THIS IS PAGE 2 OF 'ELECTRICITY MISCONCEPTIONS'
Many authors bemoan the fact that Ben Franklin labled "resinous electricity"
as negative, and "vitreous electricity" as positive. By choosing the polarities
this way, Franklin forces us to say that electric current is a flow of NEGATIVE
charge rather than positive charge.
Did Franklin make a mistake? ABSOLUTELY NOT. In fact it's a blessing, because
flows of negative charge aren't inherently confusing. Common and widespread
misconceptions make them confusing. If Franklin had instead chosen
electrons to be positive, then we could easily ignore those misconceptions. We'd
end up with the illusion of understanding, yet we'd have all sorts of niggling
unanswered questions caused by the misconceptions. The solution is not to cover
up the misconceptions and pretend that we understand electricity. The solution
is to confront our misconceptions. If we dislike negative currents or
find them to be confusing, it's because our misconceptions are fighting back.
What misconceptions? There are several:
Here are the corrections for the above seven mistakes:
To clarify this, get rid of the battery. Instead, use a hand-cranked
generator as your power supply. Ask yourself exactly where the "electricity"
comes from when a generator powers a light bulb. A generator takes electrons in
from one terminal and simultaneously spits them out the other one. At the same
time, the generator pushes electrons through the moving coil of wire inside
itself and through the rest of the circuit. Unlike a battery-powered circuit,
all we have is wires. Where is the source of "electricity?" When we include the
generator in the circuit, we find that the circuit is a continuous closed loop
of wire, and we can find no original source of the "electricity." A generator or
battery is like a closed-loop pump, but it does not supply the substance being
pumped. But we were all taught that "batteries and generators create current
electricity." This phrase forms a serious conceptual stumbling block (at least
it did for me!) To fix it, change the statement to read like this instead:
"batteries and generators cause electric charge to flow." To complete the
picture, add this: all conductors are full of movable charge.
A battery or generator is like your heart: it moves blood, but it does not create blood. When a generator stops, or when the metal circuit is opened, all the electrons stop where they are, and the wires remain filled with electric charges. But this isn't unexpected, because the wires were full of vast quantities of charge in the first place.
Much of this problem would vanish if we used the word "electricity" only to
refer to a field of science or class of phenomena. This is the way we use the
words "physics" or "optics." Then, if we needed to get down to details, we would
never say "electricity." Instead we would use words like "charges," "energy",
"current," etc. We do use the word "electricity" this way occasionally. But then
we immediately turn around and do the equivalent of teaching our children that
optics is a substance, or that physics is a kind of energy. "Optics" is a
substance which comes out of the light bulb and passes through the lens, right?
And when you ride a bicycle, "physics" comes out of your muscles and makes the
wheels turn? That's what we say when we tell kids that "electricity flows in
wires".
Below are a few examples of errors caused by the contradictory meanings.
Which is right? All and none, because the word "electricity" has multiple contradictory definitions. None of the above statements are right because there is no "electricity" which is charge, energy, power, and phenomena all at once. And all the meanings are also correct, because the word "electricity" is commonly used to name all these different things, and these definitions appear in the dictionary. Who are we to argue with The Dictionary? Yet we SHOULD distrust the dictionary, since it just innocently records the words which people use. If people always use the word "electricity" in misleading and contradictory ways, then dictionaries will contain contradictory definitions.
Somewhere along the line the school textbooks made the problem worse by creating a third meaning. They started teaching that "electricity" was the motion of the charges inside the wires; it was the current. So while scientists were saying that electrons are particles of electricity, school textbooks were saying that the MOTION of the electrons was really the electricity. Both can't be right! And to make matters worse, "Electricity" became the name for electrical phenomena. In other words, charges and currents in nerve cells are "bioelectricity", while charges and currents in the earth are "geoelectricity," and charges and currents in combed hair are "triboelectricity." Knocking rocks together creates piezoelectricity, and contracting muscles use myoelectricity. Does this mean that there are many different kinds of electrons? Or many kinds of electrical energy? Of course not. Bio, geo, tribo-electricity are subject headings in science books. They are different kinds of electrical science, not different kinds of "electricity." Today when unwary teachers try to understand "electricity", they encounter this morass of contradictions. Often they throw up their hands in frustration and say: "Electricity is just a kind of event." This is wrong. The truth is that the word "Electricity" has many contradictory meanings and so has become meaningless. Electricity is not an event. Neither is it energy, or electrons, or electron motion. Electricity is just a big mistake, but a mistake that crept up slowly on everyone, so we never realized it was happening. As long as we keep trying to define "electricity", we will keep spreading confusion. The only honest move is to stop covering up the problem and admit that we've been accidentally misleading generation after generation of students by teaching them about the wonderful substance called "electricity."
