[HN Gopher] Why does current flow the opposite way from the elec...
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Why does current flow the opposite way from the electrons?
After fighting through a bunch of unhelpful answers, one gets to
the bottom of things: Benjamin Franklin chose a convention that
makes electrons negative, and apparently nobody knows why.
Author : johncarlosbaez
Score : 58 points
Date : 2024-06-21 15:16 UTC (7 hours ago)
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| NegativeLatency wrote:
| It was only relatively recently we figured started to understand
| some sort of model of what the inside of the atom is:
| https://en.wikipedia.org/wiki/Plum_pudding_model
| xdavidliu wrote:
| how is this recent? This was like 1900.
| gavindean90 wrote:
| That's more than a hundred years after Franklin.
| zer00eyz wrote:
| Rome was about 2500 years ago.
|
| The first recorded name, 5000 years.
|
| Oldest human structures 10k years.
|
| Humans, about 130k years.
|
| Our oldest "ancestors" 300-400k.
|
| 3.7 billion years.
|
| For you, not so recent. In the grand scheme of things it was
| a heartbeat ago.
| fhars wrote:
| 50% chance events happen all the time (well, half the time).
| nitwit005 wrote:
| Could be worse. They could have chosen any term implying
| opposite. We could have had left and right handed charges.
|
| Although I suppose we essentially did that when naming the
| quarks.
| robocat wrote:
| The worst part is that up and down are not really opposites.
| Down is up on the other side of the world.
| technothrasher wrote:
| I'm not sure I follow you there. In that sense, "down" means
| toward the center of the gravity well. It is the same
| regardless of which side of the world you're on. If you mean
| that "down" changes direction with reference to a straight
| line, ok. But how does that make "up" not the opposite of it?
| crazygringo wrote:
| Up and down are opposites on the other side of the world
| too...
| manmal wrote:
| Or amino acids. Many have a D (Dextrorotatory = right) or L
| (Levorotatory = left) form, indicating into which direction
| they rotate polarized light.
| CapitalistCartr wrote:
| A big part of this is we measure what's important to us. As an
| electrician, what's important is which wire is full of angry
| pixies. They're technical direction of travel is far less
| important to my job (and my safety). When doing electronics, the
| direction of travel becomes quite important. So there's a
| different point of view.
| Gibbon1 wrote:
| Anytime electrochemistry is involved it's important. But
| regular electronics not very much. I think positive and
| negative mostly trips up people trying to use what they think
| is happening to explain theory. When it's not that useful most
| of the time.
|
| What I could never keep straight is anode and cathode.
| justhadto123094 wrote:
| CAThodes are PAWsitve
| g15jv2dp wrote:
| Cats are more intelligent than donkeys (ane in French).
| Cathode is positive, anode is negative.
| Thrymr wrote:
| A CRT display is a "cathode ray tube", which shoots
| electrons, which are negative.
| ars wrote:
| Actually both wires are full of angry pixies, it's just that
| you have angry pixies in your body that match the ones in one
| of the wires, so you don't notice when you touch one, and
| strongly notice when you touch the other.
|
| On top of that if we did not ground one side of the electrical
| network, you could touch either wire and feel nothing. That's
| called an isolated ground, and is not commonly used except in
| hospitals and some other specialty settings.
|
| (If you wonder, we ground one side because if two different
| people both happened to touch a wire, current would flow
| between them using the each.)
| bmacho wrote:
| > that makes electrons negative, and apparently nobody knows why
|
| When there is a symmetry, there are choices, all the time in
| math, and sometime in physics too.
|
| Also I don't like calling electrons negative, they are not. Maybe
| you can say that their charge is -1, when you model charge with
| the additive structure of real numbers / integers, and you choose
| the protons charge to correspond to 1. Modeling charge with the
| additive structure of real numbers / integers is very reasonable.
| (You could use red and blue numbers, but that's not a widely used
| structure.)
