Digital Circuit Boards: Mach 1 GHz

1.5 Voltage and the Electric Field

The force field that exists around any group of charges is called the E or electric field. It is a vector field, as it has intensity and direction at all points in space. The charges (or absence of charge) we will consider are usually distributed on the surfaces of circuit conductors. This force field in the space around charged objects can be sensed by placing a very small test charge in the field. The test charge has to be small enough that it does not contribute to the field being tested. Thus, a test charge is a small accumulation of charge on a small mass.

Work must be done in moving this test charge in an electric field. The work required to move a unit charge between two points is called the potential difference (voltage) between those two points. We usually measure potential difference between conductors. In a radiated field there are no conductors to consider, yet there are potential differences.

Definition: Voltage is the work required to move a unit charge over a distance in an electric force field.

If there are voltage differences, there are electric fields. The converse is also true. If there are electric fields there must be voltage differences. If there are charges on a surface there must be an electric field. Conversely, if there are nonradiated electric fields there must be charges on conductive surfaces.

Voltage differences can exist between points in space or between conducting surfaces. Electric fields exist at all frequencies ...