Why is the charge naming convention wrong?

Question

I recently came to know about the Conventional Current vs. Electron Flow issue.
Doing some search I found that the reason for this is that Benjamin Franklin made a mistake when naming positive and negative charges.
There is even this little comic about that http://xkcd.com/567/

My question is, how can a naming convention be wrong?
Perhaps I don't understand what is the actual mistake here, I don't know. But I don't see how a naming convention could be wrong or right. There is no right and wrong about that. It could've been any other name, like charge A and charge B.

I'll appreciate anyone can help me understand what is wrong in all this.

Answer 1

It's not a mistake, and conventional current is not wrong or backwards.

The labeling of one polarity of charge as "positive" and the other as "negative" is totally arbitrary. It could be done either way and everything would still work out the same. Franklin didn't choose wrong; he just chose. Labeling protons as negative and electrons as positive wouldn't change anything.

Electric current is often defined as a flow of electrons, but this is wrong. Electric current is a flow of electric charge. Charge can be positive (protons) or negative (electrons), and both types of charged particles can and do flow in electric circuits:

• In metal wires, carbon resistors, and vacuum tubes, electric current consists of a flow of electrons.
• In batteries, electrolytic capacitors, and neon lamps, current consists of a flow of ions, either positive or negative or both (flowing in opposite directions)
• In hydrogen fuel cells and water ice, current consists of a flow of protons.
• In semiconductors, the current consists of holes, which are not quite the same as an absence of electrons.

(The Hall Effect can be used to show whether a charge carrier is positively charged and flowing in one direction, or negatively charged and flowing in the other.)

When a Lithium-ion battery discharges into a load, for instance, there is no electron flow in the battery, but there is still a current flow:

(Source: Center for Sustainable Nanotechnology)

If you considered only the electron flow as current, your calculations would be wrong. You need to consider the net flow of charge, no matter what the charge carriers. Conventional current abstracts away the different charge carriers and represents all of these different flows as a net flow of positive charge, simplifying circuit analysis.

Conventional current is not the opposite of electron current, so if they were defined to flow in the same direction, it would be even easier to confuse them and go through life misunderstanding what current is. Electron current is a subset of conventional current. Conventional current combines the effects of electron, ion, proton, and hole flows all into one number.

Wikipedia agrees:

In other media, any stream of charged objects may constitute an electric current. To provide a definition of current that is independent of the type of charge carriers flowing, conventional current is defined to flow in the same direction as positive charges.

Also see Ben Franklin should have said electrons are positive? Wrong.

Answer 2

(Someone resurrected this oldie in the queue, so just to be a contrary voice...)

Ben Franklin did get it wrong. He had just developed a remarkable new theory of electricity in which positive (+) and negative (-) had specific and accurate meanings, and he was unable to apply the two labels in the way he intended.

In Franklin's time electricity was thought to be composed of two fluids, "vitreous" and "resinous", that annihilated each other when they came into contact. Franklin's clever idea was to realize that the two-fluid theory was redundant, and that a single fluid flowing through metals would suffice. This led him directly to an analogy with water pressure or air pressure, in which a single fluid flows from the end of a pipe that has positive (+) pressure, and towards the end with negative (-) or vacuum-like pressure.

The problem was that Franklin had no way to separate the fluid from the metal to tell which way it was moving. He could make sparks, sure, but the fluid (electricity) moved so incredibly fast that nothing accurate could be discerned from watching them.

It was only with the invention decades later of the Crookes tube that it became possible to tell the direction of flow of this mysterious electrical fluid, specifically by watching the shadows it cast on the inside of an empty tube. Only then was it realized that the fluid that Franklin postulated was moving from the "negative" pressure side (-) to the "positive" pressure side, (+). But it was already too late. Decades of papers and textbooks using Franklin's theory and conventions had already been written, and it would have been a nightmare to attempt to flip the convention at that point.

We now call these particles of electrical fluid "electrons," and they do indeed behave very much like the fastest and most nimble fluid imaginable. For the most common way to convey this fluid, via metals, it is the negative terminal of a battery that creates a positive pressure (or voltage) to push the fluid outward, and it is the positive terminal that creates a negative pressure to pull the electrons back in.

(This similarity also explains why using analogies with water pressure to explain voltages and electrical flow can be a lot more insightful than one might expect. Both really are examples of fluids under pressure, even if the terminology is different and the analogy is incomplete due to electrons having the ability to do things that material fluids cannot.)

So, bottom line: Franklin clearly would have labeled his own choice an error if he had had access to better data, so I think we can too.

Answer 3

Central to this discussion is a common and widespread misconception: the wrong idea that electric current is a flow of electrons, and that flows of positive charge are impossible.

Nope and nope.

Only in metals is an electric current a flow of electrons. Protons can flow, and so can ions of both polarities. The type of charge-carrier depends on the type of conductor: metals, electrolytes, ionized gases. So, Franklin may have been "backwards" about way metals conduct a charge flow. But he wasn't wrong about proton conductors and PEMs used in solid-electrolyte fuel cells. Franklin was also wrong about battery acid and neon signs, where the moving charges have opposite polarities and flow in opposite directions. In Franklin's terms, electrolytes contain two (or more) kinds of 'electric fluid,' not just one.