Not all of the electrons become "loose" and begin wandering. Many are held
back, and they remain attached to the atoms. Only the outer electron(s) become
part of the "electron sea." Different metals donate different numbers of
electrons to the sea: in some metals, each atom only loses one electron, while
in other metals two or more become free. The metal is composed of a mixture: a
solid grid of positively-charged atoms which are immersed in a see of movable
electrons. When there is an electric current in a wire, it is these movable
electrons which flow. These electrons are not stuck to individual metal atoms,
so the electrons do not need to "jump" during an electric current.
The orbiting motion of the metal's "liquid" electrons takes place at high speed. However, this motion is similar to the random thermal vibrations of a gas. For this reason we normally ignore the electrons' wandering motion, just as we ignore the vibration of air molecules when we talk about "wind." Air molecules keep moving fast even when there is no wind at all. And electrons in metals always wander around at high velocity, even when the electric current is zero.
To aid your understanding, imagine a large wheel. If you give it a spin, the
entire wheel moves as a unit, and this is how you transmit mechanical energy
almost instantly to all parts of the wheel's rim. But the wheel itself didn't
move very fast. The material of the wheel is like the electrons in a wire.
Electrical energy is like the "jerk," the mechanical energy wave which you sent
to all parts of the wheel when you gave it a spin. Mechanical energy moves
incredibly quickly to all parts of the wheel, but the wheel's atoms didn't have
to rapidly travel anywhere in order for this to happen. MORE
If you insist that "Static" and "Current" are two kinds of electricity, then
please explain this: if positive and negative charges are forced to separate as
they flow along a wire, then that wire becomes electrostatically charged... yet
the charges are NOT STATIC. The wire will cause hair to rise, and it can attract
fur or lint, yet the so-called "static electricity" is moving along as an
electric current. Does this make your brain ache? The solution is simple:
realize that "static" electricity is actually composed of separated opposite
charges, and if those separated charges should flow along, they still behave as
"static electricity" whether they move or not. The separation of the charges is
key, and their "static-ness" is not important. For this reason, charges can
exhibit both "static electricity" and "current electricity" at the same time.
This is not so terrible, since water supplies a good illustration: water can be
pressurized and it can flow at the same time. Fortunately we have not given the
name "static water" to water that is pressurized. Maybe we should change the
name of "Static electricity" to something sensible, like "charge imbalance", or
"pressurized electricity." It would end a lot of confusion.
Charges can flow, and opposite charges can be forced to separate, but this
doesn't mean that the two KINDS of charge are "flowing electricity" and
"separated electricity." Separation and flow are two electrical behaviors, they
are not two "kinds of electricity."
More about this: WHAT IS
ELECTRICITY?
"Static" is a separation; it is a stretching-apart, and it really has little to do with anything remaining static or stationary."Static electricity" was misnamed, and it really should be called "charge separation" or maybe "stretched electricity." Since stretch is not the opposite of flow, Static is not the opposite of Current. And though electric current really exists and electric charge really exists, there is no such material as either "current electricity" or "static electricity." See MORE on this topic.
"Current" is a flowing motion. It has little to do with the separation of opposite charges.
Another question: what if the English language had no word for "water", but
instead we called it "current"? What if we really believed that rivers were full
of "current" which flowed? Wouldn't people tend to acquire many serious
misconceptions about the nature of water? We might imagine that it vanishes
whenever it stops flowing, since a halted current is... nothing! A glass of
water would seem very confusing, since the glass would be full of stationary
"current."
As far as elementary textbooks are concerned, we have no name for the stuff
that flows inside of wires. The stuff, when it flows, is properly called "an
electrical current", but when the stuff *stops* flowing, what do we call it?
