Oersteds

The oersted (symbol: Oe) is a unit of magnetic field strength used in the centimeter-gram-second (CGS) Gaussian and related CGS systems. It is named after the Danish physicist Hans Christian Ørsted, who demonstrated the link between electricity and magnetism. The oersted measures H, the magnetic field intensity, rather than B, the magnetic flux density.

In the CGS Gaussian system, B and H share the same dimensions in vacuum, so 1 oersted roughly corresponds to 1 gauss in terms of magnetic flux density. In practical terms, 1 Oe is equivalent to about 79.577 ampere-turns per meter (A/m) in SI units for H. The corresponding magnetic flux density in vacuum is about 1×10^-4 tesla (1 gauss). The distinction between H (in oersteds) and B (in gauss) can be subtle in CGS, especially inside materials where magnetization affects the relationship between the two.

Modern practice predominantly uses SI units, with B measured in teslas and H in amperes per meter. Consequently, the oersted has largely historical usage, appearing mainly in older literature or in discussions of CGS-era magnetism. Some CGS variants, such as CGS-emu and CGS-esu, have slightly different conventions, but the oersted remains the CGS unit historically associated with magnetic field strength.

In summary, the oersted is a CGS unit of magnetic field strength named after Ørsted, chiefly of historical importance, with 1 Oe ≈ 79.58 A/m for H and ≈ 1×10^-4 T for the corresponding B in vacuum.