What is the speed of electric flow?

[Dims]

Hi! What is the speed of electric flow? I mean not a speed of electron drift, but a speed of spreading of electric perturbation over normal metallic wire?

 

Can you explain prove your answer or give some links to experimental data?

 

Thanks.

[CPL.Luke]

if you mean how fast elecrons become aware that there is a voltage present in the wire, then that would be the speed of light in the medium (as this is the speed at which electric fields change)

[Dims]

But what is the speed of light in copper?

 

I mean the following. Let us have short circuited copper wire 1 meter length. Then we induce some current at first place of that wire. After what time the current (in ampers) at other edge will be at least 2/3 of that at another?

[Klaynos]

But what is the speed of light in copper?

 

I mean the following. Let us have short circuited copper wire 1 meter length. Then we induce some current at first place of that wire. After what time the current (in ampers) at other edge will be at least 2/3 of that at another?

 

The speed of light in that material. And I'm pretty sure that Iin will = Iout, or there abouts as the resistance is quite low.

[Dims]

So what is the speed of light in copper?

[Klaynos]

http://en.wikipedia.org/wiki/Permittivity#Permittivity_in_media

 

[math]\epsilon \mu = \frac {1}{v^2}[/math]

[swansont]

The index, and thus propagation speed, depends on the wavelength (and frequency). For copper, the generally quoted value is about 225,000 km/s, or often rounded to 2/3 c, for RF, which probably also applies to electric current flow.

[psynapse]

Nvm re-read, not drift velocity :0

[Dims]

For copper, the generally quoted value is about 225,000 km/s, or often rounded to 2/3 c

Is it possible to calculate this value somehow? Does inductance play role here? Or is it just measured directly? Can one read the setup of experiment?

[Klaynos]

Is it possible to calculate this value somehow? Does inductance play role here? Or is it just measured directly? Can one read the setup of experiment?

 

If you know the permativity and permiability of the material you can apply the equation I gave above where v is the phase velocity of light in a meduim. If you put in epsilon 0 and mu 0 you get out c.

[Dims]

How can I get c? It will be infinity in that formula.

 

And what is permittivity applying to a metal?

[Klaynos]

How can I get c? It will be infinity in that formula.

 

And what is permittivity applying to a metal?

 

No it wont.

[math]

\epsilon \mu = \frac {1}{v^2}

[/math]

 

[math]

\sqrt {\frac {1}{\epsilon \mu}} = v

[/math]

 

[math]

\sqrt {\frac {1}{\epsilon_0 \mu_0}} = c

[/math]

 

[math]

\sqrt {\frac {1}{8.854 * 10^-12 * 4 \pi *10^-7}} = c

[/math]

 

Finding epsilon and mu for a metal can be done. I can't remember how, a quick google should tell you though.