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Electric, magnetic and electromagnetic fields in everyday life
 
- Physical basics
- Electromagnetic fields in the human environment

Electric fields

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An electric field originates from an electrical potential difference between two charge carriers, which is called electric voltage U and the unit is volt (V). Electric voltage can occur without current flow. The unit of the electric field strength is volt per meter (V/m). The intensity of the electric field increases with higher electric voltages and it decreases with growing distance from the source. If the intensity of the electric field is stable in magnitude and direction, it is a homogenous field as it occurs e.g. in a plate capacitor.

Homogenous electric field between the plates of a capacitor

Conversely, in an inhomogenous electric field, magnitude and direction depend on the location (e.g. in a two-core power cable; generally with a dipole).

Inhomogenous electric field of a dipole (e.g. two-core power cable, here shown in cross section)

Electric fields are strongly influenced by their environment. Every conductive object can change the electric field. This can be explained by electrostatic induction, when under the influence of an electric field a transfer of charge distribution occurs in a conductive object. In a closed and conductive cage (“Faraday cage”) the electric field inside is practically zero. Also buildings can act as a shield, so that the electric field strength inside a building is negligibly small compared to the external electric field strength. Conversely, an electric field inside a conductive object (e.g. microwave oven) can be shielded almost completely to the outside world.

Full insulation by a Faraday cage: rearrangement of charges in the metal of the cage by moving of the positive and negative charges to opposite sides. This leads to a cancellation of the field inside the cage, because the resulting opposing field inside the cage superimposes the external field and exactly compensates it.

When a concuctive object is exposed to a time-varying field, the constant charge exchange creates an alternating current in the object with the unit Ampere (A). The rate of charge transfer per unit area is called electric current density with the unit ampere per square meter (A/m2).

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Glossary: alternating current, ampere, charge carriers, current, dipole, electric, electric current density, electric field, electric field strength, electric voltage, exposed, Faraday cage, homogenous, induction, leads, microwave oven, potential, power, volt