|
| So you shouldn't say "electron is negative". That's weird,
| confusing, misleading, and trolling.
| bmacho wrote:
| _Red and blue integers_ : there is red 1, red 2, ... 0, blue 1,
| blue 2, ... . Addition and subtraction as you expect. There is
| no ordering, also no multiplicative structure. There are 2
| isomorphism into the additive structure of the integers. ( _Red
| and blue reals_ are defined similarly.)
|
| I find this structure to model charge better. If not for else,
| at least it prevents you to ask silly questions about charge.
| hawski wrote:
| So you mean red like warm water and blue like colder? Warm is
| + and cold is -.
| crazygringo wrote:
| > _So you shouldn 't say "electron is negative". That's weird,
| confusing, misleading, and trolling._
|
| Huh? By the convention you describe (and we all share),
| electrons have negative charge, since -1 is negative. When
| speaking in the shared and understood context of charge, you
| shorten that to saying electrons are negative.
|
| Nothing weird, confusing, or misleading, and _certainly_ not
| trolling. I 'm baffled where you get that from.
| LgWoodenBadger wrote:
| He comes from an accounting background where commonly-
| understood terms mean the opposite of what everyone commonly
| understands them to mean.
| bmacho wrote:
| I mean I quoted baez, but I quote it again:
|
| > makes electrons negative
|
| It is not true, and trolling.
| throwway120385 wrote:
| Because he didn't know anything about electrons, and the
| experiment he did involving rubbing amber and glass rods on fur
| and silk cloth only showed that something was transferred between
| the two materials, and that when the material containing the
| substance was brought near to the other material containing the
| other substance, the property conferred by the substances
| appeared to negate. If you read Teaching Introductory Physics the
| author very clearly points out that there is no way of _knowing_
| the direction of the charge. It must instead be _decided_ by
| convention. And Franklin simply chose a convention that we stick
| with.
|
| This is where the need to use mathematical formalism to describe
| physical concepts becomes clear. Numbers and numeric quantities
| aren't a real thing that exists in the world. They exist only in
| our minds. And so does the concept of negation. Calling electrons
| "negative" is simply a tool for us to model how the substance
| behaves when it interacts with an "opposing" substance using
| numbers. We could just as easily have called it "black" or
| "white" charge, except that we then need to adapt arithmetic and
| algebra and calculus and so on to work with the concept of
| "black" or "white" quantities if we are to use them to understand
| the substance of charge.
| akira2501 wrote:
| It really seems like had a rationale:
|
| "We suppose as aforesaid, That Electrical Fire is a common
| Element, of which every one of the three Persons abovementioned
| has his equal Share before any Operation is begun with the
| Tube. A who stands on Wax, and rubs the Tube, collects the
| Electrical Fire from himself into the Glass; and his
| Communication with the common Stock being cut off by the Wax,
| his Body is not again immediately supply'd. B, who stands upon
| Wax likewise, passing his Knuckle along near the Tube, receives
| the Fire which was collected by the Glass from A; and his
| Communication with the common Stock being likewise cutt off, he
| retains the additional Quantity received. to C, standing on the
| Floor, both appear to be electrised; for he having only the
| middle Quantity of Electrical Fire receives a Spark on
| approaching B, who has an over-quantity, but gives one to A,
| who has an under-quantity. If A and B touch each other, the
| Spark between them is stronger, because the Difference between
| them is greater. After such Touch, there is no Spark between
| either of them and C; because the Electrical Fire in all is
| reduced to the original Equality. If they touch while
| Electrising, the Equality is never destroyed, the Fire only
| circulating. Hence have arisen some new Terms among us. We say
| B (and other Bodies alike circumstanced) are electrised
| positively; A negatively: Or rather B is electrised plus and A
| minus. And we daily in our Experiments electrise Bodies plus or
| minus as we think proper. These Terms we may use till your
| Philosophers give us better. To electrise plus or minus, no
| more needs to be known than this; that the Parts of the Tube or
| Sphere, that are rub'd, do, in the Instant of the Friction,
| attract the Electrical Fire, and therefore take it from the
| Thing rubbing: the same Parts immediately, as the Friction upon
| them ceases, are disposed to give the Fire they have received,
| to any Body that has less. Thus you may circulate it, as Mr.
