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Which way does current flow??

Discussion in 'General Electronics Chat' started by Peter_wadley, Jul 5, 2007.

  1. Peter_wadley

    Peter_wadley New Member

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    Hey,

    I know this is a very trivial thing to know BUT.. Im getting really confused!

    First I was told that current flows from the POSTIVE(+) terminal of a battery through a given circuit then to the NEGATIVE (-) terminal..

    I was happy!

    Then in Chemistry we began electrochemical cells.. here I was told current flows from the NEGATIVE to the POSTIVE!

    BTW, When I say current I mean the electron flow direction.. :eek: Just making sure Im not completely doing this assbackwards.

    Then in physics we learned photoelectric tubes.. again electrons travelled from the negative to the postive terminal.. I asked my teacher which way electrons travel since Ive been told time and time again:

    'Electrons travel from postive to negative'

    What is postive and what is negative.. :eek:! Since electrons are negatively charged is the negative full of electrons and the postive electron deficent?

    ARGH!

    Then I began reading about conventional current flow.. !

    :eek:

    Can someone please break this down in a very simple manner..

    In electronic circuits.. Which way do the electrons travel? When an LED ON which way is the current flowing?

    Thank you
     
  2. j.p.bill

    j.p.bill New Member

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    Can't imagine why somone would tell you that electrons go from positive to negative. They carry a negative charge, and so travel from cathode to anode, or negative source to positive.

    Some confusion came from the old days of vacuum tubes. The plates all went to B+, and a positive current flow was the convention. When reminded that electrons are the only charge carrier available in copper wires, things almost got straightened out. Notice that in symbols, the diode arrow points against the current.

    In an electrolyte like salt, you have a dissociation into Na+ and Cl-. Placing a pair of electrodes in the solution will have both charge carriers moving towards the oppositely charged electrode. Wires only carry electrons, though, so current is a flow of negative charges.
     
  3. KevinAlaska

    KevinAlaska New Member

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    Doh! I went back and deleted all the extra posted posts and not realizing it I deleted the second post that started all this trouble for me.. so here I am to post it again...

    okay you mentioned putting the help down in a 'simple maner'

    Well lets use the battery for my example. The positive side is full of atoms that have electrons (- charge) so they are in need of electrons to make them neutral again. the negative side of the battery are full of atoms that have extra electrons, making them negatively charged.

    So the Atoms that are missing electrons (the positive charged) having a strong want to fill those missing electrons in those missing slots. this pull adds to the side of the battery with the negative charge the side with extra electrons. These electrons that are extra are not held very well to the atoms and in a way don't feel very much love so they are easily pulled off of those atoms to the postive side. this difference between the two sides create teh voltage.

    As those electrons find their new home on the postive side those positive atoms became from positive to neutral and there for are happy atoms. also known as stable. this difference becomes smaller and then therefore there is a smaller voltage between the two sides of the battery. This would explain whey if the battery is used in a flash light the light would get dimmer. Less electrons to help to job get done.

    Sincerely,

    Kevin in Alaska
     
  4. dave

    Dave New Member

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  5. Peter_wadley

    Peter_wadley New Member

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    Thanks so much j.p.bill & KevinAlaska!

    Completely cleared up now.

    Take Care
     
  6. Peter_wadley

    Peter_wadley New Member

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    Hmm,

    I kept thinking about this so I had to say it..

    If electrons travel from - to +

    Then why do the arrows of transistor schematics always point from Collect(+) to Emitter(-)

    Likewise, and this was mentioned above, why do diodes point to the negative lead?

    Was someone drunk while designing these pictures?
     
  7. john1

    john1 Active Member

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    Hi,

    I was told that in the early days they reckoned that electricity was
    some sort of flow, but they were not sure what.
    The direction of the supposed flow was thought to be the same as
    electro-plating, where metal transfers from one electrode to another.

    In electro plating the transfer of particles is from the positive to
    the negative electrode.
    The mechanism behind electro plating is now understood, but in the
    early days is was thought that the current carried the particles
    along in some way.

    I was told that this is why they originally thought that electric
    current went from positive to negative.

    Later, when devices came along that illustrated the movement was in
    fact electrons, and they travelled from negative to positive, the
    convention was maintained probably because they thought it would make
    no difference to anyone which way it went, since only a few people
    were knowledgeable about it anyway. That turned out to be a poor
    decision as electrics was a fast growing field and soon many people
    became involved.

