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Muroid t1_itzzcye wrote

Electricity travels through wires at a high percentage of the speed of light, but not at the speed of light.

Same applies to light in fiber optic cables, actually.


OpenGiraffe t1_iu00sq9 wrote

The light in fiber optic cables travel at the speed of light, don't they?

Only, not the characteristic speed of light in vacuum, c≈300 000 km/s. You have to take the refractive index into account. But it's still the speed of light, through that specific medium (fiber optic cable in this case).


Muroid t1_iu01r1h wrote

The speed of light almost always refers to c. It would technically be correct to refer to any speed that light travels at as “the speed of light” but given the common name of c, that is almost never what people mean or understand by the phrase “speed of light” unless it’s been very clearly specified.

The speed of light through air is very, very close to c. The speed of light through fiber optics isn’t. Still a high percentage of c so very fast, but not a value that you’d ever mistake for c. With air it’s practically a rounding error away.