Source www.austincc.edu/wkibbe/truth.htm from
Many authors bemoan the fact that Ben Franklin labeled "resinous electricity" as negative, and "vitreous electricity" as positive. By choosing the polarities this way, Franklin forces us to say that electrons carry a charge of negative electricity. As a result, we must name the electric currents in metals as flows of NEGATIVE charge rather than positive charge.
Did Franklin make a mistake? ABSOLUTELY NOT. In fact it's a blessing, since these flows of negative charge aren't inherently confusing. Franklin's choice of polarity fortunately helps reveal the true source of confusion: common and widespread misconceptions about electrons and "electricity".
If Franklin had instead chosen the electrons to be positive, then we could more easily avoid confronting the real problem. We could ignore the misconceptions, and we'd end up with only illusion of understanding. Yet we'd also have all sorts of niggling unanswered questions caused by the misconceptions.
The solution isn't just to ignore our discomfort and pretend that we understand electricity. The solution is to confront the source of our discomfort. If we dislike negative currents or find them to be confusing, it's because our misconceptions are fighting back. What misconceptions? Here is a list:
These seven statements are wrong. We have Ben Franklin to thank for rubbing our noses in this fact. If he had chosen the polarities so that the electrons came out positive, we'd be much more comfortable. We might never ever notice the problem.
Here are the corrections for the above seven mistakes:
Also plasmas can have positive electric currents as well as negative: for example neon signs, fluorescent lights, camera flashes, and sparks of all kinds. There are some conductors where the current is a flow of positive hydrogen ions, +H ions, otherwise known as protons. One common "proton conductor" is ice. Others are used as solid electrolytes in exotic batteries and more recently in tiny fuel cells.
I thank Ben Franklin for the discomfort and the controversy he caused by giving the "wrong" polarity to electrons. Without his "mistake," students and teachers would be much more comfortable in their misconceptions, and they might never search for answers.
I try to take my own advice: I always imagine that electric currents in circuits are NOT flows of electrons; instead they are flows of "charges" or "charged particles". Unless we know what kind of conductor is involved, we CANNOT know whether an electric current is composed of moving electrons, or electrons and positive atoms, or of positive and negative atoms. For example, if you receive an electric shock, no electrons flowed through your body.
THE "ELECTRICITY" WHICH FLOWS IN WIRES IS SUPPLIED BY BATTERIES OR GENERATORS? -----Wrong.
Electric currents in copper wires are a flow of electrons, but these electrons are not supplied by batteries. Generators do not 'generate' them. Instead they come from the wire. In copper wire, copper atoms supply the flowing electrons. The electrons in a circuit were already there before the battery was connected. They were even there before the copper was mined and made into wires! Batteries and generators do not create these electrons, they merely pump them, and the electrons are like a pre-existing fluid that is always found within all wires. In order to understand electric circuits, we must imagine that all the wires are pre-filled with a sort of "liquid electricity".
To clarify this, get rid of the battery. Instead, use a hand-cranked generator as your power supply. Ask yourself exactly where the flowing "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. It also pushes them through the rest of the circuit.
Unlike the situation with a battery-powered circuit, all we have here is wires. Where is the source-point of this flowing "electricity"?
When we include the generator in the circuit, we find that the circuit is a continuous closed loop, and we can find no single place where the "electricity" originates. A generator or battery is like a closed-loop pump, but it does not supply the substance being pumped. But weren't we all taught during grade-school 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. That's what a conductor is, it's a material which contains 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.
"ELECTRICITY" IS A PHENOMENON COMPOSED OF ENERGY? ------ Wrong.
Actually, "Electricity" does not exist. The term "electricity" is a catch-all word with many meanings. Unfortunately these meanings are contradictory, and this leads to the unsettling fact that there is no single substance or energy called "electricity". When we say "quantity of electricity," we could be talking about quantities of charged particles.
But we could also be talking about quantity of energy, quantity of current, or potential, forces, fields, net charge, power, or even about electrical phenomena. All of these are found as separate dictionary definitions of the word "electricity".
But current is not power, particles are not fields, and charge is not energy. "Quantity of Electricity" is a meaningless concept because of the contradictory definitions of the word "electricity".
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.
Another: There are two forms of electricity, positive electricity and negative. NO, the two forms of electricity are static and current. NO, there are many forms of electricity: triboelectricity, bioelectricity, myoelectricity, piezoelectricity. NO, electricity is a single form of energy called Electromagnetism. NO, electricity is power, it is watts, not energy.
