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Theory:
An
electric field
is a region in space in which electric forces act on electric charges,
if present.
The electric field strength for any point in space is defined as the net
electric (Coulomb) force per unit of positive charge acting on a charge placed at that
point, i.e.,
q
F
E
r
r
=
[1]
The SI unit for electric field is newton / coulomb, or (more practically) volt/meter.
The direction of an electric field at any point is defined as the direction of the net
electric force on a positive
charge placed at the point.
Faraday introduced the concept of
lines of force
to aid in visualizing the magnitude
and direction of the total electric field about a charge or collection of charges.
Some
of these concepts are listed below.
The lines of force originate on a positive charges and terminate on negative
charges.
The density of the lines of force in a region of space is used to represent the
electric field strength in that region of space.
Lines of force will not cross over or touch one another.
Electric fields can be represented by a scaled drawing, by first choosing a scale factor
(proportionality factor) so that
n
number of lines/cm
2
represent a certain value of
field strength(volts/m).
(
a
)
(
b
)
Figure 1
Examine the figure 1.
The two figures represent a uniform electric field. If we let
figure 1(
a
) represent an electric field with a field strength of
E
, figure 1(
b
) would
represent an electric field with a field strength of 2
E
. (There are twice the number of
field lines within the same general area)
It is possible to find any number of points in an electric field, all of which are at the
same potential (voltage). If a line or surface is constructed such that it includes all
such points, the line or surface is known as an
equipotential
line
or surface.
A
charge may be moved along such a line or surface without the expenditure of work.
The surface of all conductors are equipotential surfaces.
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 Spring '08
 Staff
 Charge, Electric Fields, Force

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