What is Electricity? - Part Two

So I intimated I was going to reveal why the bulb is illuminated almost instantaneously when you flip the switch, despite the fact that electrons move very slowly in the wire.....

In fact, the speed of the signal along the wire is the same as the speed of light.

"How can this happen?" I hear you ask.

Well, liken the wire to a small tube, packed with wet sand. Yes, wet sand. The sand cannot be compressed any more.

Shove your hand in one end. If you are strong enough, the sand at the other end will move, almost immediately after.

But the sand grains within the tube will not have moved even a centimeter.

This is the principle of Electricity. The electrons are so numerous and are all along the wire, so that if one electron is "pushed" at one end, the others respond by pushing "along the line" so to speak.

Like a slinky.

A "wave" of "pushness" goes along the wire, and, because this is electrostatics, it moves at the speed of light.

Hence the "almost" immediate response at the bulb.

Something like a "Mexican Wave" in the crowd at a soccer match. No two people ever move very far, but the wave goes through the crowd very fast compared to the movement of the people.

Which brings me to the point about phase velocity versus group velocity, a recent argument I had with a Doctor of Physics in the physics room, but THAT is another topic!