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 class of 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.
ELECTRICITY IS A TYPE OF EVENT?--- NO.
Scientists originally had a very clear meaning for the word "electricity". It meant "charge". They would say that electrons carry negative electricity, and protons carry positive electricity. They would say that an electric current is a flow of electricity. Unfortunately the meaning of the word became corrupted in the early 20th century when electric companies started selling electrical energy.
They called this energy by the name "electricity". But this is a serious problem. When you turn on the lights in your home, the charge inside the wires wiggles back and forth and does not flow forwards, while the energy moves continuously forwards at almost the speed of light. So does electricity sit in one spot and vibrate? Or does electricity flow forwards rapidly? Clearly charge is not energy, so the word "electricity" became a single name for two very different things. Bad move.
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" had long been used to name all 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 different subject headings in science books. They are different kinds of electrical occurrences, 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 also wrong.
They are attempting to add yet another definition to the growing list! 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 figure out what "electricity" really is, we will keep spreading the confusion.
The only honest move is to stop covering up the problem. We should perform an act of painful honesty, and admit that we've been accidentally misleading generation after generation of students by teaching them about the wonderful substance/occurrence/energy called "electricity" which doesn't really exist.
ELECTRONS IN WIRES JUMP FROM ATOM TO ATOM DURING A CURRENT? ------ Wrong.
When individual atoms of copper are brought together to form a bulk metal material, something unexpected happens. The outer electron of each copper atom leaves its parent atom. Rather than orbiting single atoms, the outer electrons all begin "orbiting" around and among ALL the atoms in the metal. In a sense, the metal's electrons are "jumping" from atom to atom all the time, even when there is no electric current applied. As a result, metals act like a solid sponge which has been soaked with "liquid charge". That's what makes wires so wonderful: they act like pre-filled pipes. They are filled with "liquid electrons".
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 sea 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.
THE "ELECTRICITY" INSIDE OF WIRES MOVES AT THE SPEED OF LIGHT? ------- Wrong.
In metals, electric current is a flow of electrons. Many books claim that these electrons flow at the speed of light. This is incorrect. Electrons actually flow quite slowly, at speeds on the order of centimetres per minute. It's the energy in the circuit which flows fast, not the electrons. Metals are always full of movable electrons, and when the electrons at one point in the circuit are pumped, electrons in the entire loop of the circuit are forced to flow, and energy spreads almost instantly throughout the entire circuit.
This happens even though the electrons move very slowly.
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 about electron speed. Here's another way to understand the problem. Think of sound waves. When we talk, do the vocal cords spew out air molecules? No.
Do these molecules zoom out of our mouths at 720 MPH, fly across the room, then crash into waiting eardrums? NO! Air molecules are not sound waves. It's the sound waves that move quickly, not the air molecules. In reality the air barely moves at all, instead the air vibrates back and forth while the sound waves race through the air.
The same is true of AC electric circuits: the wires are already full of electrons just as the room is already full of air. And when the electrical energy flies along the wires at the speed of light, the electrons do not follow it. Instead the electrons sit in one place and vibrate.
Many people have questioned whether it is wrong to teach our kids that electrons move at the speed of light. Well, ask yourself whether it's wrong to teach kids that sound is actually wind, and that sound is made of air molecules that fly through empty space at 720 mph. Yes, it's terribly wrong. People will have almost no understanding of sound at all if they think that sound is made of flying molecules. We need to know that sound is a kind of wave. If we don't, then we have a learning barrier, and our understanding of sound stops dead. And people will have almost no understanding of electricity at all if they think that electrons fly through empty wires at the speed of light. We need to know that electrical energy is a kind of wave. If we don't know this, then we have a very serious learning barrier. Only then can learning continue.
THE ELECTRIC ENERGY IN A CIRCUIT FLOWS IN A CIRCLE? ----- Wrong.
When you connect a light bulb to a battery, Electrical Energy moves from the battery to the bulb. This is a one-way flow. The battery loses energy and the bulb gains it.
