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Comment by curiousgal

6 years ago

I am surprised that signals travel faster in copper (3c/4) than in fiber (2c/3), anyone has an explanation?

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curiousgal

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chongli  6 years ago

The number for copper is not a fixed quantity, it varies with the type of cable. Electric fields are outside of the copper wire, not inside. The copper conductor acts as a wave guide for the electromagnetic wave. So it turns out that things around the cable have an effect on the speed of propagation [1], particularly the insulator. Bare copper wire in a vacuum would be very close to c. In the case of fibre, the issue is index of refraction.

[1] https://en.wikipedia.org/wiki/Velocity_factor