Sciencemadness Discussion Board

What is electricity?

vmelkon - 16-10-2016 at 10:58

Hello people,
There is a thread over at
https://www.youtube.com/watch?v=7NCs7YiFRBU

The conversation is about electricity and how 18th century people got the direction of flow wrong. What is electricity? Lee Merkin says that it is arbitrary:

===============COPY OF THE CONVERSATION:
Lee Merkin:
Because it's not really a mistake. It's arbitrary. The conventional current flow is in the opposite direction to the electron drift, but of course in devices where holes are the majority carriers (of which there are many) current flow is in the same direction as carrier flow. So long as in any system model there is consistency applied to each vector, the answer is the same.
===============
Me:
It is a mistake. The electrons are the ones that move. Holes don't flow. That is a model in semiconductor physics. Now if we were on a planet with antimatter, then the direction would be correct. Positrons would be the ones flowing.
===============
Lee Merkin:
Holes absolutely DO flow in many, many electronic devices where holes are the majority carriers.

...also, electrons themselves are models in semiconductor physics just as holes are. They aren't little particles whizzing through wires. Instead they are a probability distribution of orbitals around the nucleus of the atoms in the conductor or semiconductor, the distribution of which forms the valence and conduction bands in the material. Applied voltage causes atom to atom energy transfer for through electron-electron and electron-phonon (loss) interaction giving rise to the phenomenon of current flow and resistance. It so happens that the electrons drift in the opposite direction the the arbitrary conventional current flow, but then holes drift with it. So perhaps you can see that the simple model you are referring to is actually not wrong, it is oversimplified.
===============
Me:
It has been established that electrons are the charge carriers. They are the ones that flow. Whether you think of them as particles or a wave distribution doesn't matter. The best way to determine this is through a vacuum tube and to show which side a shadow is cast. 18th century people got it wrong.
===============
Lee Merkin:

You are demonstrably incorrect. ELECTRONS DO NOT FLOW. Charge flows, and the electrons themselves remain pretty much stationary in comparison.

Now stop thinking you know everything and realize that some of us have qualifications and jobs in this field!

DraconicAcid - 16-10-2016 at 11:58

Weird. You can visualize it as holes flowing or electrons flowing, but to say that one flows more than the other is utterly wrong.

I can see what he means by electrons staying pretty much stationary, but it's still their flow that causes electricity.

elementcollector1 - 16-10-2016 at 12:02

I think you need to stop being so salty about electron-hole theory. It's a good model, and it's worked for a variety of engineering applications.

Also, you're committing a bit of argumentum ad verecundiam at the end there.

Dwarvensilver - 16-10-2016 at 13:48

I don't know, I am kind of leaning toward vmelkon's idea. I know as well that one electron does not travel through the circuit from start to finish.
Electrons are indeed charge carriers of the negative charge, but the electron has to move from its original atom to the next to cause the charge to flow as in:

"Using enough electrostatic force on the valence electron–either pushing it with another negative charge or attracting it with a positive charge–we can eject the electron from orbit around the atom creating a free electron.

Now consider a copper wire: matter filled with countless copper atoms. As our free electron is floating in a space between atoms, it’s pulled and prodded by surrounding charges in that space. In this chaos the free electron eventually finds a new atom to latch on to; in doing so, the negative charge of that electron ejects another valence electron from the atom. Now a new electron is drifting through free space looking to do the same thing. This chain effect can continue on and on to create a flow of electrons called electric current."
Excerpted from https://learn.sparkfun.com/tutorials/what-is-electricity/flo... One of many sites that say the same thing. Lee Merkin's description sounds like charge is another entity.

[Edited on 16-10-2016 by Dwarvensilver]

aga - 16-10-2016 at 14:14

It does not matter whether anything can be identified as Moving or not.

Electron, Lack of electron, Alien nanobot, carbon dream etc.

The Energy transfers over Time and Distance.

That is what makes things happen: the movement of Energy (over time).

The Physics are complicated, not 100% understood, and i won't tell anyone how it all actually works until Total World Domination in the arena of Interpretive Dance is achieved.

Next Weekend may be a bit of an optimistic estimate, granted.

