ELECTRICITY MISCONCEPTIONS IN TEXTBOOKS - - -William J. Beaty billbeskimo.com _________________________________________________________________ Accesses since 8/19/95: [INLINE] _________________________________________________________________ Add Your Own UNDER CONSTRUCTION Sorry if the following is a bit contentious at times. I wrote it in an attempt to get some things off my chest. If you keep watching this site, I'll probably clean it up and make it sound a bit more professional. Also, this file is still under construction and is being written, edited, corrected, etc. It does currently contain some mistakes of its own. I placed it online as a sort of 'trial by fire' in order to hear readers' responses and target weak or unclear sections for improvement. Please feel free to make comments to the author at billbeskimo.com -Bill B. ELECTRICITY DOES NOT EXIST The term "electricity" is a catch-all word with many meanings. Unfortunately these meanings are contradictory. There is no single substance or energy called "electricity." When we say "quantity of electricity," we could be talking about quantities of charged particles, or energy, or potential, forces, fields, net charge, current, power, or even about electrical phenomena. All of these are found under the definition of the word "electricity." Part of this problem would vanish if we used the word "electricity" only to designate a field of science or class of phenomena, in the same way we use the words "physics" or "optics." We do use it this way occasionally. But then we immediately turn around and do the equivalent of teaching our kids that the "optics" comes out of the light bulb and passes through the lens! Here are a couple of examples of errors caused by the contradictory meanings. In AC electric circuits the *charges* wiggle back and forth, but the *energy* moves continuously forward. This is analogous to the way that sound moves continuously forward while air wiggles back and forth. By applying contradictory definitions to the the term "electricity," we teach that electricity sits in one spot in the wires and wiggles, but at the same time electricity moves forward rapidly. Garbage! It's like saying that sound and wind are the same thing! And the error is directly tracable to the bogus "electricity" concept. Another: when a battery lights a bulb, we explain that the path of electricity is into, through, and back out of the bulb, and that none is used up. Then we say that electricity flows from the battery to bulb and is totally converted to light! So does the bulb consume "electricity" or does the "electricity" flow through it and back out again? As far as students are concerned, we've just told them that it does both at the same time! 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. Which is right? All and none, because the word "electricity" has multiple contradictory definitions. THE ELECTRICITY WHICH FLOWS IN WIRES IS NOT MADE BY BATTERIES OR GENERATORS Electric currents in copper wires are a flow of electrons, and these electrons comes from the copper atoms. Those electrons were in the metal 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 exists within the wires. A generator takes electrons in from one wire and simultaneously spits them out the other one, and at the same time it pushes them through the coil of wire within the generator and through the entire electric circuit. A generator or battery is a closed-loop pump, but it does not supply the substance being pumped. A generator is like your heart: it moves blood, but it does not create blood. When a generator stops or when the circuit is opened, all the electrons stop where they are, and the wires remain filled with electrons. But this isn't unexpected, because the wires were full of vast quantities of electrons at the start. THE "ELECTRICITY" FLOWING INSIDE OF WIRES DOES NOT FLOW AT THE SPEED OF LIGHT 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 flow incredibly slowly, at speeds on the order of centimeters per minute. It's the energy in the circuit which flows fast, not the electrons. 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 instantly througout the circuit. Energy and electrons are two distinct entities. Electrical energy is composed of electromagnetic fields. It does not travel along with individual electrons. The energy does not even flow inside the wires. ELECTRIC ENERGY IN A CIRCUIT DOES NOT FLOW IN A CIRCLE When you connect a light bulb to a battery, energy moves from the battery to the bulb. If this phenomena is examined in great detail, we find that the energy is composed of EM fields, that it moves as wave energy, that it exists only outside of the wires, and most importantly, that it TRAVELS ALONG BOTH WIRES on its way from the battery to the bulb. So when you plug a lamp into a wall socket, you should not imagine that the energy is a mysterious invisible entity travelling back and forth inside the wires. You should think of it as a mysterious invisible "tube"-shaped flow that comes out of the outlet, runs out along BOTH wires, and dives into the filament of the lightbulb. CHARGE The word "charge" has more than one contradictory meaning, so if you are using it, you are probably creating misconceptions. "Charge" refers to several things: to net-charge, to quantities of charged particles, and to "charges" of energy. For example, even when totally neutral, metals contain vast quantities of movable electrons. So, should we say that they contain zero charge, or that they contain immense quantities of charge? Or 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? Misuse of "charge" makes descriptions of electric circuits extremely confusing. Electric currents are a motion of neutralized charge, so if you teach that a wire is uncharged, and that current is a flow of charge, how can anyone make sense of a situation where a wire is uncharged yet contains an enormous flow of charge? Another one: if you charge a capacitor or a battery, you move charges from one plate to the other, and the device as a whole has exactly the same charge whether it's "charged" or not! When speaking of "charging" batteries or capacitors, we've suddenly started talking about energy, and a "charged" battery has quite a bit more