The Electric Field

The electric field is simply a label attached to every point in space. It gives the magnitude and direction of the electric force which a charge of +1 Coulomb would experience at that point.
One can measure the electric field directly by observing the electric force on a little test charge at different locations.

The electric field is defined as

                      electric force      Newtons
                 E  =  -------------      -------
                          charge          Coulomb

One can calculate the electric field due to a point charge:

                              charge
                 E  =  k * ------------
                           (distance)^2

The electric field lines point away from a positive charge (because a charge of +1 C would move away from it) and toward a negative charge (because a charge of +1 C would move toward it).
The electric fields due to several particles simply add together in a vector sense (component by component).

One can calculate the electric field between two uniformly charged plates (which are much larger than the distance between them):

                           Q
                 E  =  --------
                       eps * A

where

              Q   =   magnitude of the charge on each plate
              eps =   permittivity of free space
                  =   8.854 x 10^(-12)    C^/N-m^2
              A   =   area of each plate

The electric field between parallel plates doesn't depend on the distance away from either plate.

Viewgraph 1