| Watson has shewn; You may also accumulate or subtract it upon,
| or from any Body, as you connect it with the Rubber or with the
| Receiver; the Communication with the common Stock being cut
| off."
|
| from Benjamin Franklin's letter to Peter Collison, May 25,
| 1747.
| throwway120385 wrote:
| But his choice of "positive" or "negative" are entirely a
| convention of how he wanted to think about things. There's
| nothing special about the sign other than it made it easier
| for him to reason about what was happening.
| wycy wrote:
| It's really strange reading the words of such an intelligent
| person beginning to understand something back then that is so
| fundamental today that even laypeople understand it more
| scientifically. Really weird, but really cool to get a peek
| back into a scientific mind in the 1700s.
| jstanley wrote:
| > even laypeople understand it more scientifically
|
| Laypeople use more scientific-sounding words, sure, but
| what more scientific way is there to _understand_ something
| than to have discovered it yourself through experiment?
| detourdog wrote:
| I often prefer the original language of discovery. My
| favorite is the term accumulator compared to battery.
| pdonis wrote:
| _> there is no way of knowing the direction of the charge_
|
| But there is--otherwise we wouldn't know that Franklin got it
| backwards. He thought the charge carriers were going one way,
| and chose the convention he did because he thought it matched
| the way the charge carriers were going, but it turns out they
| were going the other way. The signs of the charges are a
| convention--and the fact that we still use Franklin's
| convention and it works just fine attests to that--but the
| direction the charge carriers move is not.
| Am4TIfIsER0ppos wrote:
| Electrons were not discovered for more than a hundred years after
| his death. How could he have done the "right" thing other than by
| chance?
| imchillyb wrote:
| If one takes into account the field dynamics, the electrons are
| indicators of electromotive force and not the originator. The
| electromagnetic field connects the circuit and then _drags_ the
| electrons with it in a flow.
|
| Technically the opposite flow theory would be the opposite
| reaction to the field drag. Every action has an equal and
| opposite reaction. The equal reaction would be the electrons
| being dragged with the field. The opposite would be the current
| flow we observe.
|
| I can't wait until we can more clearly and accurately view the
| different fields that make up everything we know. It's fields all
| the way down.
| tdeck wrote:
| Everyone is giving correct answers so I'll just add something: in
| some parts of the world the convention has been to consider
| current flowing from negative to positive. For example in
| Scotland it's often taught that way apparently:
| https://www.mrsphysics.co.uk/blog/why-electron-flow-scotland...
|
| I read somewhere that this was also common in the USSR but can't
| find any references. Perhaps someone here will remember.
| sobellian wrote:
| Charge carriers aren't always electrons anyway, so you're
| restricting yourself by thinking of current as electrons moving.
| Even in the usual case where electrons are the charge carrier, it
| is only the small net movement of zillions of electrons back and
| forth which produces a current. So in any case current is a
| macrostate and electron movement is a microstate, and sign
| convention won't change that.
| tedk-42 wrote:
| Exactly this!
|
| Even the use of 'flow' is misleading. It's barely trickling
| through the wire...
| arnarbi wrote:
| Others have answered correctly (it was an arbitrary choice), but
| fwiw I always found it helpful to think of current as the
| direction of the "holes" where electrons can be.
|
| Like bubbles rising in water, the holes "travel" opposite the
| potential that's pulling the surrounding electrons the other way.
| boring-alterego wrote:
| Fun fact when in 2 year school for electronics engineering
| technology we learned the current flow with the electrons, and in
| my 4 year electrical engineering school I learned it by following
| electron holes.
|
| You'll find basic electrical circuits books sometimes have an
| electron flow edition.
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