What Electrical Circuits Look Like to Me

[Gryphon]

Technically, speed of individual electrons is about 1 cm per second IIRC, everything happens very fast because every electron "pushes" one next to him, like a PCB tube full of marbles - you push the end marle and first marble falls out instanty, and speed of individual marbles is very small actually.

Seriously!? Thats sweet! I knew the whole they push the one next to them so theres basically no delay in
electrical transfer, but i didn't know that the speed at which electrons are displaced was that slow.

 

[Eudaimonium]

Seriously!? Thats sweet! I knew the whole they push the one next to them so theres basically no delay in
electrical transfer, but i didn't know that the speed at which electrons are displaced was that slow.

Yeah I believe our physics teacher brough that up, something among the lines off : "Next cup of coffee on me if you tell me the speed of electronics in electrical circuit" , and we're all like "Speed of light" then he surprised us by that fact.

Trying to dig it up on wiki to confirm.

 

[pullbangdead]

Individuals electrons are moving very slowly, here's an example calculation of the drift velocity:

How fast do electrons drift?

We can get an idea of how fast the drift velocity is by taking some typical values of current and wire dimensions.

Let's think of a current of 5 A that is flowing in a copper wire with a cross section of 0.5 mm2 (= 0.5 * 10-6 m2)

For copper, n = 8.5 × 1028 per m3
The charge on an electron, Q = 1.6 × 10-19 C

So,
I = n A v Q

5 = 8.5 × 1028 × 0.5 × 10-6 × v × 1.6 × 10-19

5 = 27 200 v

v = 7.35 × 10-4 m s-1

So, for this current, the drift velocity of electrons is about a tenth of a millimetre per second: pretty slow!

The analogy of marbles pushing through isn't a complete analogy though.

The real explanation is that electrons are being accelerated by the applied field, and they accelerate until they hit something, ie scatter, which slows them back down again. So you get electrons accelerating, scattering, accelerating again, scattering again, giving you an average drift velocity. The field is moving through the conductor fast, at almost the speed of light-ish, but the drift velocity of the electrons is much smaller through the material due to scattering. That's why conductivity of metals decreases as temperature increases: higher temperature gives more thermal vibrations of atoms in the material, which increases the frequency of scattering events, which means the average drift velocity of the electrons goes down.

 

[Xplorer877]

Hmmm I think I've built that circuit before. If I remember correctly it's a schematic to a machine that makes dehydrated water. No, actually, it's a circuit for a calculator that can divide by zero, thats right...

I like that "NOT A RESISTOR Wire just does this" part. Hahaha!!!

-Tony

 

[Eudaimonium]

Individuals electrons are moving very slowly, here's an example calculation of the drift velocity:



The analogy of marbles pushing through isn't a complete analogy though.

The real explanation is that electrons are being accelerated by the applied field, and they accelerate until they hit something, ie scatter, which slows them back down again. So you get electrons accelerating, scattering, accelerating again, scattering again, giving you an average drift velocity. The field is moving through the conductor fast, at almost the speed of light-ish, but the drift velocity of the electrons is much smaller through the material due to scattering. That's why conductivity of metals decreases as temperature increases: higher temperature gives more thermal vibrations of atoms in the material, which increases the frequency of scattering events, which means the average drift velocity of the electrons goes down.

Well the marbles analogy helps people understand why all street lights light up at the same time while each electron is travelling at 1/10 mm per second , which is ten times less than what I've heard.

They are even slower Wow.

 

[dnar]

Thats a funny schematic. I spotted it on Hackaday a few weeks ago, it is stuck on my office wall.

LOL @ the Arduino for Blog cred.

 

[flecom]

lol @ the "Magic Smoke" container!

I printed this out and its going in my office

 

[fullinfusion]

Haha that's awesome! :bowdown: