Charge, Capacitance and the Transmission Line

A charged plate of a capacitor causes electrons to jump from the more negative plate towards the positive plate. There is very little conductance so most of the electrons ultimately make a round trip. Understanding the electron dynamics helps to understand how capacitors really work.

Dielectric materials are not conductive. If an electron moves into a dielectric kinetically it will be replaced by an electron from the dielectric. The electrons swap places. When a capacitor begins to charge the energy from the swapped electron is far less than the electron moving into the dielectric with significantly more kinetic energy. As time progresses the electrons in the dielectric contain more and more energy in the form of root mean squared velocity until the capacitor is fully charged. At this point the electrons in the dielectric contain enough energy to keep the electrons on the plate stimulated.

The telegrapher's transmission line model has a shunt capacitance. A small proportion of electrons flowing out the dielectric of a conductor will be replaced by electrons from the dielectric. This constant replacement charges the dielectric around the conducting medium. Capacitance, inductance and conductance all describe how electrons leave a transmission line and interact with the surrounding dielectric.