The electric field intensity vector E is
the force that would act on a unit test charge
if this charge is inserted in the volume where
the electrostatic field exists, .
It is a normalized measure of the strength of the
field and its direction.
In a linear medium,
the principle of superposition holds. According
to it, the electric field at an observation point
is the vectorial sum of the individual
contributions (fields) of all present charges
in the region of interest, .
In the set-up below,
we have two point charges (red and blue points),
whose individual E-field vectors at the
observation point P are given by

where is the i-th charge value, is
the distance from the i-th charge to P,
and is
the unit vector pointing from the i-th
charge toward P.
The values of the
charges are fixed. You can, however, change the
sign of the second charge .
Click on the observation point (black point),
and drag to any location within the shaded area.
Observe the strength and direction of the overall
field vector E (the black arrow). To appreciate
better the vectorial nature of this superposition,
the individual field vectors, and (red and blue arrows, respectively), are
also plotted.
Since this is a 2-D
planar illustration, the motion of the observation
point is limited to a plane. These interactive
plots, however, fully represent reality, since
the three charges—the two sources and the
test-charge—always define a plane (unless
they are perfectly aligned in a line), which
contains all three field vectors. |
|
|