Electric and magnetic fields

Electric field caused by electric charges: The arrows indicate the field lines.

When current flows, electrical appliances and wires generate two types of fields: electric and magnetic fields. An electric field is produced as soon as voltage is applied to an appliance or wire. Voltage is the prerequisite that enables current to flow when an appliance is switched on. When current flows, a magnetic field is produced in addition to the electric field. Thus, electrical appliances and wires, with current flowing through them, are surrounded by electric and magnetic fields.

Low-frequency electric and magnetic fields

Alternating current (AC) is mostly used for power supply. In Germany, AC has a frequency of 50 hertz (Hz). This means that the current alternates direction 100 times per second. The electric and magnetic fields change direction just as often as the current. The frequency of 50 Hertz lies in the lower range of the electromagnetic spectrum. Therefore, these fields are called "low-frequency."

Magnetic field caused by current: Blue arrows indicate the direction of the electric current. Red arrows indicate the magnetic field lines.

Field strengths and units of measurement

The strength of an electric field increases with the voltage applied to the wire. The unit of measurement for voltage is the volt (V). The electric field strength is expressed in volts per metre (V/m).

The strength of the magnetic field around an electrical line depends on the electric current that flows. The current is measured in amperes (A), and the magnetic field strength is measured in amperes per meter (A/m).

Magnetic flux density is relevant for radiation protection. The generation of electrical currents in conductive bodies is directly related to this quantity. It is mathematically linked to the magnetic field strength.The unit of measurement is tesla (T) or microtesla (µT). One microtesla is one-millionth of a tesla (0.000001 T).

Electric and magnetic fields in everyday life

The electric field strengths and magnetic flux densities are generally low at the usual working distance from electrical household appliances and electrical household wiring.

For some appliances higher magnetic flux densities are possible, however, in most cases only very close to the surface of the devices (for example appliances with high power consumption such as vacuum cleaners or hair dryers). The further you move away, the weaker the electric and magnetic fields become.

The exposure of the population to low-frequency fields is, therefore, usually low. This also applies to people living near high-voltage lines.

Distance and Shielding

In principle field strength decreases with increasing distance from the field source. Additionally electric fields are shielded, for example, by common building materials. By contrast, a relatively elaborate shielding is required for magnetic fields.