Richard wrote:
Electrons move in a conductor very slowly. Far, far, below the speed
of light.

So, when you put a voltage or a source of electrons (which have charge
and eminate their own tiny electric field) at one end of a conductor,
what exactly propagates through the conductor, so that the voltage at
the end of the conductor appears (i.e. becomes measurable) in a time
suggesting propagation of the voltage (or charge) at near light speed?


Charge.

Put a row of marbles or ball bearings on a table. Roll another one so it
strikes the near end of the row, and notice that one leaves the far end
very quickly. A unit of momentum (a rolling ball) hits the near end, and
that unit of momentum propagates to the far end and appears in the form
of a rolling ball there, much more quickly than the balls themselves
roll. In this case, the momentum of the ball is propagating very quickly
from one end to the other.

Similarly, a unit of charge (analogous to the momentum of the rolling
ball) propagates much faster than the electrons. Put a unit of charge in
one end, and a unit of charge pops out the other at near the speed of
light, while the electrons themselves move at something like a few miles
per hour.

Roy Lewallen, W7EL