Then the energy received by the bulb is turned into light. If this phenomenon is examined in great detail, we find that electrical energy is composed of waves travelling along columns of electrons inside the wires, and the energy itself is contained in electromagnetic fields connected to those electrons. We find that it moves as wave energy, that it exists only outside of the wires, and most importantly, that it TRAVELS ONE WAY ALONG BOTH WIRES on its trip from the battery to the bulb. The energy did not travel in a circle. So, when you plug a lamp into a wall socket, you shouldn't imagine that the AC energy is a mysterious invisible entity traveling back and forth inside the wires.
Instead you should think of AC energy as a mysterious invisible flow that comes out of the outlet, runs along the outside of BOTH wires, then dives into the filament of the light bulb. Your electric company is sending out long "sausages" of electrical energy, the wires are guiding them, and your appliances are absorbing them.
THE TWO KINDS OF ELECTRICITY ARE "STATIC" AND "CURRENT?" ------ No.
Static and Current are two ways in which electrical charges can behave. If we said that Electrical Science is divided into two fields of research called Electrostatics and Electrodynamics, we would be correct. But aren't there different kinds of electricity? Well please realize that the study of WATER is divided into Hydrostatics and Hydrodynamics, yet we don't go around claiming that "current water" is one type of water, while "static water" is a different type of water. The same applies to electric charges.
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 electro statically charged... but the charges are NOT STATIC. Yet the wire will cause hair to rise, and it can attract fur or lint... but 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 key is the separation of the charges, 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, so it falls under the subjects of "hydrostatics" and "hydrodynamics" simultaneously. 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".
CURRENT ELECTRICITY IS THE OPPOSITE OF STATIC ELECTRICITY? ------ Wrong.
"Static" appears whenever the negative charges within matter are separated from the positive charges. "Current" appears whenever the negative charges within matter are made to flow through the positive charges (or when positive flows through negative.) These are two separate kinds of events, they are not opposites.
"Static" is a separation; it is a stretching-apart, and it really has little to do with anything remaining static or stationary.
"Current" is a flowing motion. It has little to do with the separation of opposite charges.
"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".
THE STUFF THAT FLOWS THROUGH WIRES IS CALLED 'ELECTRIC CURRENT'? ---- Misleading!
Most textbooks discuss a substance or energy called "current". They constantly talk about flows of current. However, here's a pointed question: WHAT FLOWS IN RIVERS? Is it water, or is it "current"? If I fill a bucket from the faucet, is my bucket full of "current"? No! The same idea applies to electricity: electric current is a flowing substance, but the name of the substance is not "current".
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.
ELECTRIC CURRENT IS A FLOW OF ENERGY? --------Wrong.
Electric current is actually a flowing motion of charged particles. The words "Electric Current" mean the same as "charge flow". Electric current is a very slow flow of charges. On the other hand, electric energy is different. It is made of waves in electromagnetic fields and it moves VERY rapidly.
Electric energy moves at a different speed than electric current, so obviously they are two different things flowing in wires at the same time. Unless we realize that two different things are flowing, we won't understand how circuits work.
Indeed, we will have little grasp of basic electrical science.
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!
ELECT. LEAVES ONE BATTERY PLATE, AND THEN RETURNS TO THE OTHER? ----------- Not quite.
In a simple circuit, the actual path of electric current is THROUGH the battery. Some books imply (or even state outright) that, whenever a battery is connected in a complete circuit, the charges flow only in the wires, and that no charges flow in the chemicals between the battery plates. This is wrong. These books often contain a diagram of a battery, wires, and a light bulb. The diagram shows the current in the wires, but it shows no current going THROUGH the battery.
This is wrong.
In any simple electric circuit, the path of the electric current is a complete circle. It is like a drive belt, 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?
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.
ELECTRIC ENERGY IS CARRIED BY INDIVIDUAL ELECTRONS? ---- Wrong.
Some books teach that, in a simple battery/bulb circuit, each electron carries energy to the bulb, deposits its energy in the hot filament, and then returns to the battery where it's re-filled with energy. This is wrong. Some books give an analogy with a circular track full of freight cars waiting to be filled with coal.
This picture is wrong too. The energy in electric circuits is not carried by individual electrons. Instead the electrons move very slowly while the electrical energy flows rapidly along the columns of electrons. The energy is carried by the circuit as a whole, not by the individual charged particles.
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 wheel, your hand injects energy into the entire 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 the energy would be forced to travel only as fast as the rubber.
