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Who first assigned negative to electrons and positive to protons?

  1. Apr 28, 2012 #1

    rbj

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    Who first assigned "negative" to electrons and "positive" to protons?

    a sorta history question...

    the fact that the actual flow of charge (which are electrons in metal conductors) is in the opposite direction of the "positive" current flow in circuits has always been an annoyance to me. the fact that it's electrons that are moving in a conductor is a matter of physical reality, not convention. the fact that electrons and protons both have the same magnitude of charge, but opposite polarities, is a matter of physics, not convention.

    but the fact that electrons were assigned "negative" which necessarily make protons "positive" must be a matter of convention. where and with who did that convention begin?
     
  2. jcsd
  3. Apr 28, 2012 #2
    Re: Who first assigned "negative" to electrons and "positive" to protons?

    I think that you have to accepth that at some stage (I don't know when) it was decided that electric current would be the direction in which + charges flow. This was long before electrons were discovered or atomic structure was known.
    Experiments with magnets and current carrying conductors gave rise to faradays law and lenzs law.... all based on current being the flow of + charges.
    When electrons (cathode rays) were discovered it was found that the deflection of beams in magnetic fields showed that the beams consisted of - charges....there is probably more to it than this but I think the rest is history.
     
  4. Apr 28, 2012 #3
    Re: Who first assigned "negative" to electrons and "positive" to protons?

    Having worked in electronics, I've been bugged by these kind of thoughts for a while too. I assume electrons are assigned as negative in relation to their transitional media as they always seek a ground state, (like when you pick a rock up from the ground, it gains kinetic potential) and thus as electrons move away from an area of charge density the measured action is of a subtractive (or negative) nature. Why this makes anything else de facto positive I'll never know..(though I live in hope:)
     
    Last edited: Apr 28, 2012
  5. Apr 28, 2012 #4

    jtbell

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    Re: Who first assigned "negative" to electrons and "positive" to protons?

    The original "negative" versus "positive" convention, applied to various combinations of objects rubbed together to produce what we now call "static electricity", is due to Benjamin Franklin, around 1750.

    https://www.physicsforums.com/showthread.php?p=2405625#post2405625

    Eventually, it turned out that the objects that Franklin (and others who followed him) called "negative" have an excess of electrons.
     
  6. Apr 28, 2012 #5
  7. Apr 29, 2012 #6

    rbj

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    Re: Who first assigned "negative" to electrons and "positive" to protons?

    of course. that is the convention. water flow is in the + direction of which the water actually flows. only begs the question.

    still only begs the question. so far we are in convention-land. "+" direction is the "normal" direction. big deel.

    who said they were - charges? (it appears, from jtbell, to be $100 Ben.) they could have just as well called those "+ charges" if they hadn't already been assigned a polarity.


    but they could have stacked the Volta pile the other way (upside down from the picture with the Zinc disc on top and the Copper disc on the bottom. if you're saying that the "+" terminal got assigned to the plate on the top (and "-" for the plate on the bottom), which plate is top and which is bottom is an arbitrary decision.

    too bad Benny didn't realize that his "negative" actually had a surplus of the charged particles that actually move around and his "positive" had the deficit.
     
  8. Jan 5, 2014 #7
    Who first assigned "negative" to electrons and "positive" to protons?

    I think you are correct in calling this "kind of a history question," and the first response does fill in some of that history. I also understand that the arbitrary nature of the statement
    makes it unsatisfying as an answer to your question. It seems to me that the conventional assignment
    follows from the equally arbitrary convention of considering "positive" as "additive", "increasing"--"something" rather than "not something".
    So basically, the way I see it, it is meaningless whether flow direction or the electron or anything for that matter is called "positive" or is called "negative".
    Hope this answers your question, OP. :p
     
    Last edited: Jan 5, 2014
  9. Jan 6, 2014 #8

    sophiecentaur

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    You should have a completely neutral attitude to this. The sign of the charge carriers makes absolutely no difference to anything. If you can accept that travelling in reverse can be treated as a negative velocity then the 'electron thing' should be of not more significance than that. Playing devil's advocate, I would say that it is almost a blessing that the electronic charge was found to be negative because it makes people thing twice before making wrong assumptions about the nature of electricity and it should stop you over-simplifying the whole thing. Electricity is not simple and there are no short cuts. The 'Equations' are the closest thing to a valid short cut as they allow you to make very accurate predictions using a very formal model.

    I have had so many kids say to me "they got it wrong about the direction of electric current". They did not get it wrong.
     
  10. Jan 6, 2014 #9

    sophiecentaur

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    Did you ever see a pint of Guinness (Stout) just after it's been poured? You can see, all at the same time, a load of bubbles moving upwards and a load of lovely dark liquid flowing downwards. Which way is 'it' going? The up and the down are all part of the Guinness. There's a nice opportunity for some philosophical thinking just before you pick up the glass and take a drink.
     
  11. Jan 7, 2014 #10

    HallsofIvy

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    I believe it was Benjamin Franklin who first assigned direction to electric current- and got it wrong!

     
  12. Jan 7, 2014 #11

    sophiecentaur

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    Got what wrong?
    If electrons were the only way a current could flow then I might have some sympathy with that view but are they?
     
  13. Jan 7, 2014 #12
    Personally, if I were making the convention, I would have made electrons positive, but as an electrical engineering student, I can tell you that the advantage really isn't as big as you might think. How often do you actually have to imagine electrons moving when solving a circuit? As you get more experienced with circuits, that answer will probably tend towards "never." And anyway, in most of the cases where you imagine charges flowing, it realy doesn't make a difference whether you imagine those charges to be positive or negative. Circuit theory, for the most part, doesn't care whether you imagine electrons moving one way or some imaginary positive particle moving the other way.

