# How Fast Does an Electric Signal Travel in Different Wires Compared to Light?

• Phys988
In summary, an electric pulse propagates faster in a superconductive wire than in a normal copper wire.
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.

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c......

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.

Phys988 said:
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.

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.

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My recollection is about 0.9c for a DC signal (infinite frequency) in a copper conductor, but I don't recall doing an analysis myself.

This reference treats the transmission line as a superconductor for analysis, and yields results similar to the concept expressed by xantox (note k is the dielectric):

http://en.wikipedia.org/wiki/Wave_propagation_speed

SystemTheory said:
This reference treats the transmission line as a superconductor for analysis, and yields results similar to the concept expressed by xantox (note k is the dielectric):

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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).

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.

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## 1. What is the speed of an electric signal?

The speed of an electric signal refers to how fast an electric current can travel through a medium. It is typically measured in meters per second (m/s) or feet per second (ft/s).

## 2. How is the speed of an electric signal determined?

The speed of an electric signal is determined by the properties of the medium it is traveling through, such as the type of material, its temperature, and its density. It is also influenced by external factors, such as the presence of obstacles or interference.

## 3. Is the speed of an electric signal constant?

No, the speed of an electric signal is not constant. It can vary depending on the medium it is traveling through and other external factors. In a vacuum, the speed of an electric signal is constant and equal to the speed of light (299,792,458 m/s).

## 4. How does the speed of an electric signal compare to the speed of light?

In most cases, the speed of an electric signal is slower than the speed of light. However, in certain materials with high conductivity, such as copper, the speed of an electric signal can approach the speed of light.

## 5. Can the speed of an electric signal be increased?

Yes, the speed of an electric signal can be increased by using materials with higher conductivity, reducing the distance the signal needs to travel, and minimizing external factors that can slow it down. However, it cannot exceed the speed of light in a vacuum.

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