WHICH WAY DOES THE
"ELECTRICITY" REALLY FLOW?
(C)1996 William Beaty
Electronics teachers and authors of textbooks are often chided for
passing on an "error" to their students. Teachers promote the (wrong?)
idea that electric current is a flow of positive particles in one
direction, when supposedly it's really a flow of negative electrons going
the other way.
In fact, the chiders are wrong. They labor under the misconception
that "Electricity" is made of negatively-charged particles called
electrons. This fundamental error
leads most people to imagine that electric currents are always a
flow of negative particles. Actually, in some conductors the electric
currents are a flow of genuinely positive charges, while in others the
flows are indeed negative particles. And sometimes the currents are both
positive and negative particles flowing at once, but in opposite
directions within the same conductor. We cannot arbitrarily decide which
way the charges flow, since their true direction always depends on the
type of conductive material.
Electricity is more than just electrons
"Electricity" is not made of electrons (or to be more specific, Electric Charge, which is sometimes called "Quantity of Electricity," is not made of electrons.) Charge actually comes in two varieties: positive particles and negative. In the everyday world of electronics, these particles are the electrons and protons supplied by atoms in conductors. Physicists may additionally deal with other charged particles: muons, positrons, antiprotons, etc. But the "electricity" in common electrical devices is limited to positive protons and negative electrons.
Because the negative particles carry a name that sounds like
"electricity," people unfortunately start thinking that the electrons ARE
the electricity, and they think that that protons (having a much less
electrical name?) are not electrical. Some text and reference books even
state this outright, saying that electricity is composed of electrons.
Nope. In reality the electrons and protons carry electric charges of
equal strength. If electrons are "electricity", then protons are
"electricity" too.
Now everyone will rightly tell me that the protons within wires cannot
flow, while the electrons can. Yes, this is true... but only true for
metals. And it's only true for solid metals. All metals are composed of
positively charged atoms immersed in a sea of movable electrons. When an
electric current is created within a solid copper wire, the "electron sea"
moves forward, but the protons within the positive atoms of copper do not.
However, solid metals are not the only conductors, and in many
other substances the positive atoms *do* move, and they *do* participate
in the electric current. These various conductors are nothing exotic.
They are very common, they all around us; as close to us as they can
possibly be.
Non-electron Charge-flow
For example, if you were to poke your fingers into the back of an old-style television set, you would suffer a dangerous or lethal electric shock. During your painful experience there obviously was a considerable current directed through your body. However, no electrons flowed through your body at all. The electric charges in a human body are entirely composed of positive and negative charged atoms or "ions." During your electrocution, it was these charged atoms which flowed along as an electric current. The electric current was a flow of positive sodium and potassium atoms, negative chlorine, and numerous other more complex
So, inside human flesh, which direction did the electric
current REALLY go? Do we follow the negative particles and ignore the
positive ones? Or vice versa, following the positives? There is a simple
answer, but first...
Batteries are another example of non-electron or "ionic" conductors.
When you connect a lightbulb to a battery, you form a complete circuit,
and the path of the flowing charge is through the inside of the
battery, as well as through the light bulb filament. Battery electrolyte
is very conductive. Down inside the battery, within the wet chemicals
between the plates, the amperes of flashlight current appears as a flow of
both
positive and negative atoms. There is a powerful flow of electric charge
going through the battery, yet no individual electrons flow through the
battery at all. So, while the current is between the two plates of the
battery, what's its real direction? Not right to left, not
left to right, but in both directions at once. About half of the
charge-flow is composed of positive atoms, and the remaining portion is
composed of negative atoms flowing backwards. Of course in metal
wires outside the battery, the real particle flow is only from negative to
positive. But
inside the battery's wet electrolyte, the charge-flow goes in two opposite
directions at the same time. (And if we built a circuit from hoses
full of salt water, with no metal conductors used, then all the
current would be bi-directional.)
Two-way currents are common
There are many other places where this kind of positive/negative charge flow can be found. In the following list of devices and materials, electric charges found within conductors are a combination of movable positive and negative particles. During an electric current, both varieties of particles are flowing past each other in opposite directions.TWO-WAY POS/NEG ELECTRIC CURRENTS CAN EXIST IN:
- batteries
- human bodies
- all living organisms
- the ground
- the ocean
- the sky (ionosphere)
- electrolytic capacitors
- aluminum smelters
- liquid mercury and solder
- ion-based smoke detectors
- electroplating tanks
- electrophoresis gels in research (esp. DNA testing)
- air cleaners, smoke precipitators
- particle beams
- the vertical "sky current" in the atmosphere
- gas discharge, which includes:
- electric sparks
- fluorescent tubes
- sodium and mercury arc streetlights
- neon signs
- the Earth's Aurora
- lightning and corona discharges
- arc welders
- Geiger counter tubes
- thyratron tubes
- mercury vapor rectifiers
This list is not so short. Again I ask you, what is the REAL direction of
electric
current? We cannot solve the problem by belittling it, or by pretending
that two-way currents pertain only to something exotic, or pretend that
it's separate from everyday life. Our own nervous system is based on
two-way currents. We dare not think that a current
in a wire is "real," while currents in human flesh are not.
