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A condition in space in the vicinity of an electrically charged body such that the forces due to the charge are detectable. An electric field (or electrostatic field) exists in a region if an electric charge at rest in the region experiences a force of electrical origin. Since an electric charge experiences a force if it is in the vicinity of a charged body, there is an electric field surrounding any charged body. The electric field intensity (or field strength)E at
a point in an electric field has a magnitude given by the quotient obtained
when the force acting on a test charge q' placed at that point is divided
by the magnitude of the test charge q'. Thus, it is force per unit charge.
A test charge q' is one whose magnitude is small enough so it does not
alter the field in which it is placed. The direction of E at
the point is the direction of the force F on a positive
test charge placed at the point. Thus, E is a vector point
function, since it has a definite magnitude and direction at every point
in the field, and its defining equation is Eq. (1).
D in a dielectric (insulating)
material is related to E by either of the equivalent equations shown as Eqns.
(2), where P is the polarization of the
medium, and In addition to electrostatic fields produced by separations of electric charges, an electric field is also produced by a changing magnetic field. |

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