    So thats how i was told that we have 'Conventional current' and
    'Electron flow'. The two were taught side by side for many years, and
    for all i know they still are.

    Now we are left with this little contradiction in the arrows of the
    schematics, it is now so entrenched that it is likely to remain for
    good. Once you know about it, then it ceases to have any mystery.

    If anyone else was told any other story about this, then i would be
    interested to read it.

    Regards, John :)
     
  8. Leftyretro

    Leftyretro New Member

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    That was basically how I was taught in US military tech school why their are different electron/'current' flow directions, minus the electroplating explanation. The Conventional current crowd has sense tried to modernize their paradigm, at least for solid state devices, by defining 'hole flow', which is said to flow opposite the electron flow, thus allowing them to maintain their silly arrow symbols.. ;)

    Seems to me pretty simple, electrons are the only physical thing flowing and that's from - to +, end of story.

    Lefty
     
  9. miyagi

    miyagi New Member

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    Only the electrons flow from one point to another, from an area of more electrons (negative charge) to an area lacking electrons.
    The conventional way which was according to Benjamin Franklin (current flows from positiVe to negative) is the hole current flow in which the movement is the opposite of the electrons. The arrow in the diode's symbol is the direction of the hole current flow which is the reverse of the electron flow.
     
  10. Tomble

    Tomble New Member

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    "Current" is not normally "electron current"

    Hi Peter,
    It seems to me you've got your wires crossed (no pun intended) and nobody much is exactly setting you completely straight on this. :(

    It looks like you're repeatedly supposing that when people say "current", at least in terms of its direction, they mean "flow of electrons". This is NOT the case. When people talk about the direction of current, assume they ALWAYS mean "conventional current" unless they say otherwise. Conventional current is the flow of "positive charge", and goes from the POSITIVE supply terminal to the NEGATIVE. It doesn't *MATTER* that (outside of electrolytes) there aren't really any mobile positive charges. That is what the convention is. 99% of the time you can forget all about the electrons. :) If it helps, you can imagine there are really little positive charges flowing through the wires instead, the circuits won't mind as long as you don't tell anyone. ;)

    They didn't make this up to confuse you, or be bloody-minded. "Charge" has been known about for CENTURIES- capacitors for instance have their origins in the 18th-century *Leyden Jar*, and people have known about *static* electricity since Classical times :-O. After some point, experimenters figured out that there were two different types of "charge", whatever they were, that different methods of generating static produced one type or the other, and that the "charges" behaved in certain ways (opposite charges attract, and cancel each other out if they meet, and like charges repel each other). Now, maybe picture a conversation something like this:

    A-Hello there B, what you got there?
    B-Some "charges"! I've stored them in the jars using my electrophorus- as you can see, the electroscopes are showing their presence.
    A-Oh yes, so they are! I guess. How come you've got two different jars?
    B-Oh, you can't store different kinds in the same jar, they cancel each other out. One "subtracts" from the other, essentially.
    A-There's different kinds? Oh. How do you remember which is which? I can't see anything apart from those "electroscopes" which look much the same to me.
    B-Eh, well I've been thinking of naming them. I'm going to call the one that I get from rubbing silk on glass rods "positive", because it's a really positive experience, and uh, well the other type "subtracts" from the positive charge, so I'll call that "negative".
    A-Rubbing silk on glass rods is a positive experience?
    B-Not really, I made that up. But that's what I'm going to call them, anyway. And as current is the flow of charge, we shall say that it's specifically the flow of *positive* charge. That's a bit arbitary too, but we know that the direction of current makes a difference, so we might as well decide which charge's movement we're calling the current's "direction" so we can talk about it.
    A-Hmm. Hey, shouldn't you wait for JJ Thompson to discover the electron?
    B-HUH? NO! Go away. Fleming needs us to make a decision so he can tell what way round to point his fingers, and I'm not even sure if Thompson's been BORN yet.
    A-Good point. What year IS this anyway? And who are we?
    B-Sorry, I forget. I'm only allegorical anyway, or something.​

    May have been Benjamin Franklin, I'm not sure and it doesn't matter :D. The electron has only been known about for slightly over 100 years now, and they'd already been doing a LOT of mucking about with electricity by then, the conventions have stuck and there is no real reason to change them other than to cause a lot of disruption.