Well, what is "current?"
To gain some insight, let's examine the details. When trying to understand electric circuits and electrical measurements, we need a simple way to take measurements of the important entity named Electric Current. But to measure currents, won't we first need to measure how much of the current is composed negative particles going one way, and positive particles the other? Yes, but we ONLY need this if we want to know EVERYTHING about the electric current. The flowing negatives and positives are usually not equal, and the speed of the positives in one direction is usually not the same as the speed of the negatives in the other. Electric current can be complicated! However, there is a cute trick we can pull in order to avoid having to look at the particles at all. And that trick holds the answer to the question.
Electric currents produce three main effects: magnetism, heating, and
the voltage drop across resistive conductors. These three effects cover
almost everything we encounter in electronics. And these three effects
don't care
about the amounts of positive and negative particles, or about their
speed, their mass, their charge, etc. If a hundred positive particles
flow to
the left
per second, this gives EXACTLY as much magnetism, heating, and voltage
as a hundred NEGATIVE particles flowing to the right per second.
(Note: this is because reversing the polarity of the particles reverses
the current, and reversing the particle direction reverses the
current again! Two negatives make a positive.) Magnetism, heating, and
voltage drop together represent
nearly every feature that's important in everyday electrical circuitry.
Therefore, as far as most electrical devices and circuits are concerned,
it
makes
no difference if the current is made of positive particles going one way,
or negative particles going the other... or half as many negatives flowing
backwards through a crowd of half as many positives.
Put simply, the "Ampere" doesn't care about the direction or
speed of
the flowing particles.
So, in order to simplify our measurements and our mental picture
of
Electric Currents, we cut away the unused parts of the picture. We make
the negative particles positive, then add their current to any positive
particles which were flowing forward. We stop thinking of current as
being a
flow of charges. Instead we intentionally define "electric
current" as being a flow of exclusively positive particles flowing in one
particular direction. We don't care about the real polarity of the
particles. We don't care about their speed, and we don't care about their
number. We ignore both the chemical effects and the effects of the
velocity and direction moving particles. We ignore the collisions between
positive and negative particles. All we care about is the total net
charge
which moves past a particular point in the circuit. The real charges are
too complicated to deal with, and the added complexity gets us very little
information as long as we're only interested in voltage drop, magnetic
fields, and heating.
Particle-flow is real, "Amperes" are not
Once we start ignoring the speed and direction of the charges, then we can easily build electrical instruments or "amp meters" which measure the Conventional Electric Current in terms of the magnetism which the charge-flow creates... or by the voltage drop which appears across a resistor, or by the temperature rise being created in a calibrated piece of resistance wire. These three types of meter will agree that a "current" is a "current" regardless of the particle polarities and flows. Then we can use these meters everywhere. In nearly every situation they will tell us all we could ever want to know about flows of charged particles in any circuit. An amp-meter might not be appropriate when used in an exotic physics experiment. It won't paint the correct picture when designing electron beams inside vacuum tubes. It cannot detect real current, instead it only measures our conventionally-defined simple current. But for more than 99% of electricity and electronics, the direction of the particles is irrelevant, and an ammeter tells us the so-called "real" current while hiding the true particle flows.
Or to put it simply: we pretend that "electric currents" are always
composed of POSITIVE particles, so that any negative currents are defined
as positive particles flowing backwards rather than negative particles
flowing forwards.
Confusing students for two hundred years
We do cause some problems by choosing a positive charge convention. For example, what happens if we all spend many years thinking in terms of such simplified "electric current?" Might we eventually start believing that this oversimplified concept of positive electric current is REAL? Yet it's not real, it's simply one way to simplify things. There's a genuine difference between the simplified picture versus the actual particle flows. The Amps would not quite match a visual picture of moving particles. But if we truely believe that the amperes are real, we might start to doubt the existence of flowing charges. We might start to see "Electric Current" itself as a sort of abstract, invisible, difficult-to-image thing. We might lose track of the facts that electric current is an actual flow of matter. We might lose track that there are real, visible particles flowing along inside that circuit, or that these particles have an actual average speed, mass, and direction.
Because "amperes" are so incredibly useful, the simplified interpretation
of Current takes over and becomes more real than reality. It
allows us to understand parts of physical science which otherwise might be
too complicated to imagine. But in letting the positive charges take
over, some nagging questions are left behind, such as "WHICH WAY DOES THE
ELECTRICITY REALLY FLOW?" (grin!)
PS
This over-simplified fake electric current measured by ammeters is commonly called "Conventional Current." The link gives 16,000 google hits. By convention, we define the flowing charges to be positive. Yet something is missing! Nobody talks about the "Conventional Charge!" No google hits! The conventional current must be a flow of conventional charge, so first we should teach our students about the existence of oversimplified charges, "conventional charges," charges which we pretend are inside all the wires. If we did this, then "conventional current" would be much easier to accept, no?
