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Static Fields

1. What are static electric and magnetic fields?

    The source document for this Digest states:

    When a voltage is applied to an object such as an electrical conductor, the conductor becomes charged and forces start to act on other charges in the vicinity. Two types of forces may be distinguished: that which arises from stationary electric charges , known as the electrostatic force, and that which appears only when charges are moving (as in an electric current in a conductor), known as the magnetic force. The concept of field has been created to describe the existence and spatial distribution of these forces. Reference is then made to field of force, or simply electric and magnetic fields.

    The term static refers to a situation where all charges are fixed in space, or move as a steady flow, so that both charges and current densities are constant in time. For fixed charges there is an electric field whose strength at any point in space depends on the value and geometry of all the charges. For a steady current in a circuit, both the electric and magnetic field are constant in time (static fields), since the charge density at any point of the circuit is constant.

    Static electric and magnetic fields are characterized by steady, time independent strengths and correspond to the zero-frequency limit of the extremely low frequency (ELF) band. Electricity and magnetism are distinct phenomena as long as charges and current are static (ICNIRP, 1996).

    Source & ©: WHO "Environmental Health Criteria 232: Static Fields" (2006)
     Chapter 2 Physical Characteristics

    (See also the introduction of our Digest on Power lines.)

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