To answer this, we must descend to the depths of matter, made up of atoms made up of protons with a positive electric charge, neutrons without charge, and electrons with a negative charge. The electricity that circulates through conventional copper cables is made up of the movement of free electrons – the protons and neutrons remain stationary – which, to the surprise of the layman, have a very slow displacement speed .
In a copper cable with a current density of 10 amperes per square millimeter (typical of common installations), its speed is less than one millimeter per second.
So why do the lights in our house turn on as soon as we press the switch? This speed occurs because the free electrons that transfer the electricity are present throughout the circuit in an inconceivably large number and density. An analogy allows you to understand it very well: think of a tube full of marbles.
If we put one more in, another immediately comes out to make room for it, no matter how far away it is. Electrons behave the same way in a wire, no matter how long it may be: if one of them moves, even very slowly, all the others have to. The effects of electricity occur instantly, and that is why we say that the speed of current in a wire is close to that of light.