    As for the "charge carriers" part, note that in some media (p-type doped semiconductors), the current is strictly carried by POSITIVE-charged "holes" (the lack of electrons prevents the POSITIVE charges of the nuclei being cancelled out), and as j.p.bill there pointed out, current in electrolytes is carried by BOTH polarities of charge (ions, which genuinely exist in both types). So if you choose to interpret "current" as "direction that the charge carriers go in", then you have the situation where your version of "current" completely reverses direction repeatedly through most circuits, and through any electrolyte it is either "going both ways at once", or else you can consider it to have NO net flow! This is clearly *nonsense*. Current goes in one direction around a circuit, and components in series have the same current through them. The "flow of a specific polarity of charge" definition works that way where the "flow of charge carriers" one doesn't.

    So I'll say again. Ignore what the "charge carriers" *REALLY* are, it makes no difference AFAIK outside of the realms of Hall-Effect devices (which you don't usually have to make yourself, even if you need one!!), and you should generally not need to care whether you have positive charges going one way, or negative charges going the other way, because for the majority of purposes it amounts to the same thing :D. Hence yes, electron flow is from - to +, because electrons are negatively charged, and "current" is from + to -, because "current" refers to flow of POSITIVE charge.

    As for the strange electrochemistry example, it could be that your teachers were describing the electron flow inside the (battery) cell, where the situation is reversed. Remember the current flows in a CIRCLE in a circuit (ignoring parallel bits etc), that is where the name "circuit" comes from. The EMF of the cell is generated by the chemical reaction inside pulling electrons from the positive terminal and dumping them on the negative terminal, which is what makes them "positive" and "negative" in the first place. (It does this by positive ions going one way and negative ions going the other- again, TWO charge carriers in an electrolyte!)

    Or it could simply be they were referring to conventional current outside the cell, and you got confused because you were thinking of "current" as meaning "flow of electrons". It's understandable you should be confused if nobody cleared that mistake up properly. :(

    Well anyway, that was a lot longer than I'd have liked, but I hope it helped you or some random passer-by anyway! :)
     
  11. Bob Scott

    Bob Scott New Member

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    Simply stated, when Ampere had to guess which way current flowed, he had a 50-50 chance of getting it right. He guessed wrong, but the convention has become standard.

    Bob
     
  12. miyagi

    miyagi New Member

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    But i thinks it is right to say that the current flows from negative terminal to positive terminal, and not the conventional way! Current is the amount or the number of electrons passing or moving along a conductor. Some just give reasons to accept the conventional way of current flow. :(
     
  13. Peter_wadley

    Peter_wadley New Member

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    I agree with you miyagi.

    The argument seems to be that since current can be either Negatively or Positively charged.. then surely the postive 'holes' should be considered current..

    Current as defined in the dictionary:
    Electric current is the flow (movement) of electric charge


    MOVEMENT! Only electrons can move!! (significantly) Therefore why would any one even consider the positive charges as current if they cannot move!

    Electronics is the guiding of ELECTRONS inorder to make something happen.

    Therefore in my personal opinion, Electrons are the only charge I care about.

    However, Im sure my attitude would change if I were to get into nanotechnology or semiconductor design/engineering.
     
  14. Hero999

    Hero999 Banned

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    Who cares?

    Conventional flowis fine for understanding most circuits so it doesn't matter.
     
  15. KevinAlaska

    KevinAlaska New Member

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    I remember being told versions of the following and from the physics I have had in the pass it sounds correct...

    If atom A, B, C are in a row side by side then...(considering these are all a conductive type atom)

    If atom A gets it outer orbit electron (in almost all cases outermost ring) pushed (by a voltage) then it move on and comes to atom B. The new electron jumps onto the orbit of atom B and then pushes an electron off the orbit it now is on off the atom B. Atom B's new lost electron goes to atom C and pushes off an electron as it takes hold on atom C from atom B... so on and so on.
    Like pushing marbles through a straw that is big enough to hold them. any new marble pushed in pushes out another marble at the end of the straw.

    oh well... :)

    Sincerely,

    Kevin in Alaska
     
  16. Hero999

    Hero999 Banned

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    The only time you should care is when you're talking about electrolysis or how semiconductors themselves work.

