What is electricity exactly?

Bassalisk

Quote by sophiecentaur

Current is the Time derivative of Charge. NOT the speed of charge carriers. Do you not see the difference? This is so basic.

Ok i rest my case.

sophiecentaur

Which one?

Bassalisk

Everything.

sophiecentaur

Quote by Bassalisk

Everything.

Meaning that the "propagation of current" (whatever that means) is very fast? But we know the charge carriers in a metal move verrry slowly but in a CRT they go very fast. Perhaps you mean the Energy is transferred very fast. Yes - quite near the speed of light.
You could, at least, try to use the right terms if you want to change the course of Physics.

Bassalisk

Well yes, when u put it that way.

toneboy1

This was a great thread.

sophiecentaur

Quote by Bassalisk

Well yes, when u put it that way.

DragonPetter

Quote by Bassalisk

I strongly disagree with definition that current is MOVEMENT of electric charge. This is wrong, in my opinion, on some very important levels. Current is, for me impulse of energy. It is in some cases movement of charge, but in general theory where circuit is analysed, its not.

If that is definition, that means that charges in the wires move at speeds near speed of light, which we all know don't. They move very slow at drift velocity. Further this would mean that the wire would get super hot in very short time.
Current is a wave, similar to electromagnetic wave that propagates through medium.

Current can be defined as actual charge carrier flow. I think the mix up is thinking of flow rate as speed (displacement rate) - they are not the same thing. Is it safe to say current flow is more similar to a flux concept than a displacement concept? If you look at a certain cross section, current is the number of charge passing through that surface at a given time. You can have a lot of charge move really slowly (and so displace very little distance), and it will still be a high current because the number of charges is so high.

sophiecentaur

Just consider a CRT circuit. The same number of electrons per second going all the way round. The ones in the wires going at snail's pace and the ones in the tube going at a speed not much lower than c. Flux not speed.

Kholdstare

Its flow of electric charge.

sophiecentaur

Quote by Kholdstare

Its flow of electric charge.

Nothing wrong with that but the term flux gets further away from the implication of speed which we need to avoid, perhaps.

toneboy1

Quote by sophiecentaur

Nothing wrong with that but the term flux gets further away from the implication of speed which we need to avoid, perhaps.

h'mm, ok that confuses me a bit, we agreed that I = time derivative of charge = charge/time
(I think)

So as the electrons are drifting IN THE WIRE quite slowly SOMETHING is moving near the 'speed' c depending on material. But we also said that current = flow of electric charge ??

*EDIT*
could we model the flow of charge like a sound wave, electrons pushing on each other but not really moving position?

sophiecentaur

Better. Whatever the 'amount' of current, the signal / energy / wave gets there at the same speed.

Kholdstare

Quote by sophiecentaur

Nothing wrong with that but the term flux gets further away from the implication of speed which we need to avoid, perhaps.

Well, basically flow of charge is what defines current. However, one can draw a relationship between drift velocity and current. I = q x n x A x vd. But saying that the current is all about speed and nothing else is false. The (average) speed of electron multiplied by electron concentration per unit length (nA) gives the number of electron passing a particular point (actually area) of the conductor per unit time.

toneboy1

Quote by Kholdstare

Well, basically flow of charge is what defines current. However, one can draw a relationship between drift velocity and current. I = q x n x A x vd. But saying that the current is all about speed and nothing else is false. The (average) speed of electron multiplied by electron concentration per unit length (nA) gives the number of electron passing a particular point (actually area) of the conductor per unit time.

That seems completely different to:

Quote by sophiecentaur

Current is the Time derivative of Charge. NOT the speed of charge carriers. Do you not see the difference? This is so basic.

I'm sure Bassalisk would have a fit...

DragonPetter

Quote by toneboy1

That seems completely different to:

I'm sure Bassalisk would have a fit...

They are not different, only different levels of describing the same concept. Kholdstare is explaining the physical description of how it comes about which shows that you can derive the flux (what the definition of current flow hinges upon) as being dependent on the charge drift velocity. Because something is dependent on a variable does not make that variable the definition of what that something is - there are other factors in the context, being q, n, and A, that allows the inclusion of drift velocity to derive current flow.

toneboy1

Quote by DragonPetter

They are not different, only different levels of describing the same concept. Kholdstare is explaining the physical description of how it comes about.

In that case I'm intrigued and confused. So it is kind of like a 'compression wave' of charge/time on a grand level but, so on a small level where does Kholdstare's physical description incorporate this?
thanks

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