    The only case where I've had to spend a lot of time imagining the flow of electrons specifically (not just arbitrary charged particles) was with semiconductor devices. But in that case you have both positive and negative charges flowing anyway (electrons and holes) so it wouldn't really help if electrons were positive. You'd still have to deal with the flow of negative charges.

    I don't think there are very many cases (aside from teaching beginner students about circuits) where making electrons positive would make things noticeably easier.
     
  14. Jan 7, 2014 #13

    DrDu

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    You should also take in mind that not only electrons carry current. Inside every battery, the current is mainly carried by light cations like hydrogen or lithium cations.
     
  15. Jan 7, 2014 #14
    I find this to be an odd discussion. The assignment of a sign to the current was made long before there were any direct observations of the actual charge carriers (as was noted in an earlier post). As far as the scientists at the time were concerned, electricity was the flow of some kind of fluid that they could not directly see. Taking that view, they could equally well analyze it as the flow of positive charges from + to - or the flow of negative charges from - to +. (And of course, they could have reversed the assignment of signs of the voltages as well - it was all arbitrary.) I guess they had a 50/50 chance of guessing whether the actual charge carriers had the charge they called negative or the charge they called positive -and now we know which way it turned out.

    That's still true today for basic electronics - how often do you need to think about the physical charge carriers if you're just designing a basic circuit? We talk about the flow of electrons, but that's really just because we now know about them. We could just as easily talk about positive charge carriers flowing in the opposite direction.

    I'm talking mainly about simply non-transistor circuits, though. I don't know if throwing solid-state devices (or vacuum tubes, for that matter) into the mix requires that we explicitly identify the charge carriers as being negative. (??)
     
  16. Jan 7, 2014 #15

    Integral

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    40yrs ago I was taught electron flow in Navy tech school. They made it clear that positive current flow was being taught in the civilian world. It really does not matter which you follow, positive or negative charges the end result is the same.

    I felt that the Navy's approach was very good, due to that 6 months of education I have had a lifetime of good jobs.
     
  17. Jan 7, 2014 #16

    BruceW

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    in 'conventional current', the current was given the direction of flow of negative particles (i.e. in metals, the flow of electrons). So by conventional current, if there are positive particles flowing from left to right, the current is going right to left. I guess this is fine as a definition. But it is more natural to define current such that it goes in the direction of the motion of positive particles (i.e. not conventional current).
     
  18. Jan 7, 2014 #17
    I think people are mixing up two conventions here. Defining current to be the flow of negative charges (i.e. electron flow vs conventional current) is not the same as defining electrons to be positive and protons to be negative.

    "Conventional current": Electrons are negative, protons are positive and current is the flow of positive charge.
    "Flipped charge": Electrons are positive, protons are negative, and current is defined as the flow of positive charge.
    "Electron flow": Electrons are negative, protons are positive, and current is defined as the flow negative charge.

    In conventional current, current in a resistor always flows from high voltage to low voltage.

    Currents in flipped charge will be the negative of currents in conventional current. Electric fields will also be inverted, and thus voltages in flipped charge will be the negative of voltages in conventional current. Since both current and voltage flip, current in a resistor will still flow from high voltage to low voltage.

    Currents in electron flow are the negative of currents in conventional current. Electric fields and voltages are not inverted, however, so current in a resistor flows from low voltage to high voltage.

    Personally, I think it makes more sense that charges should lose voltage as they flow through a resistor and gain voltage as they flow through a battery, but as long as you label your circuit diagram correctly and stick to one convention, it really doesn't matter...
     
  19. Jan 7, 2014 #18

    BruceW

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    blech, OK I've read a little bit from wikipedia, and "conventional current" is not what I thought it meant. So ignore my last post. Apparently, conventional current simply is the convention that current is positive in the direction of movement of positive charge. (or equivalently, negative in the direction of movement of negative charge). So, there is nothing 'wrong' with this.

    Also, the current that Benjamin Franklin talked about was a one-fluid theory, where the fluid carried a positive charge, and that this fluid flows from silk onto a glass rod when the rod is rubbed with the silk. We now know that it is electrons that leave the rod and flow into the silk. So in this sense, Benjamin Franklin was not totally correct. The fluid (i.e. electrons) have opposite motion to what he imagined.
     
  20. Jan 7, 2014 #19
    I don't think he did. Franklin actually proposed the so called "one-fluid" theory of electricity.
    So he did not assume positive and negative fluids but one electric fluid permeating everything.
    His idea (I think) is that sometime you can create an excess (or deficit) of this fluid on some bodies.
    So the fluid will flow from the zone with excess (plus) to zones with deficit (minus) of electric fluid.
    So plus and minus were not some conventional signs but just "shorts" for more or less (fluid).
    So if we identify the "fluid" with electrons he definitely got it right. It's not his fault that someone put the minus sign on electrons. :)

    Edit. Sorry, I did not see that it was already mentioned in the previous post.
     
  21. Jan 8, 2014 #20

    sophiecentaur

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    There is one massive advantage in the choice of direction for conventional current. It makes everyone stop and think - just a little bit- before they launch into electronics, and make the assumption that they understand much more about electrons than they actually do. If ever a particle was under-appreciated and over-simplified, it is the electron. These forums are littered with glib statements about the nature and behaviour of electrons. The 'direction of current' thing at least helps to isolate electrical theory and calculations away from all that.

    The photon shares some of these problems but at least people seem to acknowledge that most lEM phenomena can be treated using the wave model.
     
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