Refer to advanced physics texts, and there we'll find its correct name: Charge.
An electric current is a FLOW OF CHARGE. Yet the K-6 books never mention this.
Instead they say that "current" flows. They say it over and over and over, and
any students are very lucky if they avoid picking up the wrong idea that the
charges vanish when the flow is halted. (Does the water in a pipe suddenly
evaporate when you halt its flow?.)
Worse, most books say that "current electricity" flows in wires. To this I
say, "Is there a special kind of water called 'current water?'" The answer
obviously is NO. The same answer applies to electricity: electricity can flow
and electricity can stop, and a flow of electricity (or charge) is called an
Electric Current, but there is no such thing as "current electricity."
Here's a useful hint for authors: in your articles, temporarily remove the
word "current" and replace it with "charge flow", then see if your sentence
still makes sense. If the sentence states that charge-flow is flowing, then that
particular sentence is confusing the students and teaching them to believe that
a substance called "current" exists.
In an electric circuit, the path of the electric charges is circular, while
the path of the energy is not. A battery can send electric energy to a light
bulb, and the bulb changes electrical energy into light. The energy does NOT
flow back to the battery again. At the same time, the electric current is a
circular flow, and the charges flow through the light bulb filament and all of
them return to the battery.
Electric energy can even flow in a direction OPPOSITE to that of the electric
current. In a single wire, electric energy can even move continuously forward
while the direction of the electric current is alternating back and forth at
high frequency.
Here's one way to clarify the muddled concepts: if electric current is like
wind, then electrical energy is like some sound waves, and electrons are like
the molecules of the air. For example, sound can travel through a pipe if the
pipe is full of air molecules, and electrical energy can flow along a wire
because the wire is full of movable charges. Sound moves much faster than wind,
correct? And electrical energy moves much faster than electric current for much
the same reason. Air in a pipe can flow fast or slow, while sound waves always
move at the same very high speed. Charges in a wire can flow fast or slow, while
electrical energy always flows along the wire at the same incredibly high speed.
Whenever sound is flowing through a pipe, the air molecules in that pipe are
vibrating back and forth. When waves of AC electrical energy are flowing along a
wire, the electrons in that wire are vibrating back and forth 60 times per
second.
Suppose that we were all taught that sound and wind are the same thing? This
would prevent us from understanding wind or sound. K-6 textbooks teach us this.
They say that electric currents are a flow of energy, as if wind was really
sound. It completely prevents us from understanding both electric current and
energy flow. Be careful, since my description of the above pipes are just an
analogy, and sound waves aren't *exactly* like electrical energy. For example,
sound can flow inside an air-filled tube, while electrical energy always flows
in the space outside of the wires, and does not travel along within the metal
wires. However, electrical energy is coupled with compression waves in the
electrons of the wire. Electron-waves travel inside the wires, yet the energy
they carry is in the invisible fields surrounding the wires.
Is it important for us to realize that wind is not sound? Obviously. School books would cause harm if they taught us that wind is sound. And if we want to understand circuits, we need a clear view of electric charge flow, and of electric energy flow. We need to be totally certain that they are two different things, and our textbooks teach us the exact opposite!
In any simple electric circuit, the path of the electric current is a
complete circle. It is like a drive belit, and it has no starting point. It goes
through all parts of the circuit including the battery, and including the
battery's liquid electrolyte. If there's one Ampere in the wires connected to
the battery, then there's also a 1-Amp flow of charge in the electrolyte between
the battery's plates. Where does this charge come from? Go down to this section.
A battery does not supply charges, it merely pumps them. Whenever electric
charge flows into one terminal of a battery, an equal amount of charge must flow
THROUGH the battery and back out through the other terminal. In a simple
battery/bulb circuit, the charges flow around and around the circuit, going
through both the battery and the bulb. The battery is a charge pump.
