# Field Intensity, Magnetic

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

## Field Intensity, Magnetic

a physical vector quantity (H) that is a quantitative characteristic of a magnetic field. The magnetic field intensity is independent of the magnetic properties of the medium and in free space is the same as the magnetic induction B; numerically, H = B in the centimeter-gram-second (cgs) system of units and H = B/μ0 in the International System of Units (SI), where μ0 is the magnetic constant. In a medium, the magnetic field intensity H determines the contribution to the magnetic induction B made by external field sources: H = B —4πJ (in the cgs system) or H = (B00) —J (in SI units), where J is the intensity of magnetization of the medium. If we introduce the relative magnetic permeability of the medium μ, then for an isotropic medium we have H = B/(μ0 μ) (in SI units). The units of magnetic field intensity in the SI system are amperes per meter (A/m); in the cgs system this unit is called an oersted; 1 A/m = 4π . 10-3 oersted ≃ 1.256 • 10-2 oersted.

The magnetic field intensity of a rectilinear conductor carrying a current I (in SI units) is H = μ0I/2πa, where a is the distance from the conductor. In the center of a ring current, H = μ0I/2R, where R is the radius of a loop carrying the current I. Along the axis of a solenoid, H = μ0ni, where n is the number of turns per unit length of the solenoid. The practical determination of H in ferromagnetic media (in magnetic materials) is based on the constancy of the tangential component of H during a transition from one medium to another. If the intensity of magnetization of a body is homogeneous, the field intensity measured on the parts of its surface that are parallel to the magnetization vector will correspond to the field intensity within the body.

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