Many people made the “long cable” joke; only one person did the maths.https://twitter.com/SimonKoppel/status/1016245526910693376 …
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5%?! More like 50%. speed of light = 1 / sqrt(relative permittivity * vacuum permitivity * relative permeability * vacuum permeability), and 4 is usually a good first estimate for relative permittivity * relative permeability for materials we don't know anything about.
Also, regarding "speed of light in copper": This is nonsensical. The electromagnetic wave isn't propagating in copper, it is propagating in the insulator between the two conductors. That's why speed on a PCB is defined by PCB material, not conductor.https://twitter.com/TheMerovius/status/1016247969333510144 …