Here's an analogy which may help explain it: imagine a wheel that's free to
spin. For example, turn a bicycle upside-down in your mind. Give the front tire
a spin. When you spin the tire, your hand injects energy into the whole wheel
all at once. Now put your hand lightly against some part of the tire so the
spinning wheel is slowed and stopped by friction. Your hand gets hot. Your hand
extracts energy from the entire wheel, all at once, and the whole wheel slows
down. Finally perform both tasks at once: rub one hand lightly against the tire
while you use your other hand to keep the wheel spinning. Would it be right to
tell students that the "Power" hand fills each rubber molecule with energy, that
the molecules travel to the "Friction" hand and dump their energy, then they
return empty to the "power" hand and get refilled? No, of course not! If this
were true then your "friction" hand wouldn't experience any friction until those
magic energized rubber molecules made their way around the rim. Part of the
wheel would be spinning while part would be de-energized and unmoving, and this
would be really a strange sight to see!
A flashlight circuit is like our bicycle wheel. The electrons in the copper
circuit are like the rim of the wheel. They are like a drive belt inside the
wires. The battery causes ALL the electrons in the loop of wire to begin moving,
and so it injects energy into the WHOLE CIRCUIT all at once. As soon as the
battery moves the electrons, the distant lightbulb lights up. The electrons
moving into the bulb's filament are exactly the same as the ones moving out; the
bulb doesn't change them or extract stored energy from them. Did your hand alter
the rubber tire as it rubbed on the bicycle wheel? No, it just slowed the whole
wheel down. It extracted energy from the whole wheel, and was heated by
friction. Same thing with the bulb, it slows ALL the electrons down throughout
the entire circuit, and in this way extracts energy from the whole circuit as it
lights up.
In discussing this misconception with teachers, I find that they see nothing
wrong with it. The kids instantly grasp the "freight cars" story since it is
very visible, and it offers a sensible explanation. What more can we ask? Yet
there is a serious problem: in order to really understand electricity in later
years, a student must UNLEARN the misleading freight-cars analogy. "Unlearning"
rarely happens, and so the analogy forms a learning barrier which can forever
prevent any further progress. It freezes their understanding of electricity at
the elementary-school stage. Yes, if the kids will never have any need to
understand how electricity REALLY works, then the freight-cars analogy is fine.
But if the kids grow up to become scientists and engineers and technical people,
then the freight-cars analogy causes harm. (Unfortunately, it causes FUTURE
harm, so K-6 educators never see the effects of the misconception that they've
installed in the kids minds.)
The "filled freightcars" analogy seems seductively appropriate when used to
explain Direct Current. However, when explaining Alternating Current the analogy
breaks down completely. Each freight car wiggles back and forth, so how can
those energy-filled buckets move from the "battery" to the "light bulb?" They
cannot. The analogy doesn't work, and students who have learned the analogy will
find it impossible to understand AC. Again, this is fine if the kids have no
hopes of entering any kind of technical career; if their science learning will
cease after fifth grade...
An analogy regarding this analogy (grin!) How do sound waves work? Would it
be OK to teach kids that your vocal chords place energy into air molecules, then
the air molecules zoom out of your mouth at 720MPH and crash into the ears of
distant listeners? I would think that any author who use this kind of
explanation should be ashamed. Yes, the explanation "works", and it is easy for
the kids to grasp. But it is wrong. And any kid who believes this explanation
will have terrible difficulties should they ever have need to understand how
sound REALLY works. This is an analogy for wires, since electrical energy is
wave energy, and the electrons in the wires do not move along with the
speed-of-light energy waves.
The bicycle-wheel analogy has no problem explaining AC. Just wiggle the bicycle wheel back and forth instead of spinning it continuously. The wiggling wheel will rub upon the distant "friction" hand, and heat it up. Energy can travel instantly across the bicycle wheel, even though the wheel itself rotates slowly. Energy can travel instantly between the hands even if the wheel moves back and forth instead of spinning.
For example, even when metals are totally neutral, they contain vast
quantities of movable electrons. So, should we say that they contain zero charge
because they are neutral? Or, should we say that they contain a very large
amount of electric charge, because they are filled with electrons? Don't answer
yet, because your answer might be inconsistent with how we describe capacitors
(further below.)
Another: if I place an electron and a proton together, do I have twice as
much charge as before, or do I have a neutral hydrogen atom with no charge at
all? What I DO have is confusion. Misuse of "charge" makes descriptions of
electric circuits seem complex and abstract, when the explanations are really
just wrong.
