WHICH WAY DOES THE ELECTRICITY REALLY FLOW? (C)1996 William Beaty Electronics teachers and authors of textbooks are often chided for passing on an error to their students. Teachers promote the (wrong?) idea that electric current is a flow of positive particles in one direction, when supposedly its really a flow of negative electrons going the other way. In fact, the chiders are wrong. They labor under the misconception that Electricity is made of negatively-charged particles called electrons. This fundamental error leads most people to imagine that electric currents are always a flow of negative particles. Actually, in some conductors the electric currents are a flow of genuinely positive charges, while in others the flows are indeed negative particles. And sometimes the currents are both positive and negative particles flowing at once, but in opposite directions within the same conductor. We cannot arbitrarily decide which way the charges flow, since their true direction always depends on the type of conductive material. Electricity is more than just electrons Electricity is not made of electrons (or to be more specific, Electric Charge, which is sometimes called Quantity of Electricity, is not made of electrons.) Charge actually comes in two varieties: positive particles and negative. In the everyday world of electronics, these particles are the electrons and protons supplied by atoms in conductors. Physicists may additionally deal with other charged particles: muons, positrons, antiprotons, etc. But the electricity in common electrical devices is limited to positive protons and negative electrons. Because the negative particles carry a name that sounds like electricity, some beginners unfortunately start thinking that the electrons ARE the electricity, and they wrongly imagining that the protons (having a much less electrical name?) are not electrical. A few text and reference books even state this outright, saying that electricity is composed of electrons. Nope. In reality the electrons and protons carry electric charges of equal strength. If electrons are electricity, then protons are electricity too. Now everyone will rightly tell me that the protons within wires cannot flow, while the electrons can. Yes, this is true... but only true for metals. And its only true for solid metals. All metals are composed of positively charged atoms immersed in a sea of movable electrons. When an electric current is created within a solid copper wire, the electron sea moves forward, but the protons within the positive atoms of copper do not. However, solid metals are not the only conductors, and in many other substances the positive atoms *do* move, and they *do* participate in the electric current. These various conductors are nothing exotic. They are very common, they all around us; as close to us as they can possibly be. Non-electron Charge-flow For example, if you were to poke your fingers into the back of an old-style television set, you would suffer a dangerous or lethal electric shock. During your painful experience there obviously was a considerable current directed through your body. However, no electrons flowed through your body at all. The electric charges in a human body are entirely composed of positive and negative charged atoms or ions. During your electrocution, it was these charged atoms which flowed along as an electric current. The electric current was a flow of positive sodium and potassium atoms, negative chlorine, and numerous other more complex positive and negative molecules. During the electric current, the positive atoms flowed in one direction, while the negative atoms simultaneously flowed in the other. Imagine the flows as being like crowds of of tiny moving dots, with half the dots going in one direction and half in the other. The populations of little dots move through each other without any dots colliding. The postive atoms behave like flowing protons, but protons with entire atoms attached. The negative atoms behave like electrons which are dragging an entire atom along with them. So, inside human flesh ...which direction did the electric current REALLY go? Do we follow the negative particles and ignore the positive ones? Or vice versa, following the positives? There is a simple answer, but first... Batteries are another example of non-electron or ionic conductors. Whenever you connect a lightbulb to a battery, you form a complete circuit, and the path of the flowing charge is through the inside of the battery, as well as through the light bulb filament. Battery electrolyte is very conductive. Down inside the battery, within the wet chemicals between the two plates, the amperes of flashlight current appears as a flow of both positive and negative atoms. There is a powerful flow of electric charge going through the battery, yet no individual electrons flow through the battery at all. So, during the time when the charges flow between the two plates of the battery, whats its real direction? Not right to left, not left to right, but in both directions at once. About half of the charge-flow is composed of positive atoms, and the remaining portion is composed of negative atoms flowing backwards. Of course in metal wires outside the battery, the real particle flow is only from negative to positive. But inside the batterys wet electrolyte, the charge-flow goes in two opposite directions at the same time. (And if we built a circuit entirely out of hoses full of salt water, with no metal conductors used, then all the current would be bi-directional.) Two-way currents are common There are many other places where these kinds of positive/negative charge flows can be found. In the following list of devices-materials, the electric charges found within the conductors are a combination of movable positive and negative particles. During an electric current, both varieties of particles are flowing past each other in opposite directions. TWO-WAY POS/NEG ELECTRIC CURRENTS CAN EXIST IN: batteries human bodies all living organisms the ground the ocean the sky (ionosphere) electrolytic capacitors aluminum smelters liquid mercury and solder ion-based smoke detectors electroplating tanks fuel cells proton conductor membranes electrophoresis gels in research (esp. DNA testing) air cleaners, smoke precipitators particle beams the vertical sky current in the atmosphere gas discharge, which includes: electric sparks fluorescent tubes sodium and mercury arc streetlights neon signs the Earths Aurora lightning and corona discharges arc welders Geiger counter