges experience infinite resistance
and do not flow? Even though they are part of a metal and exposed to an
e-field? I thought the surface charge was a net charge; the difference
between electron and proton densities, and did not even involve individual
particles. I suspect that this is true, and suspect that the "static
electricity" concept is so virulent that it forces people to insist on
strange phenomena whose only function is to force the charges to obey the
"rules" and remain static. And besides, if you charge up a bowl of small
metal parts, then pour the charged parts out in a stream, you definitely
have e-fields and surface charge, and you definitely have an electric
current as well. You have a FLOW of "static electricity." You have
electric *current* that is composed of "Electricity at Rest." The same is
true of electron beams in vacuum, charged paint from electrostatic
sprayers, charged rain in thunderstorms, belts on VandeGraafs, etc., etc.
The so-called "Electricity at Rest" is *flowing* along and causing a
current, all the while maintaining every bit of its "static electric"
nature.
One last example: suppose you hook a battery to a light bulb. Electric
current appears in the connecting wires. Now break the circuit. The
flowing charges do not zoom back into the battery, instead they halt where
they are. In other words, they change from "current electricity" to
"static electricity." Hmmm. Is something wrong here? An inactive
flashlight circuit obviously does not attract lint nor deflect
electroscopes, but when you suddenly turn off the switch, you by
definition create "static electricity". So why don't the wires suddenly
become "static-y"? Why don't electrostatic phenomena suddenly appear when
the moving charges becomes "static?" Because "static electricity" is
imbalanced charge, not unmoving charge. It involves high voltages, not
lack-of-current.
In all of the above examples, everything becomes clearer if we strike out
the words "static electricity" and replace them with "imbalanced charges."
There is no be problem in accepting that an imbalance of something might
be able to move along. If the attracted lint and crackling sparks are
caused by imbalanced charge, then we won't become confused when charges
start flowing and stop. "Charge imbalance" and "charge flow" won't be
seen as mutually exclusive phenomena, and all the screwy mistakes go away.
Maybe my ideas can be clarified by an analogy with Newtonian Mechanics.
Mechanics is divided into Statics and Dynamics. In Statics we study mass
and forces. In Dynamics we study motion, acceleration, and changing
forces. However, it would be obviously ridiculous to assert that
"dynamics" phenomena exclude any "statics" concepts such as mass and
force. It would be wrong to say that mass and forces must disappear
whenever a situation fell under the realm of Newtonian Dynamics. It would
be even sillier to assert that there is a phenomenon called "Static
Mechanicity", which appears whenever "Mechanicity" is at rest, and
vanishes whenever the "Mechanicity" flows or becomes Dynamic. Yet this is
just what we constantly say in introductory Electrical science. We state
that when electric current commences, "Static Electricity" must
disappear, because "static" and "dynamic" are incompatible, and clearly
the "static" has disappeared when motion commences. This is screwy.
Newtonian "statics" and "dynamics" are two ways of looking at the world,
not two types of energy or substance. The same idea applies to "static"
and "current." They are fields of science, not substance or energy.
An overly-quick solution: in textbooks and education articles, banish the
phrase "electricity at rest." Instead, state
that Newtonian Statics deals with forces, not with "matter at rest." And
so Electrostatics becomes a phenomena involving charge imbalance and
e-fields, not "electricity at rest". When masses begin accelerating, it
does not mean that "Static Mechanicity" is gone, that all forces vanish,
or that Newtonian Statics has suddenly become meaningless. So when
currents appear in a circuit, it doesn't mean that all the electrostatic
phenomena in the circuit become smaller by any amount.
But this solution does not help those who *already* have fallen prey to
the "unmoving electricity" concept. If we suddenly stop teaching a
misconception, we don't magically remove it from students' minds, from K-6
textbooks, or from popular culture. Silently fixing our own behavior
mainly protects us from criticism, it does not solve the problem.
A better solution: engage in warfare; intentionally teach all of the above
material. Admit that we've screwed up in the past, then publicly set
things right. Point out the problems to our students in no uncertain
terms. Attack the misconceptions directly. Expose the rot to daylight
and fresh air.
.