Your "friction" hand wouldn't experience any friction until those magically 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. In this way it injects energy into the WHOLE CIRCUIT all at once. As soon as the battery moves the electrons, the distant light bulb 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 teaching it to their students! After all, the kids instantly grasp the "freight cars with coal" story since it is very visible and it offers a sensible explanation.
What more can we ask? Yet there, is a serious problem here: electrons flow slowly, and in AC circuits they don't flow at all, instead they wiggle.
In order to really understand electric circuits in the more advanced classes, a student must UNLEARN the seductive 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 level. Yes, if the kids will never have any need to understand how electricity REALLY works, then the freight-cars analogy is fine. The kids can memorize it, teachers can test them for it, and everybody is happy.
But if the kids grow up to become scientists and engineers and technical people, then the freight-cars analogy causes them harm. (Unfortunately, it only causes FUTURE harm, so the K-6 educators never encounter the negative effects of the misconceptions they've installed in the kids' minds.) What if you were using the "freight cars w/coal" analogy, but you also had to explain how "AC" works? In that case the freight cars are moving back and forth but not progressing forwards.
How can they deliver their coal to the far end of the track? I suspect that teachers encounter this problem, and rather than recognizing that "freight cars" is a misconception, they instead pile another misconception: the wrong idea that electrons in wires flow at the speed of light. After all, if the coal-filled freight cars travelled INSTANTLY to the far end of the track, then dumped their coal, then travelled instantly back, that would be alternating current. Right?!! But electric current is actually a very slow flow of charges, and during AC those "freight cars" only wiggle back and forth a few feet on their tracks.
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 will heat it up. Energy can essentially 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.
The "filled freight cars" 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...
How about an analogy regarding this analogy (grin!) How do sound waves work? Ask yourself this. 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 eventually 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: sound is carried by waves in the air, not by air molecules launched at immense velocities out of your mouth. And any kid who believes this "launched molecules" sound explanation will have terrible difficulties should they ever have need to understand how sound REALLY works.
All of this is an analogy for wires and circuits: electrical energy is wave energy; electrical energy moves along the columns of electrons like sound moves through the air, and when electrical energy flows across a circuit, the electrons DON'T flow along with it.
BATTERIES STORE CHARGE AND THIS CHARGE FLOWS IN WIRES? ------- No.
The word "charge" has more than one meaning, and the meanings contradict each other. The "charge" in a battery is energy (chemical energy), while the "charge" that flows in wires is part of matter, it is electron particles. And those wires, though full of charge... are neutral and uncharged! The term "charge" refers to several different things: to net-charge, to quantities of charged particles, and to "charges" of energy. If you are not very careful while using the word "charge" in teaching, you might be spreading misconceptions.
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", its 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.
"STATIC ELECTRICITY" IS CAUSED BY FRICTION? -NO
"Static electricity" is not caused by friction. It appears when two dissimilar insulating materials are placed into intimate contact and then separated. All that's required is the touching.
For example, when adhesive tape is placed on an insulating surface and then peeled off, both the tape and the surface will become electrified. No rubbing was required. Or when a plastic wheel rolls across a rubber surface, both the surface and the wheel become electrified.
Intimate contact is sufficient, and no rubbing is needed. Of course if one of the materials is rough or fibrous, it does not give a very large footprint of contact area.
In this case the process of rubbing one material upon another can greatly increase the total contact area. And the heating of the fibers can make the materials even more electrically "dissimilar", which aids the charge-separation process. But this rubbing is not the cause of the electrification.
"STATIC ELECTRICITY" IS A BUILDUP OF ELECTRONS? -------Wrong.
It is not a buildup of anything; it is an IMBALANCE between QUANTITIES of positive and negative particles already present.
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.
"STATIC ELECTRICITY" IS ELECTRICITY WHICH IS STATIC? ------ Wrong.
"Static electricity" exists whenever there are unequal amounts of positive and negative charged particles present. It doesn't matter whether the region of imbalance is flowing or whether it is still.
Only the imbalance is important, not the "staticness". To say otherwise can cause several sorts of confusion.
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 phenomenon 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 its 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.
ELECTRIC POWER FLOWS FROM GENERATOR TO CONSUMER? ---- Wrong.
Electric power cannot be made to flow. Power is defined as "flow of energy". Saying that power "flows" is silly. It's as silly as saying that the stuff in a moving river is named "current" rather than named "water". Water is real, water can flow, flows of water are called currents, but we should never make the mistake of believing that water's motion is a type of substance. Talking of "current" which "flows" confuses everyone. The issue with energy is similar. Electrical energy is real, it is sort of like a stuff, and it can flow along.