Another: electric currents in wires are actually a motion of "neutralized"
charge, where every electron has a proton nearby. If we teach that a wire is
uncharged, and we ALSO teach that electric current is a flow of charge, how can
anyone make sense of a situation where a wire has no charge at all, yet contains
an enormous flow of charge? We could say "Oh, but most electric currents are
usually a flow of Uncharged Charge." WHAT? What would a student make of THAT
statement? Can you see the problems that arise because of the word "charge?"
Another one: as you "charge" a battery, you cause an electric current to
appear in the electrolyte, and this motion of electric charges causes chemical
reactions to occur upon the surfaces of the battery's plates. Chemical "fuel"
accumulates, but charge does not: the charges flow into (or out of) the surfaces
of the plates and do not accumulate there. A "charge" of chemical energy is
stored in the battery, but electrical charge is not. And when a battery is being
"discharged", it's chemical fuel drives a process which pumps charge through the
battery. The fuel will eventually be exhausted, but the total electric charge
within the battery will never change!
Here's a way to imagine the process: a battery is like a spring-driven "wind
up" water pump. Send water backwards through this pump, and you wind up the
spring. Then, provide a pathway between the inlet and the outlet of the pump,
and the spring-motor will pump the water in a circle. But now think for a
moment: the water is the charge, yet our wind-up pump does not store water! When
we "charge" our wind-up pump, we send the charge (water) THROUGH THE PUMP, and
this stores energy by winding up the spring. Same with a battery: to "charge" a
battery, we send electrical charges THROUGH THE BATTERY and back out again. This
causes the chemicals on the battery plates to store energy, like winding up the
spring in our spring-powered water pump. See how "charging" and "charges" can
create a horrible mess of misunderstandings? When this mess gets into the
textbooks, and educators start teaching it to kids, the kids end up believing
that Electricity is too complicated for them to understand. Yet the fault does
not lie with the students!!!!
Another one: if you "charge" a capacitor, you move charges from one plate to
the other, and the number of charges within the device as a whole does not
change. Or from an engineer's perspective, you drive charge THROUGH the
capacitor, which causes potential across the plates to rise. But capacitors have
exactly the same total charge within them whether they are "charged" or not!
Whenever we take an electron from one plate, we put an electron onto the other
plate. When we speak of "charging" capacitors, we've suddenly stopped talking
about charge, and started talking about electrical energy. A "charged" capacitor
has quite a bit more energy than an "uncharged" one (but exactly the same
net-charge, and the same quantity of + and - particles inside it.) This basic
concept is very important in understanding simple circuitry, yet it is rarely
taught. The misleading term "charge" stands in the way of understanding. I
suspect that students are not the only ones being misled. Many teachers
misunderstand simple physics, and they believe that the purpose of a capacitor
is to store electric charge.
Think like this: both capacitors and inductors (coils) store ENERGY, and
neither one stores charge. Yet electric charge is the medium of energy storage
in both coils and capacitors. In capacitors, energy is stored in the form of
"stretched charge", or potential energy, while coils store energy in the form of
moving charge which contains kinetic energy. However, we don't put any charge
into a capacitor when we "charge" it, any more than we put charge into a
superconductor ring-inductor when we give the ring a "charge" of electromagnetic
energy.
During contact-electrification it is usually only the negative electrons which are moved. As negative particles are pulled away from the positive particles, equal and opposite areas of imbalance are created. In one place you'll have more protons than electrons, and this spot will have an overall positive charge. Elsewhere you'll have more electrons than protons, for an overall negative charge. You've not caused a "buildup", you've caused an imbalance, an un-cancelling, a separation. In fact, the science term for static electrification is CHARGE SEPARATION. The law of Conservation of Electric Charge requires that every time you create a region of negative charge, you must also create a region of positive charge. In other words you must create a separation of opposite charges. If you want to call it a "buildup of electrons", then you also need to call it a "buildup of protons," since you can't have one without the other.