energy (but exactly the same net-charge, and the same quantitity of particles) as an "uncharged" battery. This concept is very important in understanding simple circuitry, yet it is never taught, because the misleading term "charge" stands in the way. CONTACT ELECTRIFICATION OR "STATIC ELECTRICITY" IS NOT CAUSED BY FRICTION "Static electricity" 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 a surface and then peeled off, both the tape and the surface will become electrified. No friction was required. Of course if one of the materials is fiberous and does not give a very large footprint of contact area, the process of rubbing the material upon another can greatly increase the total contact area. But this rubbing is not the cause of electrification. "STATIC ELECTRICITY" IS NOT ELECTRICITY WHICH IS STATIC "Static electricity" exists whenever there are unequal amounts of positive and negative charged particles present. All solid objects contain vast quantities of positive and negative particles. 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 "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 effect 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 normal characteristics as it flows, so it does not stop being "static electricity" while it moves along very non-statically! And when an electric circuit is broken and the charges stop flowing, they don't turn into "static electricity" and begin attracting lint, etc. A quantity of unmoving charged particles does not constitute "static electricity." If you believe that "static" and "current" are opposite types of "electricity," you will forever be hopelessly confused about electricity in general. ELECTRIC CURRENT IS NOT A FLOW OF ENERGY Electric current is a slow motion of charged particles. On the other hand, electric energy is made of fields and it moves fast. Electric energy can move in a direction opposite to that of the electric current. Electric energy can even move continuously forward in the same wire where the direction of the current is alternating back and forth at high frequency. Electric energy is composed of electric and magnetic fields, and it exists in the space surrounding the wires. Electric current is very different, it's (usually) a flowing motion of electrons, and electrons are material particles. Electric current is a flow of matter, not of energy. When electric current exists in an electrolyte (in batteries, salt water, the earth, or in your body) it is a flow of charged atoms called ions, so there is no denying that it is a flow of material. Current is a matter flow, not an energy flow. ELECTRIC POWER CANNOT BE MADE TO FLOW Power is defined as "flow of energy." Saying that power "flows" is as silly as saying that the stuff in a moving river is named "current" rather than of "water." Water is real, water can flow, flows of water are called "currents," but we shouldn't make the mistake of believing that "currents" are a substance. Energy is sort of like a stuff, and it can flow along. When electric energy flows, it's flow is called electric power. But electric power has no existance of its own. Electric power is the flowing motion of another thing. Electric power is an energy current. This impacts 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 this rate of flow the name "power," and we measure it in terms of Watts. Yet Watts have no physical substance-like existance. The Joule is the fundamental unit, and the Watt is a unit of convenience. It is probably a good idea to teach only the term "Joule" in early grades, to entirely avoid the "watt" concept, and to only introduce it years later when the students feel a need for a convenient way to state the energy-flow-per-unit-time concept. Unfortunately many textbooks do the reverse, and keep the seemingly-complex "Joule" away from the kids, while spreading the "watt" concept far and wide! LIGHT AND RADIO WAVES DO NOT TRAVEL AT 186,000 MILES PER SECOND They only travel at 186,000 miles per second while in a perfect vacuum. Light travels a bit slower in the air, and it travels 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," and light (and electrical energy) can travel at many different speeds. ELECTROMAGNET COILS DO NOT USE UP ENERGY TO MAKE MAGNETISM Coils only require energy to initially create a magnetic field. They also require energy to defeat electrical friction when a field is being maintained. But if the friction is removed, the magnetic field can exist continuously without energy input. If frictionless (superconductive) wire is used, a coil can be momentarily connected to an energy supply to create the field, then the supply can be removed and the field will continue forever. Voltage STORM CLOUDS ARE NOT CHARGED BY FRICTION Some books claim that the separated charges in thunderstorms comes about when clouds rub against each other, or when the rain moves through 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 been yet proved true, and all have problems. Here's one: in a mixture of hail and rain, the ice and water become oppositely electrified through contact. The large hail then falls faster than the small raindrops, so two large regions of opposite charge are gradually created within the cloud, one above the other. BEN FRANKLIN'S KITE WAS NEVER STRUCK BY LIGHTNING Many people believe that Ben Franklin's kite was hit by a lightning bolt, and this is 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! What Franklin actually did was to show 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 charged, and the hairs on the twine stood outwards. The twine was then used to charge 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 charges, and 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 NOT MADE OF ELECTRONS Electric current in metals is a flow of electrons. But electric current doesn't only flow in metals. It also flows in electrolytes. Electric currents in electrolytes are flows of electrified atoms. So when an electric current is passing through a battery, it is made of moving atoms, not of moving electrons. A similar thing happens when a current passes through the earth, the ocean, and your body. All the electric currents in your brain and nerves are composed of moving sodium and potassium atoms!