When electric energy flows, the flow is called "electric power". But electric power has no existence of its own. Electric power is the flow rate of another thing; electric power is an energy current. Energy flows, but power never does, just as water flows but "water current" never does.
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.
LIGHT AND RADIO WAVES TRAVEL AT 186,000 MILES PER SECOND? ------ No.
They only travel at 186,000 miles per second while in a perfect vacuum. Light waves travel a bit slower in the air, and they travel LOTS slower when inside glass. Radio waves move much slower than 186,000 miles/sec when they travel within plastic-insulated coaxial cable.
The term "speed of light" is misleading, because the complete term actually reads "speed of light in a vacuum". There actually is no set "speed of light" because light waves and radio (and electrical energy) can travel at many different speeds depending on the medium through which the waves propagate.
ELECTROMAGNET COILS USE UP ENERGY TO MAKE MAGNETISM? ------ Not right.
Sustaining a magnetic field requires no energy. Coils only require energy to initially create a magnetic field. They also require energy to defeat electrical friction (resistance); to keep the charges from slowing down as they flow in wires.
But if the resistance is removed, the magnetic field can exist continuously without any energy input. If electrically frictionless superconductive wire is used, a coil can be momentarily connected to an energy supply to create the field. Afterwards the power supply can be removed and both the current and the magnetic field will continue forever without further energy input.
ELECTRIC CHARGES ONLY FLOW ON THE SURFACES OF WIRES? ------- Wrong.
During a Direct Current in a simple circuit, the flow of charges takes place throughout the whole wire. The flow is not just on the surface. If the level of current is very high, then the wire will become hot, and the current will heat up the inside of the wire as well as its surface. Thin hollow pipes make poor conductors; their electrical resistance is too high. To avoid overheating the metal we should use thick solid bars instead.
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.
ELECTRIC CHARGES ARE INVISIBLE? ------ No.
Electric charges are very visible, even though their motion is not. When you look at a metal wire, you can see the charges of electricity which flow during electric currents. They are silvery/metallic in color. During an electric current, it is the "silvery" stuff that flows along, (under construction)
ATOMS HAVE EQUAL NUMBERS OF ELECTRONS AND PROTONS? ------- NO
Students misunderstand how electric circuits work. One reason for this is that they think the electrons in a metal are trapped on individual metal atoms. They also think that an applied voltage is needed to "free" the electrons and to change metal into a conductor.
They aren't aware that the "sea of electrons" exists inside metal all the time. I suspect that this is part of a more general misconception that all atoms in a material are always neutral. This is wrong because ALL CONDUCTORS contain charged, movable particles. The very definition of "conductor" is "a material which contains mobile charges".
If all atoms were truly neutral, then conductors could not exist.
For example, a metal is made of positively charged atoms immersed in a sea of loose electrons. Apply a voltage to a metal, and its electrons begin flowing. Salt water is full of positive and negative ions. Glowing gas (fluorescent lights, neon signs, sparks) is full of movable electrons and movable positive ions.
These three are the most common conductors, and they owe their conductivity to the presence of movable charged particles which occur naturally.
A "CONDUCTOR" IS A MATERIAL WHICH ALLOWS CHARGE TO PASS THROUGH IT? ------ Not exactly.
The scientist's definition of the word "conductor" is different than the one above, and the one above has problems. For example, a vacuum offers no barrier to flows of electric charges, yet vacuum is an insulator. Vacuum is NOTHING, so how can it act as a barrier to electric current?
Also, there is a similar problem with air: electric charges placed into the air can easily move along, yet air is an insulator.
Or look at salt water versus oil. Oil is an insulator, while salt water is a conductor, yet neither liquid is able to halt the flow of any charges which are placed into it. How can we straighten out this paradox? Easy: use the proper definition of the word "conductor".
Conductor - a material which allows charges to pass through itself
Conductor - a material which can support an electric current
Conductor - a material which contains movable electric charges
Conductor - like a pipe which is already full of water
Insulator - like a pipe with frozen liquid; a pipe plugged by ice
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 therefore 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"?
HUMID AIR IS CONDUCTIVE? ------ Mistake.