All solid objects contain vast quantities of positive and negative particles
whether the objects are electrified or not. When these quantities are not
exactly equal and there is a tiny bit more positive than negative (or vice
versa), we say that the object is "electrified" or "charged," and that "static
electricity" exists. When the quantities are equal, we say the object is
"neutral" or "uncharged." "Charged" and "uncharged" depends on the sum of
opposite quantities. Since "static electricity" is actually an imbalance in the
quantities of positive and negative, it is wrong to believe that the phenomena
has anything to do with lack of motion, with being "static." In fact, "static
electricity" can easily be made to *move* along conductive surfaces. When this
happens, it continues to display all it's expected characteristics as it flows,
so it does not stop being "static electricity" while it moves along very
non-statically! In a high voltage electric circuit, the wires can attract
lint, raise hair, etc., even though there is a large current in the wires and
all the charges are flowing (and none of the electricity is "static.") And last,
when any electric circuit is broken and the charges stop flowing, they do *not*
turn into "static electricity" and begin attracting lint, etc. A disconnected
wire contains charges which are not moving (they are static,) yet it contains no
"static electricity!"
To sort out this craziness, simply remember that "static electricity" is not a quantity of unmoving charged particles, and "static electricity" has nothing to do with unmoving-ness. If you believe that "static" and "current" are opposite types of "electricity," you will forever be hopelessly confused about electricity in general.
The above issue affects the concepts behind the units of electrical
measurement. Energy can be measured in Joules or Ergs. The rate of flow of
energy is called Joules per second. For convenience, we give the name "power" to
this Joule/sec rate of flow, and we measure it in terms of Watts. This makes for
convenient calculations. Yet Watts have no physical, substance-like existence.
The Joule is the fundamental unit, and the Watt is a unit of convenience which
means "joule per second."
I believe that it is a good idea to teach only the term "Joule" in early
grades, to entirely avoid the "watt" concept. Call power by the proper name
"joules per second". Only introduce "watts" years later, when the students feel
a need for a convenient way to state the "joules per second" concept.
Unfortunately many textbooks do the reverse, they keep the seemingly-complex
"Joule" away from the kids, while spreading the "watt" concept far and wide!
Later they try to explain that joules are simply watt-seconds! (That's watts
TIMES seconds, not watts per second.)
If you aren't quite sure that you understand watt-seconds, stop thinking
backwards and think like this: Joules are real, a flow of Joules is measured in
Joules per second, and "Watts" should not interfere with these basic ideas.
There is a persistent 'rumor' that electric current exists only on the
surface of metals. This mistaken idea probably comes about through a
misunderstanding of the nature of electric charge. After all, when electric
charge is deposited onto a metal object, it distributes itself over the surface
of the object. It makes sense that, since charge is only on the surface of
metals, a flow of charge must take place only on the surface of metals, right?
Unfortunately, the word "charge" refers to two different things. When electric
charge is placed on a metal object, the added charge is just a drop in the
bucket compared to the amount of charge already in the neutral metal.
"Uncharged" wires contain an enormous amount of charge inside, even though they
may have "zero charge" on average. Are you confused yet?
All metals contain huge amounts of movable electrons. During an electric
current it is these electrons which flow. However, each electron is near a
proton, and so the metal is said to be "uncharged." In a wire, electric current
is a flow of "uncharged charge". Weird but true. Now if we were to place EXTRA
charge upon a wire, that would be like pouring a teacup into the ocean. The
"water level" would rise a tiny bit. Yet extra charges on a wire create a very
noticeable electrical imbalance (they attract lint, deflect electroscopes, make
sparks, etc.)
It isn't so strange that we might accidentally assume that the extra charges
are the only charges on the wire. Yet in reality, electric currents happen in
the "ocean" of the wire, and the extra "teacup" on the surface has little effect
on the charge flow. The charge flow (current) is not just on the surface, and
the whole "ocean" flows.
A second source of misunderstandings: during high frequency AC, the electric
current on the surface of a conductor is higher at the surface than it is within
the bulk of the metal. This is called the "skin effect." It is not very
important for thin household wires at 60Hz. Perhaps some people heard about the
Skin Effect but did not realize that it only works for very thick wires or for
high frequency AC. At extremely high frequencies, the current does flow as a
"skin" on the surface of large wires. For circuits involving high-current and
high-frequency such as radio transmitters, it makes sense to use copper pipes as
conductors. All the charge flow is on the surface of the conductors. All the
heating takes place on the surface, and not deep within the metal.
