Electric Flow

  1. I've read in my textbook in the elecromagnetism chapter, when a particle is negative and goes through the magnetic field the velocity is opposite to the current...I dont really understand this, can someone please explain this?
     
  2. jcsd
  3. Direction of current is taken to be the direction in which positive charges move in a wire. We know that positive charges do not flow but the negative ones (electrons) do. These charges move in a direction opposite to the direction in which the positive charges were supposed to move. As an anology, you can imagine this.. if positive charges are spontaneously moving from point A to B, it means that B is at a lower potential (negative) and A is at a higher potential (positive). If a negative charge were kept instead of the positive one, it would move from point B to point A (reverse direction). Since we usually measure magnetic fields and its effects based on 'currents', we must adhere to the conventional definition of current. Since an negative charge is always urged to move in a direction opposite to that of conventional current, we reverse the velocity of electrons when calculating effects on it by magnetic fields.

    Hope I was clear.

    Kartik
     
  4. It will be very helpful if you study the Halls effect, and experiments which determines the charge carriers as electrons
     
  5. Integral

    Integral 7,349
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    I was taught electronics, by the US Navy, with negitive current flow. The direction of current flow is intirely arbitray, it is not clear to me why US achedemia insists on teaching a positive current flow.
     
  6. the best choice of all, in my opinion, would be if everyone could just rename the electron to be positive.

    stupid ben franklin
     
  7. Integral

    Integral 7,349
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    Yep!

    Poor Ben, he had a 50-50 chance and blew it!
     
  8. allow me to quote john baez:

     
  9. When Ben Fraklin first labeled charges as positive and negative, whatever way he went about it, he gave electrons negative charge and protons positive charge. Of course he didn't know about electrons and protons at the time, just the charges caused by an excess and shortage of electrons, which he didn't know about.

    Anyway, having labeled his charges + and - he just then said, ok, charge flows from + to - . Unfortunate as we now know that it is only the electrons that flow any they carry their - charge to + areas. However at the time no one could find any difference at all between + and - charges.

    The reason we still use the idea that current flows from + to - is because transistors are easier to understand, if viewed in this way.
    Amoung other things. Of course if w tried to change it now, half of the world would use the old system and half the new and sooner or later ..... BOOOOMMMM!! Nuclear winter.
     
  10. Integral

    Integral 7,349
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    Got news for you, a good part of the world is already being taught negative current flow and has been for the past 30 or 40 years. Transistors work just fine, in fact everything works fine. It is, in fact simpler and makes more sense to track the actual current carriers.
     
  11. Every book I've ever read said that charge flows from negative to positive, negative being where the excess of electrons is and positive being where the deficit of electrons is.

    Am I hearing people say this is not universally taught this way?
     
  12. Integral

    Integral 7,349
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    Shhh....

    American engineers do not realize that the current carrires are negitive, they learn positive current flow. Why? Cus' they seem to think it makes more sense????

    Don't confuse 'm

    :smile:
     
  13. There's a BIG problem here, and it's not with the folks who think that electric current is positive particles.

    Misconception: during electric currents, it is the electrons that flow.

    Why is this a misconception? Because electric current in electrolytes and in plasmas is NOT NOT NOT a flow of electrons. Stick some wires in salt water and you get positively charged sodium atoms flowing one way, and negatively charged chlorine atoms flowing the other. No bare electrons are allowed in water. Zap yourself on a high-volt battery, and the positives flow one way through your flesh while the negatives simultaneously flow the other way. Which one is the current? Both are. You have to add them together... but first you have to reverse one of them, since positive charges flowing leftwards do the same thing as negative charges flowing right.

    Yes, electric current is flowing electrons... WHEN THAT CURRENT TAKES PLACE IN METALS. But there are lots of other conductors besides metal. There are batteries and sparks and fluorescent tubes and living tissues and electroplating baths and fuel cells and ground currents and aurora/solar-wind.

    There are also specialized conductors where the movable charges are the positive hydrogen ions. In other words, PROTONS. These are used in modern fuel cells, but also appear in the everyday world: solid ice is a poor insulator because it's a proton conductor. Go search google for "proton conductor" and I bet you get many thousands of hits.

