The "real" direction of electric current

Discussion in 'General Electronics Chat' started by wbeaty, Jul 14, 2005.

  1. wbeaty

    Thread Starter New Member

    Jul 14, 2005
    1
    0
    Heh. I quite enjoyed your essay:
    BASIC CONCEPTS: Conventional vs. Electron flow
    http://www.allaboutcircuits.com/vol_1/chpt_1/7.html


    I have a couple similar ones posted on my own site:
    Which way does "electricity" REALLY flow?
    http://amasci.com/amateur/elecdir.html

    Too bad Franklin said electrons were negative?
    http://amasci.com/miscon/eleca.html#frkel


    Which way does electric current really go? This is a good topic for making people fly off the handle and starting flamewars. I'm glad to see that you've lived on both sides of the great divide. People don't usually want to kill the infidels when they've been an infidel themselves. :)

    Me, I eventually settled on the positive-flow Religion. Why? Because it's part of the physics which underlies all of electronics, though this point is rarely discussed.

    The central concept in physics is that, whenever we use "amperes" and "current," we don't care about the velocity of the flowing particles. They could be a few particles moving fast, or vast number of particles moving slow. An ammeter can't tell the difference. They could be positive particles moving forward, or negative particles going the other way. An ammeter has no clue. And in many common conductors such as battery acid and human flesh, the current is composed of both positives and negatives going in opposite directions at the same time. An ammeter won't know this is happening. The speed and direction of the charges is irrelevant because it doesn't affect the magnetic fields caused by the current, nor does it affect the amount of heating produced in a resistor, nor the amount of chemical change in a battery or electroplating tank.

    In other words, when an electric current is made of unknown charges, an ammeter sums them together and calls them "current." (Well actually it reverses the direction of the negatives first, so that the backwards electrons would add up to give exactly the same amperes as forward protons.) In other words, "current" as we commonly measure it is not a flow of real particles. Instead, the amps are a characteristic of the flowing particles; a characteristic which hides their velocity and hides their polarity and hides their direction.

    What direction does this "characteristic" have?

    The direction is the simple and obvious one: an arrow that points in the mathematically positive direction. So, if electrons are flowing along, their "current arrow" must point backwards because the electrons are negative. You just can't get away from that effect. Electrons and protons give opposite currents when they flow in the same direction, so they must have opposite arrows. If you draw some arrows on a circuit diagram, and those arrows show which way an electron would travel, then those arrows don't show electric current, instead they show particle flow. Those arrows are negative and they show the opposite of an electric current.

    Psychology obviously enters into this stuff. Most beginning students are "concrete thinkers" who don't want abstractions. They want to know the real direction of the actual particles. I find that many textbooks don't tell students the truth. Their authors fall into dishonesty in one of two ways: some pretend that all current is positive charges. They expect their students to just accept this without complaint. Or, the authors will pretend that all current is electrons. They concentrate on wires and vacuum tubes while carefully avoiding any situation where positive particles actually flow along.

    The real truth is different.

    Many conductors contain movable positive and negative ions, and these flow in opposite directions. That's how salt water, battery acid, and human flesh work. The ionized gases in flourescent tubes and neon signs contain moving positive atoms as well as moving electrons. Liquid metals contain moving positive atoms as well as moving electrons. A few conductors even support proton-only currents. These are the solid electrolytes often used in Fuel Cell membranes (search on keywords "proton conductor" for thousands of google hits.) Solid ice is also a proton conductor. And then we have the semiconductors with their four types of current: majority and minority carriers, each with holes and electrons.

    How the hell can we simplify this stuff? It would be dishonest to cover it up and pretend that all currents are made of electrons, or that all currents are "conventional positive flow." The students want the truth, so we should just come clean and give it to them. Show them what happens when a proton conductor is connected to a metal rod while a current is passed along the junction. Examine the cases where positives and negatives seem to meet and cancel out... or where a junction between conductors seems to spew out infinite amounts of positives and negatives in opposite directions. Let them try to understand a motor where the coils are wound with salt water hoses or neon sign tubes.

    After students have confronted the nasty complexity of real-world conductors, THEN they'll understand the need for "wrong" concepts like "Amperes" where the particle velocity is ignored, and "current" where the direction of flow is irrelevant.
     
  2. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6


    The only 100% accurate model of the universe is the universe itself.

    If a simple model works adequately for a given application, then there is no point in using a more complex model. I don't bother with forrier analysis when driving an H-Bridge with a 555.

    It is of course good to know about the more complex models, should they be needed for some other application. I just might pull out forrier analysis when designing a bandpass filter.

    Electron flow theory works fine and dandy as a model for many applications. Hole flow theory works better for others. Different models for different applications will also work better or worse for different individuals (ie: I find antenna theory far more easy to grasp when thinking in terms of hole-flow).

    The critical thing in all this is to remember that the model is not the universe - the map is not the territory. It is this concept that the student must "keep simmering on the back burner." By being flexible in one's thinking, one can more easily adapt to new models.

    <!--QuoteBegin-wbeaty
    @Jul 14 2005, 12:41 AM
    After students have confronted the nasty complexity of real-world conductors, THEN they'll understand the need for "wrong" concepts like "Amperes" where the particle velocity is ignored, and "current" where the direction of flow is irrelevant.
    [post=9052]Quoted post[/post]​
    [/quote]

    Here I am of a different oppinion. B) The more easily grasped models and those with greater practical application get taught first. The more accurate models come only when the student is more able to comprehend them. Only a rare few persons can grasp the esoteric stuff at the beginning. To quote Mr. Miyagi, "first, learn how to walk." Overwhelming a student is not often a good thing.
     
  3. ouabache

    Member

    Jul 12, 2005
    11
    0
    Many of us learned way back in high school chemistry that negatively charged electrons are the mobile charged particles in an atom. After all, when you excite an atom, the electron can jump to a higher orbital or if really excited, exit the outer shell completely. Then in physics we were presented with a similar concept of electron orbital theory in quantum mechanics.

    Only upon learning EE theory, did this concept of moving holes arise. Perhaps every EE student was taken aback (as I was) by this strange concept that seems to fly in the face of everything learned up to that point. Humoring the instructor, the EE student tolerates and eventually learns to accept, that at least in electronic circuits, we can describe positively charged holes as moving. As we now know, since it became a standard convention, that is how we describe current moving in a circuit.
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    The hole flow concept is pretty outrageous at first. We evolved a theory of wire creep to alternatively explain mobile positive donors.
     
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