BAD:
Conductor - a material which allows charges to pass through
itself
BETTER:
Conductor - a material which contains movable electric
charges
If we place a Potential Difference across either air or a vacuum, no electric
current appears. This is sensible, since there are few movable charges in air or
vacuum, so there can be no electric current. If we place a voltage across a
piece of metal or across a puddle of salt water, an electric current will
appear, since these substances are always full of movable charges, and therefor
the "voltage pressure" causes the charges to flow. In metal, the outer electrons
of the atoms are not bound upon individual atoms but instead can move through
the material, and a voltage can drive these "liquid" electrons along. In salt
water, the individual sodium ions and chloride ions are free to flow, and a
voltage can push them so they flow as an electric current. If we stick our wires
into oil, there will be no electric current, since oil does not contain movable
charges.
If we were to inject charges into a vacuum, then we WOULD have electric current in a vacuum. This is how CRT's and vacuum tubes work; electrons are forcibly injected into the empty space by a hot filament. However, think about it for a second: it's no longer a vacuum when it contains a cloud of electrons! :) Maybe we should change their name to "electron-cloud tubes" rather than "vacuum tubes", since the electron cloud is required before there can be any conductivity in the space between the plates. (But vacuum tubes already have another name, so this would just confuse things. They are called "hollow-state devices." As opposed to "solid state devices?" Nuyk nuyk.)
Some scientists objected to Franklin's idea. They rightly pointed out that,
if Franklin was correct, then matter itself must be made up of negative
electricity, otherwise a rubber rod wouldn't become negative when Franklin's
electric fluid was removed from it. They noticed that Franklin was not proposing
a single kind of electric stuff. Instead Franklin was saying that two opposite
kinds of electricity exist, but only one of them is a movable "fluid." The other
kind would be solidly connected to the material of an object.
In hindsight we can see that Franklin was wrong. During electric currents in
batteries, currents in salt water, or in human flesh, the electric current is a
flow of both positive and negative ions moving in opposite directions. Two flows
of "electricity" take place in the same conductor. In your brain and nervous
system, electric current is a flow of positive and negative atoms going in
opposite directions. During electric currents in neon signs, in sparks,
lightning, etc., there is a flow of both positive ions and electrons. The same
is true for liquid metals. And when two materials are rubbed together, sometimes
positive or negative ions are transferred, and sometimes electrons are
transferred. In Franklin's language, two electric fluids do indeed exist, and
Franklin's "one fluid" theory is wrong.
Franklin was somewhat correct about two things. He was right about electric
current in solid (non-liquid) metals. During electric currents in wires, it's
the negative "electric fluid" which flows along, while the positive stuff
behaves as an "electric solid" and cannot flow. But melt the metal and this
frees up the positive atoms so that they can flow too. ALso, Franklin was right
in suspecting that, in some situations, "positive electricity" and "negative
electricity" differ greatly in mass. Protons are about 1800 times heavier than
electrons, and positive ions heavier still. But when electric current is a flow
of ions alone, the negative and positive ions can be very similar in mass, or
the negative ions can even be far heavier than the positive.
The complexity of electric charge was far greater than Franklin and his
contemporaries knew. Franklin was right about metals, but he was wrong about
conductivity in general. Modern science recognizes that positive particles can
flow, and recognizes the existence of both positrons and electrons, therefore it
rejects Franklin's "one fluid" theory of electricity.
The common belief that Franklin easily survived a lightning strike is not
just wrong, it is dangerous: it may convince kids that it's OK to duplicate the
kite experiment as long as they "protect" themselves by holding a silk ribbon.
Make no mistake, Franklin's experiment was extremely dangerous, and if lightning
had actually hit his kite, he certainly would have been killed.
Electric currents in electrolytes (such as wet dirt and human flesh) are
flows of electrified atoms. No electrons are flowing at all. When an electric
current is passing through a battery, it is not made of moving electrons, it is
made of moving atoms (ions), and each atom carries an imbalanced charge. A
similar thing happens when an electric current passes through the damp earth,
through the ocean, or through your body. If you receive an electric shock, no
electrons flowed inside you. These currents are flows of atoms. All the electric
currents in your brain and nerves are composed of moving sodium and potassium
atoms. No electrons! (MORE)
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