    Anyone who mistakenly believes that electric current "is" a flow of electrons will have no trouble with metal wires and vacuum tubes. This whole "negative current misconception" was apparently born during the vacuum-tube era and spread by military handbooks for technicians who only had to handle wires and vacuum tubes. But the people taught from these books will have terrible troubles in trying to figure out how batteries work (for example, many of them falsely believe that there is no current in a battery electrolyte; that batteries form an open circuit.) The same people will also feel very uncomfortable when trying to understand how diodes work (to say nothing of transistors.) Those backwards moving vacancies in the p-doped semiconductors are nearly a violation of their "religion." Just don't tell them about proton conductors. It tends to trigger fundamentalist flamewars.

    To understand batteries, fuel cells, sparks & plasma, p-dope silicon, etc., you have to adopt the physicists' viewpoint. You have to convince yourself that electric current can be a flow of negatives in one direction, *OR* a flow of positives in the other direction, *OR* a flow of negatives and positives in both directions at the same time. It all depends on the type of conductor in which the current appears.

    See:

    WHICH WAY DOES 'ELECTRICITY' REALLY FLOW?
    http://amasci.com/amateur/elecdir.html

    and also:

    BEN FRANKLIN WAS RIGHT AFTER ALL
    http://amasci.com/miscon/eleca.html#frkel


    (((((((((((( * )))))))))))))))
    Bill Beaty http://amasci.com
    Science Hobbyist
    billb@eskimo.com
     
  14. Integral

    Integral 7,349
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    hummm...

    You say
    Then you say

    Doesn't the last kind'a contradict the first?

    Pehaps you should moderate that inital statement.
     
  15. Did you learn electronics in tech school or at the naval academy?

    I'm curious because all the engineers I have ever met learned positive current flow but all the electronic technicians learn electron flow. I think it's a conspiracy to keep the technicians from being able to learn from the engineering books. Sort of a protect yourself from unauthorized competition guild thing. I bet the engineers at the naval academy learn positive current flow too.

    I've never had any trouble 'describing current backwards' when teaching tech's but I have met few tech's who can hang with positive current flow. I know by the screams whenever I would slip back into pos. flow with tech's around!

    Besides, the energy is really in the field surrounding the wires and the drift velocity is superimposed on the random motion of the electrons in a metal. If you are willing to abstract that into a imaginary linear flow of ordered electrons who cares if you change the reference direction too?
     
  16. OK. Electric currents are NOT flows of electrons. They are flows of electrons OR they are flows of electrons and positive ions OR they are flows of just protons OR they are flows of positive and negative ions. It depends on the type of conductor involved.

    People who believe that electric currents "are" flows of electron will get lost if they try to understand the parts of physics and electronics where electric currents are flows of something besides pure electrons.
     
  17. Just musing here...

    If a student was convinced that all electric currents were flows
    of negatively charged particles, what would happen? That
    knowledge is useful. It allows us to visualize how wires
    and resistors and coils and vacuum tubes work.

    But if that student started to study transistors, he or she would
    be stopped dead. The student wouldn't even grasp diodes. They'd
    get to the part about hole flow in p-type conductors and get
    stuck. To understand semiconductor devices, you MUST accept that
    the current in some conductors is a flow of positive particles.
    No messing around! No pretending that holes are "really" just
    electrons moving backwards.

    (Also try working backwards... if you don't understand the
    insides of transistors, and don't even have a good hold of how
    diodes work, could it be that you never really accepted that
    positive charges really are flowing through the p-type
    semiconductor?)


    And the "negative current" religion doesn't only keep students
    from attaining a solid grasp of diodes and transistors. Electric
    currents in electrolytes are also non-negative charge flows.
    If you were taught that electric current "is" electron flow,
    then you'll be blocked from ever really understanding batteries,
    or electroplating, or pulses in human nerves.

    The above stuff I'm saying from experience. I graduated engineering
    school and was working for many years before I started re-teaching
    myself simple electricity from the positive/negative current
    viewpoint. Until I re-learned the simple stuff, I had no idea
    how easy it was to understand batteries, transistors, etc. Also,
    I had no idea how BADLY I understood these things until the fog
    started clearing from my mind. My belief in negative-particle
    electric currents was an immense mental block for me. Yet most
    other people have the same block... and if you live in a world
    where everyone has the same disease as you do, you assume that
    such conditions are just normal life, and have no reason to suspect
    that great improvements could be made.
     