(skips lightly sideways, crosses feet to make a precise X, raises one arm at exactly 30 degrees, then falls to the floor exactly as a tree would if felled by a stream of supersonic marshmallows)


[Edited on 16-10-2016 by aga]

phlogiston - 16-10-2016 at 14:57

Consider current in an electrolytic cell.
It is not carried by free electrons, but by cationic and anionic species.
Consider muons moving through an accelerator tube. That is also an electric current, measured in amperes.

I would go with Lee Merkin. Charge flows. That fundamentally defines an electric current.

vmelkon - 16-10-2016 at 18:22

Quote: Originally posted by phlogiston  
Consider current in an electrolytic cell.
It is not carried by free electrons, but by cationic and anionic species.
Consider muons moving through an accelerator tube. That is also an electric current, measured in amperes.

I would go with Lee Merkin. Charge flows. That fundamentally defines an electric current.


I am confused. Lee Merkin says that ELECTRONS DO NOT FLOW and that charge flows.
In your example, the cationic and anionic species flow.
In an accelerator tube, muons are flowing.

What is flowing in a piece of zinc when you connect it to a power supply?

phlogiston - 17-10-2016 at 01:32

Yes, ok that statement "electrons do not flow" is false.
Ofcourse, in metals, electrons do flow and I don't agree with that aspect of his definition.

But the part that a more fundamental definition of electric current is that is consists of moving charges seems correct to me.

In the case of a piece of zinc, electrons carry the charge. You can put a few electrons into one end of the zinc and you get a few electrons out from the other end.

j_sum1 - 17-10-2016 at 03:25

If I electrostatically charge some ping pong balls with a positive charge and fire them from a canon then I have flowing charges -- electricity. The nature of the charge carrier does not matter at all.

Also worth noting that in the case of electrical current through a wire, the average electron drift may be in the order of metres per hour. Or indeed zero in the case of AC. Whereas the charge flow and the rate at which an electrical field is set up is nearly instantaneous - close to the speed of light. By comparison the drift rate of carriers is almost nothing. **


** A proton beam in a particle accelerator does have a high velocity for the carrier. But that is not a particularly common application.

vmelkon - 17-10-2016 at 10:51

Quote: Originally posted by j_sum1  
Whereas the charge flow and the rate at which an electrical field is set up is nearly instantaneous


I guess I am confused by "charge flow".

Yes, the electric field that sets up in the zinc wire would be at light speed. What the heck is the charge flow? Are you talking about electrons?

j_sum1 - 17-10-2016 at 12:18

The rate at which the electric field propagares is near light speed.


Tthink of water in a hose. Water comes out the nozzle a split swcond after turnibbg the tap on. But indicidual water molecules take a lot longer to travel the length of the hose.

aga - 17-10-2016 at 12:45

Maybe think of a wave moving across the sea.

The water is only going up and down, but the Wave moves across the surface, and exerts a force when it hits the beach.

Maroboduus - 17-10-2016 at 18:37

It's actually smoke travelling inside the wires.

That's why when you get a short or a burned condenser in an electronic device it fails. Because the smoke got out.

This theory matches my empirical observations quite well, and I'm sticking to it.



phlogiston - 18-10-2016 at 05:18

The analogy with water can work quite well, even for relatively complex electronic phenomena.

It works best if you consider voltage to the analog of water pressure and current analogous to water flow, and picture AC current/pulses of voltage as longitudinal pressure waves, not as transverse (waves on the surface)

A tube filled with water is the the equivalent of a conductive wire of metal.

Imagine you press a bit of water into the tube at one end. What will happen is that the pressure suddenly rises at that end of the tube, and that pressure is quickly transmitted through the water in the tube to the other end, pushing a bit of water out of the tube (if it is open) or raising the pressure of the entire tube (if it is closed on the other end).

The electrical equivalent is: you connect one end of the wire to the negative pole of a battery. If the wire is not connected to anything else (the close water tube), the potential (pressure) of the wire changes to become equal to that of the connected pole of the battery. If the wire is connected across the two poles of the battery (open tube), a current flows (water/electrons go in at one end, the same amount of water/electrons are pushed out at the other end).

[Edited on 18-10-2016 by phlogiston]