Electric field intensity
The strength of the electric field is measured using a quantity called the electric field intensity. The
greater the electrical field intensity the stronger the field. The electrical field intensity
(E
E) is defined as:
In a uniform field the electric field intensity is constant (the same at any point in the field) while in a
radial field the electric field intensity decreases as the distance from the central charge increases.
Therefore for a radial field the electric field intensity distance d from a positive charge of size Q
coulombs is:
For a uniform field between two parallel plates separated by a distance d and with a potential
difference V between them the field is:
the units for electric field intensity are Newtons per coulomb (NC
-1).
Units for electric field intensity
An alternative unit for electric field intensity may be derived as follows.
Since Joules = Volts x coulombs = Newtons x metres (J = VC = Nm) we can write NC
-1 as
[VC/m]C
-1 = Vm
-1. The electric field intensity may also be expressed in volts per
metre (Vm
-1).
Using these units it is probably easier to get a feel of what electric field intensity is, the change of
voltage with distance (see later). The bigger the field the more rapidly does the potential change
with distance. Think about this if you are near a Van de Graaff generator and your hair stands on
end.
