I am reading "Radio Theory Handbook" and am confused with the statement that says that electrons are moving through the wire at snails pace.But it goes on to say the "electrical effect" is instantaneous. I assume he means the speed of light. Then what is this mysterious electrical signal in the wire that moves at the speed of light? Is it the EMF? By definition electricity is the flow of electrons. But yet the electrons are said to travel slow? There cannot be a contradiction. I am asking for help in clarifying this. Thank you. There is another question " Is voltage the speed of the electrons? This is not the same question. I am not asking about voltage. I am asking about the apparent contradiction given the fact that electricity which is the flow of electrons has an almost instantaneous effect while the electrons themselves more very slowly. Although it is not the same question there was enough useful information there and along with all the excellent responses that my question has been well explained.
The electrons zip about at random due to thermal energy (more properly at the Fermi energy, once you start thinking in quantum terms). However that random motion has no net effect on the large scale, other than to generate Johnson noise.
Superimposed on this random motion is the drift velocity, which is a snails pace, due to the macroscopic current. Each 64g or so of copper has a faraday of charge in its free electrons (96500 coulombs), so they don't have to move fast to create a large current.
The electric and magnetic fields move at the speed of light in the insulating medium around the wire and this is what carries the signal and controls everything - the current in the wire responds to the electric field, starting at the surface and working down into the bulk of the metal according to the skin-effect.
At radio frequencies all the current is carried in the outer most few microns of the conductor, pretty much all the action is in the space or insulator around the wire (or inside the waveguide)
It is changes in the fields inside and around the wire that travel at the speed of light. Imagine the wire as a hollow tube full of electrons. When there is no current the electrons are all sitting there, repelling each other, but since there is nowhere to go, they just sit still.
When an electron at the back of the wire starts getting pushed (by a battery for example), it gets closer to its neighbors in front, which then pushes them forward. These electrons start to move, which then causes them to start pushing on their neighbors. Eventually all the electrons are moving down the wire.
The speed with which the electrons hear about their neighbors moving determines how quickly the signal travels down the wire. Nothing about this process actually requires the electrons to actually go anywhere quickly, just that their neighbors feel changes quickly.
This is all a huge simplification, in reality there is a continuous electric field, and there is a magnetic field generated around the wire, and of course the wire isn't hollow, but this picture can help for getting the concept.
Could we analogise it to something like this? Imagine a really long train with a huge number of coaches. The engine begins to move, very, very slowly. Instantly, the last coach also begins to move. The speed of the engine has no relation whatsoever to the speed at which the information of the train starting to move is propagated.
The electrons are like the coaches.
Electrons themselves move at the glorious speed of fractions of a millimeter per second. However, they are so close to each other that they are constantly bumping in to each other. This makes an electrical signal travel down a wire at somewhere usually around 2/3rds the speed of light. That speed can be effectively slowed by various circuit elements as well. A signal inside a coaxial cable will travel more slowly than a signal in a free-hanging wire. See wikipedia on the Velocity Factor for more details about this, specifically part about the velocity factor in a lossless transmission line.
As for "electrical effect", he's probably talking about the electromagnetic radiation that can be produced by certain oscillations in circuits (changes in the electrical field resulting in radio waves, electrons moving between energy states in LEDs, etc). These travel at the speed of light in a vacuum because electromagnetic radiation is light and vice versa.
Yes, 1) electrons travel extremely slowly, and in AC systems they constantly halt and reverse direction, 2) metal wires are always filled with enormous amounts of electrons, 3) batteries and generators are electron-pumps, and they don't create or 'generate' the electrons being pumped.
The 'mysterious signal' is exactly that. It has various names: electric signals, electromagnetic energy, electrical waves, EM waves. It travels at the speed of light because it IS light/radio/EM. If we have a ring of movable electrons (a metal circuit,) and if we suddenly apply a pumping-force at one spot, electromagnetic waves will spread throughout the circuit at the speed of light, until all of the metal's charges 'get the message' and begin moving.
Similar question: what do electric companies sell? Not current, since the path for current is a closed loop. They sell 60Hz radio waves, but waves being sent over transmission lines and absorbed by distant motors and lights. Inside your home wiring and inside the long transmission lines, electrons vibrate back and forth, but the EM waves proceed continuously forward. Don't mistake the "medium" for the "waves." In empty space, light and radio requires no medium, but if electromagnetic waves are traveling along wires, the movable electrons act as the "medium" for EM wave propagation.
Here's one confusing aspect: the flow of EM waves has no frequency limit, and operates all the way down to zero Hz. The EM-fields description of 2-wire transmission lines will also apply to flashlights. When a battery is lighting a bulb, EM waves are traveling from battery to bulb at the speed of light. This effect becomes obvious for 100MHz signal generators, but it remains the same for 60Hz and for DC. In DC systems we can only detect the high-speed energy-flow if we suddenly start or stop the flow, to produce a sharp edge which can be tracked. And so, another name for your mysterious signal could be: "DC wave-energy!" :)