In everyday electrical and electronic devices, the signals travel as electromagnetic waves typically at 50%–99% of the speed of light in vacuum.
[1] These interactions are typically described using mean field theory by the permeability and the permittivity of the materials involved.
The purpose of the conductor is thus not to conduct energy, but to guide the energy-carrying wave.
where The velocity of transverse electromagnetic (TEM) mode waves in a good conductor is given by[1]: 360 [2]: 142 [3]: 50–52
As a consequence of Snell's Law and the extremely low speed, electromagnetic waves always enter good conductors in a direction that is within a milliradian of normal to the surface, regardless of the angle of incidence.
In the theoretical investigation of electric circuits, the velocity of propagation of the electromagnetic field through space is usually not considered; the field is assumed, as a precondition, to be present throughout space.
The electric field starts at the conductor, and propagates through space at the velocity of light, which depends on the material it is traveling through.
The corresponding fields simply grow and decline in a region of space in response to the flow of energy.
The latency is determined by the time required for the field to propagate from the conductor to the point under consideration.
In other words, the greater the distance from the conductor, the more the electric field lags.
This is a very large distance compared to those typically used in field measurement and application.
Hence, the intensity of the electric field is usually inappreciable at a distance which is still small compared to the wavelength.
That is, the velocity of propagation has no appreciable effect unless the return conductor is very distant, or entirely absent, or the frequency is so high that the distance to the return conductor is an appreciable portion of the wavelength.
In general, an electron will propagate randomly in a conductor at the Fermi velocity.
When a DC voltage is applied, the electron drift velocity will increase in speed proportionally to the strength of the electric field.
The drift velocity in a 2 mm diameter copper wire in 1 ampere current is approximately 8 cm per hour.
The electrons oscillate back and forth in response to the alternating electric field, over a distance of a few micrometers – see example calculation.