Where do all the electrons come from?

Factual Questions
21

Not at all. Two points:

First, in undergrad physics, the typical wrong beliefs of incoming freshmen present a known problem, and one typical belief is in the existence of an energy/stuff/substance called “current electricity.” Nope. No such thing.

If you hear students discussing “flow of current,” they need their misconceptions repaired. Charge is what flows in wires, not “current electricity.” In the same way, if undergrad chemistry students truly believe that atoms are like little solar systems, that’s a major misconception, and needs direct treatment.

Since a current is a flow of charge, the common expression “flow of current” should be avoided, since literally it means “flow of flow of charge.”
- Modern College Physics: Sears, Wehr, & Zemanski

Currents may appear, and currents may vanish, but currents do not flow. It’s wrong in the same way that it’s wrong to say “motion moves,” or “speed speeds along.”

Second, textbooks and educators really, really need to be extremely pedantic, otherwise they may be creating misconceptions such as “the flow of current electricity.” Since there’s actually a ‘stuff’ which flows inside wires, we should always use its correct name: charge. Charge flows inside wires. When charge flows, a current appears, and when charge stops, the current vanishes. It’s much like a bicycle chain: the chain’s motion may appear or vanish, but the name of the moving substance is “steel,” and not “current.” Or, it’s much like plumbing or rivers where the moving stuff is called “water.”

In electrical physics, many freshmen really have no clue that wires are full of charge all the time, or that batteryies are just charge-pumps.

The OP’s confusion might even be caused by belief that wires are like empty pipes, and that the electrons are “particles of flowing Current” which fly along at the speed of light. That’s exactly the sort of misconception created by teachers who constantly use the phrase “flow of current,” but who never mention charge-flow.

22

Yes! Very cool electrochem concept. It also applies to salt water conductors, electroplating, and charge-flows in dirt and in human bodies. No electrons flow through YOU, when you get zapped. And what happens if you touch a 9V battery to your tongue, and no electrons flow through the piece of meat? Whenever electrons and water solutions are involved, chemistry is happening.

Simple version: salt water is full of mobile Na+ ions and Cl- ions. Use two wires to connect a long hose full of salt water to a 3V power supply. That gives us a “saltwater wire.” The voltage placed across this “wire” will cause a current, Ohm’s law. All the positive sodium in the water starts moving towards the negative wire, and all the negative chloride moves opposite, towards the positive wire. The motion is slow (but faster than the electron flow in the metal connections.) At the spot where the (-) wire touches saltwater, electrons from the metal are joining with Na+ ions, forming sodium metal which plates onto the wire. Where the (+) wire touches the water, electrons are pulled into the wire from Cl- ions, forming dissolved chlorine gas. More complicated: at the same time, the positive wire is corroding, launching Cu+ ions into the water, producing a colored cloud there, and also H2O is breaking up, creating H+ ions and OH- ions on opposite wire surfaces, which end up as dissolved hydrogen at the neg wire, and dissolved oxygen at the pos wire.

So, it’s probably a bad idea to lick a 9V battery. The flavor is corroded tinplate, plus chlorine, plus a bit of sodium hydroxide and hydrochloric acid. That’s why it stays on your tongue until you wipe it off etc.

Odd concept: in electroplating, the copper ions are coming in from the water and forming a solid metal layer, while electrons are pouring in from the metal, and being cancelled out by the positive ions. This means that, as the metal layer builds up, the speed of layer growth is exactly half of the speed of the electric current in the wire. (Or, the electrons are moving twice as fast as the growing surface of the metal!) This assumes the simple case with single positive ions, not Cu+2 etc. So in general, electrons in wires move at roughly the speed of electroplating layer-growth!

In general, at one terminal the pos and neg comes together and vanishes, while at the other terminal the pos and neg are popping into being, from nothing. Pair-creation and pair-destruction. NOT REALLY! Where the pos/neg are cancelling, neutral atoms are left behind, and they wander off, no longer part of the charge-flow of the circuit. And where the pos/neg are appearing, neutral atoms are being torn open, forming positive ions (corrosion products) which flow along, and also forming bare electrons which are sucked into the metal electrode.

23

Not quite true. In copper, there are no flowing holes. But, if we move the DC wire very slowly, and at just the right speed, we can make the electrons stop flowing, while the positive-charged copper moves opposite. :slight_smile: In non-liquid metals, the positive charges only flow if the metal itself flows.

In fact, electrical engineering looks at all the mobile charges in any conductor: electrons of metal, liquid metal positive ions, pos and neg ions in a plasma, pos and neg ions in electrolytes, proton flows in fuel cells proton conductor, electron beams, proton beams in particle accelerators, mu mesons, positrons, anything. Then it reverses any negative charges and their flow (double negative makes positive amps.) Then it adds everything up and calls it “conventional current.”

That way we don’t have to care whether a current is made of positive ions, electrons, bare protons, etc.

Ammeters measure conventional current. Clamp-on ammeters meters directly measure conventional current. They don’t care if they’re clamped around a metal wire full of mobile electrons, or any other type of conductor at all (they don’t know that the charge-flow in a conductor-tube full of battery acid is partly made of those flowing H+ ions called protons.)

Insight: the amperes, the electric current, is not charge-direction, instead it’s the charge TIMES the velocity, where a negative charge going backwards is exactly the same thing as a positive charge going forwards, is exactly the same as a +2 charge going forwards half as fast. So, pretending that electric currents are electron-flow, that’s not facing reality, instead that’s sweeping all the non-electron currents under the carpet, and leads to craziness such as pretending that there’s always zero current in the electrolyte between battery plates. No, a battery is a conductor, and the path of “flowing stuff” is in, through, and back out again, just like any pump.

24

I guess bbeaty is Bill Beaty IRL. :cool: I just sent you a message about the links on the quoted page above.