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

  • Context: Undergrad 
  • Thread starter Thread starter Phys988
  • Start date Start date
  • Tags Tags
    Electric Signal Speed
Click For Summary

Discussion Overview

The discussion centers on the speed of propagation of electric signals in different types of wires, specifically comparing normal copper wires and superconductive wires to the speed of light. It explores theoretical aspects, practical implications, and references to external resources.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • Some participants propose that the speed of propagation in a normal copper wire is approximately 0.9c for a DC signal, although this is based on recollection rather than direct analysis.
  • Others argue that the propagation speed in a cable is influenced by the geometry and dielectric material, suggesting that superconductivity may not significantly alter the speed compared to conventional materials.
  • A participant notes that the propagation speed of the signal outside the conductor approaches the speed of light in the surrounding material, providing specific values for polystyrene, teflon, and air.
  • There is a mention of the kinetic inductance of superconductors and its minor effect on propagation speed, indicating that a more complex analysis is required for real superconductors.
  • One participant questions the validity of a referenced analysis that treats superconductors as perfect electrical conductors, suggesting that the full analysis involves more complex equations and considerations.
  • A high school student seeks resources for physics investigatory projects related to electricity, indicating a need for accessible information on the topic.

Areas of Agreement / Disagreement

Participants express differing views on the impact of superconductivity on signal propagation speed, with some emphasizing the importance of dielectric properties and geometry, while others focus on the theoretical aspects of superconductors. No consensus is reached on the exact propagation speeds or the validity of referenced analyses.

Contextual Notes

Limitations include the dependence on specific definitions of superconductivity and the assumptions made in referenced analyses. The discussion also highlights the complexity of analyzing real superconductors compared to idealized models.

Who May Find This Useful

This discussion may be useful for students and enthusiasts interested in the physics of electricity, signal propagation, and the properties of different conductive materials.

Phys988
Messages
16
Reaction score
0
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:
Physics news on Phys.org
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.
 
Last edited:
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://www.allaboutcircuits.com/vol_2/chpt_14/3.html

For an informal discussion see also:

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):

http://www.allaboutcircuits.com/vol_2/chpt_14/3.html
[/url]

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.
 
hi...I'm a high school student...i just want to ask if you know some websites that I can use to find my project..?..it is all about physics investigatory projects that are related in electricity...I just need this..as soon as possible...I tried some websites..but its all common...just like in..miniscience.com..do you know some more??..thank you..
 

Similar threads

Undergrad How Fast Does an Electrical Impulse Travel in a Copper Wire?
  • · Replies 100 ·
4
Replies
100
Views
11K
High School Switch-to-lightbulb wire delay
  • · Replies 5 ·
Replies
5
Views
2K
Undergrad Speed of Electricity in Plate Capacitor & Cable
  • · Replies 18 ·
Replies
18
Views
2K
Undergrad How does the Hall effect interact with the iLB force in a copper wire?
  • · Replies 24 ·
Replies
24
Views
2K
Undergrad Does electricity have a propagation delay?
  • · Replies 18 ·
Replies
18
Views
2K
Undergrad Electrical signals -- How do they actually propagate in real wires?
  • · Replies 7 ·
Replies
7
Views
3K
Undergrad How is Potential Difference Created across a Resistor?
  • · Replies 21 ·
Replies
21
Views
4K
Undergrad What accelerates the light back to its constant speed?
  • · Replies 5 ·
Replies
5
Views
1K
Undergrad Identical Wires with different voltage--does electron behavior differ?
  • · Replies 19 ·
Replies
19
Views
2K
Undergrad Spreading of electric current -- start signals in a circuit
  • · Replies 8 ·
Replies
8
Views
2K