[ajsnigrutin]

Yep, AC is magic.

And not just antennas.... look at computers... at 3GHz (DDR4+ ram), the wavelength is ~10cm, so looking at a single sine wave, you have 1.8volts at the cpu, zero volts 2.5cm away from the cpu, -1.8v 5cm away, zero 7.5cm, and again 1.8 volts 10cm from the cpu... now look at the distance between the cpu and ram, the other frequencies that come with the square(-ish) waves, and all the math to make a basic RAM read/write work.

Just a normal wire (or cable - the simplest component in DC electronic circuits, just a line, that does nothing) changes everything... you send a (voltage) signal in, and the current has to flow at some rate, even before the "signal" (field) reaches the other side of the cable, to "see" if the other end is "open" or soldered together or if some sort of a resistor is soldered there.

[jacquesm]

That's not how current propagates. Current propagates - broken analogy warning - in the same way that marbles would propagate through a tube. You push a marble in on one end and assuming the tube is full another marble pops out the far end. So the flow rate of the electrons is vastly lower than the flow rate of the signal itself!

[ajsnigrutin]

Of course, but currents here are a result of a field that moves those electrons one way or another, and electrons move, before the field reaches the other end (where a resistor is.. or is not.. or a short circuit is), so in your analogy, marbles move down the tube, before they "realize" that the tube is closed on the other end.

[jacquesm]

Fair enough. It's an analogy anyway and it is a broken one in more ways than one (for instance: it doesn't deal with propagation of pulses very well because these can be reflected from the end of the tube, you'd have to model it as a tube full of marbles and springs to account for that) but it serves for some discussion purposes.