tubes thyratron tubes mercury vapor rectifiers This list is not so short. Again I ask you, what is the REAL direction of electric current? We cannot solve the problem by belittling it, or by pretending that two-way currents pertain only to something exotic, or pretend that its separate from everyday life. Our own nervous system is based on two-way currents. We dare not think that a current in a wire is real, while currents in human flesh somehow are not. Well, what is current? To gain some insight, lets examine the details. When trying to understand electric circuits and electrical measurements, we need a simple way to take measurements of the important entity named Electric Current. But to measure currents, wont we first need to measure how much of the current is composed of negative particles going one way, and of positive particles the other? Yes, but we only need this information if we want to know everything about the electric current. The flowing negatives and positives are usually not equal, and the speed of the positives in one direction is usually not the same as the speed of the negatives in the other. Electric current can be complicated! However, there is a cute trick we can pull in order to avoid having to look at the particles at all. And that trick holds the answer to the question. Electric currents produce three main effects: magnetism, heating, and the voltage drop across resistive conductors. These three effects cover almost everything we encounter in electronics. And these three effects dont care about the amounts of positive and negative particles, or about their speed, their mass, their charge, etc. If a hundred positive particles flow to the left per second, this gives exactly as much magnetism, heating, and voltage as a hundred negative particles flowing to the right per second. (Note: this is because reversing the polarity of the particles reverses the current, and reversing the particle direction reverses the current again! Two negatives make a positive.) Magnetism, heating, and voltage drop together represent nearly every feature thats important in everyday electrical circuitry. Therefore, as far as most electrical devices and circuits are concerned, it makes no difference if the current is made of positive particles going one way, or negative particles going the other... or half as many negatives flowing backwards through a crowd of half as many positives. Put simply, the Ampere doesnt care about the direction or speed of the flowing particles. So, in order to simplify our measurements and our mental picture of Electric Currents, we cut away the unused parts of the picture. We make the negative particles positive, then add their current to any positive particles which were flowing forward. We ignore their speed, and instead measure only the flow rate: the number of charges flowing per second. We stop thinking of current as being a flow of real physical particles. Instead we intentionally define electric current as being a flow of exclusively positive particles flowing in one particular direction. We dont care about the real polarity of the particles. We dont care about their speed, and we dont care about their number. We ignore both the chemical effects and the effects of the velocity and direction of moving particles. We ignore the collisions between positive and negative particles. All we care about is the total net charge which moves past a particular point in the circuit. The real charges are too complicated to deal with, and the added complexity gets us very little information as long as were only interested in voltage drop, magnetic fields, and heating. Particle-flow is real, Amperes are not Once we start ignoring the speed and direction of the charges, then we can easily build electrical instruments or amp meters which measure the Conventional Electric Current in terms of the magnetism which the charge-flow creates... or by the voltage drop which appears across a resistor, or by the temperature rise being created in a calibrated piece of resistance wire. These three types of meter will agree that a current is a current regardless of the particle polarities and flows. Then we can use these meters everywhere. In nearly every situation they will tell us all we could ever want to know about flows of charged particles in any circuit. An amp-meter might not be appropriate when used in an exotic physics experiment. It wont paint the correct picture when designing electron beams inside vacuum tubes, or ion flows in nerve fibers. It cannot detect real current, instead it only measures our conventionally-defined simple current. But for more than 99% of electricity and electronics, the direction of the particles is irrelevant, and an ammeter tells us the so-called real current while hiding the true particle flows. Or to put it simply: we pretend that electric currents are always composed of POSITIVE particles of unknown speed, so that any negative currents are defined as positive particles flowing backwards rather than negative particles flowing forwards. Confusing students for two hundred years We do cause some problems by choosing a positive charge convention. For example, what happens if we all spend many years thinking in terms of such simplified electric current? Might we eventually start believing that this oversimplified concept of positive electric current is REAL? Yet its not real, its simply one way to simplify things. Theres a genuine difference between the simplified picture versus the actual particle flows. The Amps would not quite match a visual picture of moving particles. But if we truely believe that the amperes are real, we might start to doubt the existence of flowing charges. We might start to see Electric Current itself as a sort of abstract, invisible, difficult-to-imagine thing. We might lose track of the facts that electric current is an actual flow of matter. We might lose track of the fact that there are real, visible particles flowing along inside that circuit, or that these particles have an actual average speed, mass, and direction. Because amperes are so incredibly useful, the simplified interpretation of Current takes over and becomes more real than reality. It allows us to understand parts of physical science which otherwise might be too complicated to imagine. But in letting the positive charges take over, some nagging questions are left behind, such as WHICH WAY DOES THE ELECTRICITY REALLY FLOW? (grin!)
Posted on: Mon, 14 Jul 2014 11:53:58 +0000
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