Electromagnetic Field

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Electromagnetic field

A changing magnetic field always produces an electric field, and conversely, a changing electric field always produces a magnetic field. This interaction of electric and magnetic forces gives rise to a condition in space known as an electromagnetic field. The characteristics of an electromagnetic field are expressed mathematically by Maxwell's equation. See Electric field, Electromagnetic radiation, Electromagnetic wave

McGraw-Hill Concise Encyclopedia of Physics. © 2002 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Electromagnetic Field

a special form of matter that mediates the interaction between charged particles (seeFIELD).

In a vacuum, an electromagnetic field is characterized by the electric field strength E and the magnetic flux density B, which determine the forces exerted by the field on stationary or moving charged particles. In addition to the vectors E and B, which are measured directly, an electromagnetic field may be characterized by a scalar potential φ and a vector potential A. The potentials are not uniquely determined, a gauge transformation being required.

In a medium, an electromagnetic field is also characterized by the following two auxiliary vector quantities: the magnetic field strength H and the electric flux density D (seeINDUCTION, ELECTRICAL AND MAGNETIC).

The behavior of electromagnetic fields is a subject of classical electrodynamics. In an arbitrary medium, the behavior of such fields is described by Maxwell’s equations. The equations make it possible to determine the fields as a function of the distributions of charge and current.

Microscopic electromagnetic fields, which are produced by individual elementary particles, are characterized by the strengths of the microscopic electric field (e) and the microscopic magnetic field (h). The mean values of the microscopic field strengths are related to the macroscopic characteristics of an electromagnetic field in the following way: ē = E and h̄ = B. Microscopic fields satisfy the Lorentz-Maxwell equations.

The electromagnetic field of stationary charged particles or of charged particles moving with constant velocity is inseparably bound to the particles. When particles are accelerated, their electromagnetic field is “torn away” and exists independently in the form of electromagnetic waves.

The generation of an electromagnetic field by an alternating magnetic field and the generation of a magnetic field by an AC electric field show that alternating electric and magnetic fields do not exist separately, that is, are not independent of one another. According to the theory of relativity, the components of the vectors that characterize an electromagnetic field form a single physical quantity called the electromagnetic field tensor. The components of the tensor are transformed upon a transition from one inertial reference frame to another, in accordance with the Lorentz transformations.

At high field frequencies, the quantum properties of an electromagnetic field become important. In this case, classical electrodynamics is not applicable and an electromagnetic field is described by quantum electrodynamics.

REFERENCES

Tamm, I. E. Osnovy teorii elektrichestva, 9th ed. Moscow, 1976.
Kalashnikov, S. G. Elektrichestvo, 4th ed. Moscow, 1977. (Obshchii kurs fiziki, vol. 2.)
Feynman, R., R. Leighton, and M. Sands. Feinmanovskie leklsii po fizike, vols. 5–7. Moscow, 1966–67.
Landau, L. D., and E. M. Lifshits. Teoriia polia, 6th ed. Moscow, 1973. (Teoreticheskaia fizika, vol. 2.)
Landau, L. D., and E. M. Lifshits. Elektrodinamika sploshnykh sred. Moscow, 1959.

G. IA. MIAKISHEV

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

electromagnetic field

[i¦lek·trō·mag′ned·ik ′fēld]
(electromagnetism)
An electric or magnetic field, or a combination of the two, as in an electromagnetic wave.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
That power is lost to the EM field (the opposite of what happened before).
McFadden views the brain's electromagnetic field as arising from the induced EM field of neurons.
The frequency dependence of a response function for a given observation site can be estimated through spectrum analysis (7) of obtained time series data for the EM field components.
Application of the SPM method on (3) and (4) above leads to the following analytic expressions for the EM field in the higher half space (x > 0) [10], [11]
When it comes to estimating the performances of such a detector, for recovering 10% of the original EM field created by a neutrino interaction in a medium where the sedimentary layers have at least 9 cm thickness, the distance from the interaction point to detecting antenna should be less than 100 m.
In a side-channel attack on a contactless smart card, the data-and operation-dependent power consumption is generally measured indirectly via the EM field of the target device by using an EM probe [3,4].
Hence, the intensified EM field around Au NRs would increase the absorption of the photoactive film near the plasmon peaks of the rods, in which an enhancement in the film absorption near the IR region is expected [14,18].
This is because, unlike the conventional ADI-FDTD method, the leapfrog ADI-FDTD method has only one-step and with no mid-time EM fields needed to be stored.
Maurice, "Prediction of the field radiated at one meter from PCB's and microprocessors from near EM field cartography," Proc.
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First, the theory predicts that medically relevant information is available in the EM field of the body as a whole, not just the brain and heart fields.

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