# Speed of electric signal?

1. Dec 5, 2009

### Phys988

What is the speed of propagation of an electric pulse compared to the speed of light:

- In a normal copper wire.

- In a superconductive wire.

Last edited: Dec 5, 2009
2. Dec 5, 2009

### clem

c......................

3. Dec 5, 2009

### f95toli

Also, the propagation speed in a cable depends on the geometry and the dielectric used; meaning it is doesn't really matter if the cable is superconducting or not*

*expect for the kinectic inductance of the superconductor which should be added to the geometric inductance, but this is a very small effect in a cable.

4. Dec 5, 2009

### xantox

The propagation speed of the signal (which propagates outside the conductor) is practically the speed of light in the material outside the conductor. This is about 0.91c for polystyrene, 0.69c for teflon, and c for air.

Last edited: Dec 5, 2009
5. Dec 5, 2009

6. Dec 5, 2009

### f95toli

Somewhat OT: That analysis is actually not valid for a reak superconductor, what they are actually assuming is that the material is a PEC=perfect electrical conductor.
The full analysis for a real superconductor is more complicated and you need to take the kinetic inductance into account (meaning you need to use the Mattis-Bardeen equations etc).

7. Dec 5, 2009

### SystemTheory

I'm not an authority on superconductors, however, I am confident that the scientific community reserves the term "super" for very special cases of conductors, fluids, states of matter, etc. I agree the All About Circuits reference should use the term "perfect conductor" in its description, and that this is merely an introductory treatment of the transmission line from the perspective of circuit theory.

8. Dec 6, 2009

### patty_24

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