Electric field

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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).

E = F/q' (1)

Electric flux density or electric displacement 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

D =ε0 E+PD = ε E (2)

medium, and ε is the permittivity of the dielectric which is related to ε0, by the equation ε = kε0, k being the relative dielectric constant of the dielectric. In empty space, D = ε0E.

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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