Electric displacement field

The electric flux density - also electrical excitation, dielectric displacement or dislocation density called - describes the density of the electric field lines in relation to an area A. It is a physical quantity of electrostatics and electrodynamics, designated by the symbols and according to the international system of units in the unit Coulomb per square meter ( C / m ) specified.

This with the surface charge density σ consistent, however, the electric flux density is - unlike those - a vector, ie directed quantity.

Exists between two points in space and an electrical voltage, then one speaks of different potentials in and. In between are called equipotential surfaces. These are closed surfaces each with a constant potential. At right angles to these equipotential surfaces are the electric flux lines. By definition, the positive charges are the source of electrical flow, the negative charges of the sink.

The electric flux passing through an arbitrary area A is equal to the surface integral of the electric flux density D process that transmits only electric flux component that is normal to the surface A, the electrical flow through the area A in. Mathematically expressed by vectors and by the operation of the scalar product ( inner product ) as this circumstance:

The electric flux through a closed surface is thus equal to the area enclosed by this surface electric charge.

The change over time of the electric flux density has a displacement current in the extended Maxwell law Ampère.

Related to the electric field intensity

The electric flux density can be generally described as the sum of the polarization and of the product of the electric field with the electric field constant write ( dielectric constant / permittivity of vacuum ), ie:

In the case of vacuum, the polarization disappears, so is the electric flux density (also called sliding flux density ) in a simple relation with the electric field strength. In free space, the following applies:

In the simplest case of a linear isotropic medium is changed, the relationship between the electric flux density and the electric field strength to the relative permittivity of the dielectric in which the electric flux density is measured, so that there is a general relationship:

In the case of an anisotropic medium, the electric flux density shows no longer necessarily in the direction of the electric field strength. Slopes of the two linear sizes together, so can specify a tensor of second stage as a unique proportionality.

A result of such a connection is the birefringence. Single crystals typically show linear anisotropic behavior. An example of non-linear behavior between the electric field and river provide ferroelectrics represent that retain some of their polarization after the application of a strong field.

Other examples of non- linear relationship between the electric flux density and electric field strength can be found in nonlinear optics.

Electric flux density in the plate capacitor

The plate capacitor with parallel plates is the electric flux density in the direction of the surface normal of the capacitor plates. Your sum is:

Here, the amount of charge of a plate capacitor and the surface of the respective plates. Alternatively, the review because of the proportionality of electric field strength and surface charge density as