In fact, when you get shocked by a HV power supply, no electrons flow through your body. The voltage impressed across your flesh produces a flow of the ions commonly found in your tissues: positive sodium and potassium ions, and negative chlorides, each polarity of ions flowing in opposite directions. How then can we describe the amperes which are electrocuting you?! Easy. Just use Conventional Current. That's what it's for. (Hint: ammeters measure conventional current. They do not report the percentages of positives and negatives drifting in opposite direction within the circuit.)

It's really quite amazing how many authors seem to believe Franklin's discredited one-fluid theory of electricity, or believe that electric currents are somehow "made out of electrons."

Conductor examples:

Metals - yes, electrons

Semiconductors - electrons in two energy bands (lower band is vacancies or 'holes')

Plasma - electrons, positive ions, negative ions (if Hydrogen plasma, then H+ bare protons are part of the current.)

Distilled water - protons (H+ ions) and OH- ions, no electrons

Battery acid - protons (H+ ions) and SO4- ions, no electrons

Oceans - Na+ ions, Cl- ions, some H+ and OH-, no electrons

Human flesh - Na+ ions, K+ ions, Cl- ions, many misc ions, no electrons

I suspect that WW-2 military training manuals are partly to blame for this situation. For instruction of technicians, their authors concentrated on metal wires and vacuum tubes, and based their concepts on the over-simplified (wrong) idea that "electricity equals electrons," and that all positive charges were really just a case of missing electrons.

Answer 4

This is a common question and the answer is related to the fact that electric current is defined simply as the flow of electric charge. Thus, it is an abstract current since electric charge is a property, not an entity. Electric charge must be "carried" be something.

The direction of flow of positive charge is taken to be the direction of electric current. Thus, a flow of negative charge contributes to an electric current in the opposite direction.

Electron current is the flow of electrons and, since electrons have the property of negative electric charge, an electron current is necessarily a flow of charge, i.e., an electric current (in the opposite direction of the electric current).

But, it is often the case that electric current is due to the flow of other charged entities besides electrons. For example, within the electrolyte of a battery or within a plasma, the flow of charged ions contribute to the electric current.

Answer 5

Sign conventions aren't "wrong", but they can be misleading.

For example, we could re-define work done in a gravitational field so that escaping earth's gravity well would require negative work. That's an equally valid convention, but we associate positive work with effort, so reversing the convention would hinder our physical intuition for no discernible benefit.

Are there cases where intuition might be misleading? Sure; in orbital mechanics, negative work can make you go faster. But that doesn't mean we should reverse the convention just because some people have the misconception "positive work makes you go faster".

For changes in oxidation state, the existing sign convention on charge is "wrong" in the sense of misleading. When an atom gains electrons, it is said to be "reduced" because its oxidation state has gone down.

This is misleading terminology rooted in a misleading convention. Admittedly, the terminology is not misleading for "reduction" involving loss of a proton, but for most atomic interactions it works against physical intuition. For example, ions generally increase in effective radius when reduced.

Students find this so unintuitive that they try to remember it by silly mnemonics like "OIL RIG" ("oxidation is loss, reduction is gain").

Same thing for current: "CCD" is a mnemonic for "cathode current departs", even though most of the time the charge carriers responsible for the current aren't physically departing from the cathode.

Yet those same students don't need a mnemonic to remember the sign for work done against the earth's gravitational field, nor for work done on charges of the same sign.

Answer 6

This just a convention that arose (I think) in the 19th century before the existance of electrons had been established. There is no special significance to it.

In $p$-type semiconductors it's possible to model the current flow as the motion of positive holes, and these travel from the positive pole to the negative pole. However it's still really electrons that are moving, and you'd struggle to interpret current flow in metals using this model.

Answer 7

Positive charges attract negative charges. The same goes for a positive potential (a negative charge wants it's potential to be as high as possible). So the electron flows from the -pole to the +pole increasing it's potential in the proces.

You could see the positive pole as a positive charge that's trying to attract the electon.

Or to follow the approved answer:''It's because we defined the charge of an electron to be the negative charge that these conventions mix up.'' If we were to switch all of the negative charges to positive ones and the positive to the negative ones, then the current and electron flow would coincide. That's simply a matter of convention.

Answer 8

Electricity is a manifestation due to electronic movement, which are negatively charged.

But quite some time ago when this was not known, franklin proposed to call the deficiency of electrons as positive, and excess of electrons as negative; which is followed now!!! which eventually resulted in electronic charge to be known as negative!!!

Poor electron now has to live with the negative charge it was thrusted upon by Franklin.

As a matter of fact, in electrical terminology, current flows from positive terminal to negative terminal; while physically electrons flows from negative terminal to positive terminal. So, now due to that mistake by Franklin we have to call electric flow as reverse of electron flow!!!

I too wish it was the other way round, life would have been a bit more simpler!!