  18. having to publish two books...

    Heh. Just by coincidence I stumbled across these two:


    Introductory Electronic Devices and Circuits: Conventional Flow Version, R. Paynter
    http://www.amazon.com/exec/obidos/tg/detail/-/013061761X/



    Introductory Electronic Devices and Circuits: Electron Flow Version, R. Paynter
    http://www.amazon.com/exec/obidos/tg/detail/-/0130617504/


    Heh. To be consistent, he should publish a third and fourth book, "ion flow version" where all the conductors contain equal numbers of opposite charges which flow in both directions at once... and "plasma current version" where the circuits all contain free electrons flowing fast in one direction, and heavy positive gas ions flowing much slower in the opposite direction.

    And what about the particle beam version, where the electrons in conductors actually do flow at nearly the speed of light, rather than flowing extremely slowly as they do in metal wires.
     
  19. Integral

    Integral 7,349
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    This is utter nonsence. I do not recall a single person "being stuck" on hole flow.
    You really need to learn some moderation. This is really not as difficult as you make it out to be. I was taught in the Navy ET A school and we were made VERY aware that it could be viewed from either way, postitive or negitive. We were also taught that any charged partical could be a current carrier if it was mobile. Why are you so agressive about this stuff?


    Once again you are spouting nonsence. Holes are NOT PARTICLES. No There is not doubt about this, an absence of an electron does NOT constitue a particle.

    Interesting concept. I never heard it but that way, it was presented to us as an absence of an electron, which move the other way.


    Seems to me that you are the only one preaching anything.

    Chill out


    Once again this is pretty much nonsence I do not know of anyone that is taught this stuff as a religion, we were taught principles, most of which stood well for me even thorugh a BS in Physics.

    Any one who is taugth basic priciples has no trouble with such things. I think you are full of it.

    Ahh... an electrical engineer.. That explains a lot. Needless to say I do not have high regrad for many of the EE I have worked with through the years.


    this is a huge assumption on your part.

    This last may be your problem. I have to stop an think about which current carrier is being used but in general it does not bother me to move from one to the other.
     
    Last edited: Jan 7, 2004

  20. I had six months of Army schooling dealing with digital communications and also acquired an associates degree in Electronics from a two year program. During both schools, we were well made aware of both positive and negative current flows. We were taught that electrons were not the only charge carriers. During both my military and civilian training dealing with semi-conductor physics, we learned about both hole and electron flow. We did, however deal with mainly the negative current carriers. I never had any conceptual blocks when it came to semiconductor devices.

    When considering P-type materials, the vacancies in the valence shell of the atoms are certainly positive in potential. However, positive current is not the only thing which exists in P-type materials. The flow of vacancies (if they can really be said to flow) depend on the electrons which move to occupy those vacancies. Of course, the electrons need the vacancies in order to move just as the vacancies need the electrons.

    Certainly you can treat vacancies as positive potentials which move in the opposite direction of the electrons. However, I find it difficult to accept holes as real particles. I never heard of them referred to as backward moving electrons.
     
    Last edited: Jan 7, 2004
  21. I just want to point out that in a semiconductor, whether p or n only electrons can move. The acceptor atoms are providing an absence of an electron but all the positive charges are in the nucleus inside the crystal lattice and are immobile.

    Holes are conceptualized as though they are positive particles carrying charge for two reasons. One is that they have an effective mass in moving though the lattice that is heavier than that of the conduction band electrons (holes have lower mobility than electrons). The second is that there are fewer holes to keep track of then there are electrons in the valence band so it's cleaner to keep track of where there is a missing electron.

    Regarding positive charge vs. electron flow for wires, if you think of it as 2 languages say English and French describing the same thing than you see it's good to be able to speak both depending on who's listening. I was taught electron flow in high school and positive current flow in college (every college I've studied at). It served me very well to know both and the tech's all responded very 'positively' to my speaking 'their' language. If I used electron flow around other engineers they would have laughed me out of the building.
     
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