    No one cares if all they're doing is figuring out how an astable 555 timer works.
     
  17. Peter_wadley

    Peter_wadley New Member

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    Well, its one thing to DO.. and its one thing to KNOW.

    If no one 'cared' in the first place there wont even be a 555 chip
     
  18. lucky1

    lucky1 New Member

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    just look at a schematic and find a diode and remember that current flows the way the horn blows. Voltage is + to - and current is - to +.
     
  19. Peter_wadley

    Peter_wadley New Member

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    How so? 10 CHARACTERS!
     
  20. Tomble

    Tomble New Member

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    Sheesh :(

    Look, Hero999's point is what I'd been trying to get across, basically (and I'm glad someone more authoritative than just some newbie like me says it). When they figured out that actually electrons existed, and the parts that really moved (in most situations) were only negative charges, they did at least have enough sense to know that:
    -Continuing to refer to current as the flow of positive charge would not have caused them any problems in their calculations, except maybe in VERY esoteric cases, where the few people who really needed to know would be able to COPE with the fact that their standard terminology was not a strict reflection of reality. The effect is EXACTLY THE SAME normally.
    -Whereas suddenly deciding "Actually from now on, we're going to say that 'current' is the exact opposite to what we've been saying for decades, and we're going to change all of our rules that refer to 'direction of current' to go the other way round" would actually cause chaos.

    This hasn't AFAIK changed at all, even with the advent of semiconductors.
    I suspect even this is arguable, frankly, though I won't be the one to do it (but I will throw out there the reminder that some of the earliest transistors were bits of rock with wires stuck to them).

    Seriously. You do not need to care whether the current is actually carried by electrons. Can you see them? NO, so they're hardly "in-your-face". Will they go on strike if you don't give them enough credit? NO. Does it make any difference to the behaviour of your circuits whether the current is really carried by electrons, holes, positrons, protons, fairy dust or marmalade? NO, unless you're doing something particularly unusual, in which case you can set aside the convention for a few minutes just for that part before continuing. Does it make any difference if you use terminology that is completely opposite to the rest of the world? YES, quite a lot. For you, for me, for strange Victorian people, for everyone. Hence the term "current" IS the flow of positive charge, and goes from + to - regardless of fine details of what is actually going on, not so people can be weird traditionalists who live in some ivory tower, but so everyone can understand WTF everyone else is talking about. It's called "pragmatism", or "practicality". Some people find it beneficial.

    Ok, regardless if this argument continues, I'm not getting dragged in any further, everyone else can suit themselves one way or the other :p
     
  21. Peter_wadley

    Peter_wadley New Member

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    Well I’m glad God has now spoken. We can blindly follow you and your theories now.

    Your post, Tomble, seems to be written much like the bible. Full of arguments stated as fact, yet with absolutely zero information to back it up.

    Its basic human nature to want to know everything about 'our' universe. This is no exception.

    Lets review your reasons 'why' we shouldn’t care about electrons

    So if you don’t see something it is unimportant to us?

    Hmm

    Air: Can't see it. Can't live without it. Need I say more?

    IR Light: Can't see it. I guess we will need to get off our asses now and tune the TV.

    Photons: I guess this goes with IR.

    Waves: I’m glad theorists like Young, Franklin, Einstein and Newton didn’t have your 'If you cant see them, they aren’t important!' attitude. Trying to name all of the technologies derived from this knowledge would be like trying to write down every lottery permutation.

    Forces: Just because Newton couldnt see what was pulling that apple down, did he rule it as unimportant? Thankfully no, he didn’t.

    The force of Gravity is not "in-your-face" yet if you were to jump off a building.. well I'll let you decide once you hit the ground.

    God(s): Billions of People are devoted to one. Believers view God as VERY important. Has any every appeared? (sorry for even mentioning this one)

    Point is, just because our eyes cannot see something does not make it uninfluential to reality.

    Not going to touch that one.

    Give me a break. Would not all transistors and diodes change polarities?

    Magnetic fields around a current carrying conductor would change directions.

    Im sure after university I will be able to list alot more.

    So its the flow of electron deficient areas per unit time?

    I guess I could go for that.
     
    Last edited: Jul 10, 2007

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