Establishment of Current in Conductors

Currents are established on the surface of conductors by the propagation of electromagnetic waves in the insulating material between them. If the load is less than the characteristic impedance of the line, multiple reflections and retransmissions eventually build up the line current to that required by the load. The currents are initially established on the surface of the conductors before diffusing relatively slowly into the interior. These transmission and diffusion processes are fundamental to basic electrical engineering science, and their effects can be observed by applying a step input to a loaded line, and observing the load and mid-line voltages. The mid-line voltage clearly shows how the diffusion effects the propagation and reveals that the initial build up of surface current causes cables to enter a diffusion limited mode where currents have to diffuse into the interior before further propagation can take place to replenish surface currents.