Electrostatic experiments don't work very well under humid conditions. Some books state that the water vapor in the air makes the air conductive. Wrong. In reality the problem is caused by the liquid water adsorbed on surfaces.
In order to make the air conductive, we'd have to fill it with movable charged particles.
Evaporated water is not made of charged particles (ions), it's made of neutral molecules, so the high humidity does not significantly affect the conductivity of the air. Even suspended water droplets (fog) does not significantly affect humidity.
For fog to be conductive, the individual droplets would have to be electrically charged. However, during humid conditions most insulators develop a surface layer of conductive liquid made of water mixed with contaminants (including dissolved salts which makes this layer of water conductive.) If you find that you can't separate any charges by rubbing a balloon on your head, it's because the humid air has made the balloon and the hair very slightly damp.
The air remains nonconductive, but surfaces of insulators become conductive when damp. Conductive surfaces don't separate any opposite charges when rubbed together. Cure this by warming them (drying them) with a blow-dryer. If a pair of insulators is sufficiently dry, it will "generate charge" even under humid conditions. If conductive air was the culprit, this couldn't work.
ELECTRICITY IS WEIGHTLESS? ----- Nope.
If by 'electricity' we mean the electrons, then 'electricity' is not weightless. Take a copper wire for example. Each atom weights about 115,000 times larger than the weight of an electron. If each atom supplies one electron to the "electric fluid" sea, then that sea is very light, but it is not weightless. The flowing "electricity" weighs about a hundred thousand times less than the copper metal. It's like a low pressure gas rather than like a liquid (but never forget that a gas is still matter!) One KG of copper would contain about ten milligrams of the movable electron-stuff which can flow as an electric current.
THE "TWO FLUIDS" THEORY WAS DISPROVED? Not exactly.
In the early days of electrical science, researchers were sure that there were two kinds of electricity: "vitreous electricity" and "resinous electricity," later to be named positive and negative electricity.
They imagined that these represented two kinds of "electric fluid" which were somehow created by rubbing various materials together.
Ben Franklin proposed a different concept: he imagined that there was only one kind of electric fluid, positive electricity and believed that "negative electricity" was simply a lack of electric fluid.
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.
STORM CLOUDS ARE ELECTRIFIED BY FRICTION?-------- No.
Some books claim that the separated charges in thunderstorms come about because the clouds rub against each other, or because the falling rain rubs against the air. This is not correct. In fact, the true explanation for storm electrification is unknown. There are several possible explanations, but none of them has yet been accepted by scientists, and all the theories have problems. Here's one current theory:
In a mixture of rain and half-melted hail, the ice and water become oppositely electrified through contact. The large hail then falls faster than the small raindrops and spray. Two large regions appear in the cloud, a lower one that's made of hail, and an upper one that's made of rain.
These regions contain opposite imbalances of electric charge.
So, what caused the clouds to become electrified? Contact between dissimilar materials, followed by wide separation of those materials.
BEN FRANKLIN'S KITE WAS STRUCK BY LIGHTNING? -------- Never happened!
Many people believe that Ben Franklin's kite was hit by a lightning bolt, and think that this was how he proved that lightning was electrical. A number of books and even some encyclopedias say the same thing.
They are wrong. When lightning strikes a kite, the spreading electric currents in the ground can kill anyone standing nearby, to say nothing of the person holding the string! So what did Franklin actually do? He showed that a kite would collect a tiny bit of electric charge out of the sky during a thunderstorm. Electric leakage through the air caused his kite and string to become electrified and so the hairs on the twine stood outwards. Twine is slightly conductive, so the imbalanced charge spread to all parts of the kite string. Franklin used the twine to electrify a metal key, and tiny sparks could then be drawn from the key. (He used a metal object because sparks cannot be directly drawn from the twine, it's not conductive enough.) This suggested that some stormclouds carry strong electrical net-charge. It IMPLIED that lightning was just a large electric spark.
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.
ELECTRICITY IS MADE OF ELECTRONS? ----Wrong.
It's true that electric current in metals is a flow of electrons. But there are many other conductors besides metals, and sometimes the current is not made of moving electrons. Electric currents can also appear in electrolytes, or in plasma.
When an electric current creates the glowing plasma within a neon sign, electrons flow in one direction, while positively charged ATOMS flow in the other.
There is an electron flow in the glowing gas, but part of the total electric current is also made of flowing atoms.
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!
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