Well, all you (!) hopefully have switched on or off an electric appliance in their life . What happens when you do that? No, don't tell me that it brings electricity to an electric appliance. I know it does, but what actually happens?
The answer lies in this
paper, published by the renowned Scottish Physicist, James Clark Maxwell in 1861. The laws that he formulated from various laws existing at that time connecting electric fields and magnetic fields became the basis for what is known as Electromagnetism. He was the one who unified the previously separate forces of Electricity and Magnetism. His equations, actually extension of Gauss Law, Ampere's Law and Faraday's law gave all that was to be known of an electromagnetic transmission.
Maxwell's equations theoretically predicted the existence of electromagnetic fields and electromagnetic propagation. But it was only years later that Henrich Rudolf Hertz succeeded in generating and detecting Electromagnetic waves.
Now, Electromagnetic wave has some interesting properties. Consider a wave travelling along a perfect conductor. The propagation constant of such a wave has a real part, often denoted by α, which is a measure of its attenuation. For a perfect conductor, α has a value which highly dampens the EM wave, once its frequency gets high. Now the inverse of α, ie (1/α) denotes the quantity called skin depth. Skin depth is a measure of distance that the wave can travel inside a conductor before it gets attenuated to a considerable extent. Thus we see that propogation of an Electromagnetic wave takes place only on a thin outer layer, commonly and literally referred to as the skin. This effect is called the skin effect and its applications are multifarious.
Now, what happens when you switch on that devicce? The current flows due to a potential difference between the source and load in the form of an electric field. As soon as the switch is on, an electric field is established throughout the wire, starting from one end. The direction of the field is radially outward, resulting in a magnetic field around the conductor. The direction of the magnetic field is anticlockwise(when looking from source end). Hence a disturbance quantified by the Poynting vector, E x H begins to propogate along the direction of E x H. ie in the forward direction, when looking from the source end. This disturbance establishes the electric field everywhere. Thus the electrons present in this field experiences a force which makes them move and hence conduct. Thus we see that conduction actually takes place at the speed of light !
So, the next time you switch on, remember, you are generating Electromagnetic waves around !!!