How is the electric field built up?

Electric field (E-field)


The space between two unequally charged objects is called an electric field. In this space, an electrical charge exerts a force on another charge.
The strength and direction of the electric field is shown by field lines (arrows). The direction of the field lines runs from plus to minus. The direction of the field lines determine the forces that act on objects in the electric field. In this way, bodies and charges can also be changed locally.
The electric charge that creates the electric field is e.g. B. generated by an electrical voltage. This principle is used in the capacitor.

Electric field strength E

In a homogeneous electric field, the electric field strength is the same everywhere. The level of the electric field strength depends on the size of the charge difference and the distance between the charged parts.
The electric field strength E is the greater,

  • the greater or more unequal the electrical charges or the greater the electrical voltage.
  • the smaller the distance between the charged bodies.

Formula symbol

The symbol for the electric field strength is the capital E.

Unit of measurement

The electric field strength depends on the voltage and the distance between two bodies. Therefore the unit of measurement is kV / mm, V / m or V / cm.

Formula for calculation


Dielectric strength

If the electrical charge is too large or the distance is too small, an exchange of charges takes place. The energy released in the process can be very large. The charge exchange is noticeable by a bang and an arc.
Different substances can prevent the exchange of charges between two charges. The field strength that these substances withstand until they break down is called dielectric strength.

If the dielectric strength is exceeded, the electrons in the electric field accelerate so strongly that when they collide with neutral atoms, ions and electrons are formed.
The dielectric strength of air also depends very much on the properties of the electrodes. If two pointed electrodes are facing each other, 1 kV is sufficient for the spark to flash over. This is due to the fact that the electric field is strongly condensed at the tips and thus facilitates ionization. A glow discharge occurs just below the breakdown voltage (bluish weak light in the dark room) and you can smell ozone. The ozone itself is odorless. The smell arises because this intense radical easily combines or oxidizes with other substances in the air.

Fabricsmedium dielectric strength
air3.3 kV / mm
paper10 kV / mm
Cell membrane of a human nerve fiber14 kV / mm
porcelain20 kV / mm
PVC50 kV / mm
mica60 kV / mm
Polystyrene100 kV / mm

Influence (charge separation)


If you move a metallic object in an electric field, a charge separation occurs in this object. This means that an electrical voltage is created in it. This process is also called influenza. A charge-free zone is created in the middle of the object. If the object is separated in its middle, a field-free space is created. This creates the principle of shielding against electrical fields (Faraday cage).
The influence is only possible in conductor materials.

Shielding of unwanted electrical fields


Electric fields basically have the disadvantage of influencing the electronic circuit or circuit parts around them. Between two current-carrying conductors with different charges, the force of the electric field always results in charge separation (influence). The resulting tensions can have a disruptive effect. For example, through noise or hum in audio and video transmissions.
In order to avoid or reduce the influence, shielding by means of a ground connection is usually used. The electrical conductor is shielded by a metallic sheathing. By connecting the shell to the earth or mass, the electric field is canceled. The shielding is mostly realized by a metal housing or in cables by braiding or grids.
Electric fields are mainly generated by live parts and cables.

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