What's the relative speed of electricity?

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SUMMARY

The speed at which electricity activates a device is determined by the propagation of the electrical signal through the transmission medium, such as an extension cord. When a plug is switched on, the signal travels at approximately two-thirds the speed of light, influenced by the dielectric constant of the insulating material. This means that in a perfect scenario, the light in London would turn on almost instantaneously after the switch is flipped in St Andrews, with a slight delay based on the specific characteristics of the extension cable used.

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  • Understanding of electrical signal propagation
  • Knowledge of dielectric materials and their properties
  • Familiarity with transmission line theory
  • Basic concepts of speed of light in different media
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  • Research the effects of dielectric constant on signal speed in cables
  • Learn about transmission line theory and its applications
  • Explore the speed of electromagnetic waves in various materials
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Electrical engineers, physics students, and anyone interested in the principles of electrical signal transmission and its practical applications in real-world scenarios.

Magma828
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I've searched for this question on these forums and google and everyone seems to have the same question as me, but hasn't stated it clear enough for people to understand exactly what they want to know.

I'm wondering how long it takes for electricity to turn something on. I don't want to know how fast electrons flow because I know all about electron drift velocity, and this is clearly nowhere near the speed at which electricity takes effect.

Put it this way:
I have a massive extension cable which I connect from from my house in St Andrews to London. The dude in London has a light plugged into the end of the extension cable. When I switch the plug on, how long will it take for the guy to see the light turn on?

Also, please don't reply stating the flaws in my experiment - just imagine everything is perfect and we have super-accurate measuring equipment.
 
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The simple answer to your question is that the extension cord will behave like a transmission line, and the signal will propagate through the line at somewhat less than the speed of light, with the ratio of the speed of the signal to the speed of light depending on the relative dielectric constant of the insulating material between the wires in the extension cord. Try this link for an explanation:

http://www.allaboutcircuits.com/vol_2/chpt_14/2.html

http://www.allaboutcircuits.com/vol_2/chpt_14/3.html
 
The signal speed in a high quality cable is about 2/3 the speed of light.
 

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