The oersted (symbol Oe) is the
coherent derived unit of the
auxiliary magnetic field H in the
centimetre–gram–second system of units
The centimetre–gram–second system of units (abbreviated CGS or cgs) is a variant of the metric system based on the centimetre as the unit of length, the gram as the unit of mass, and the second as the unit of time. All CGS mechanical units ...
(CGS). It is equivalent to 1
dyne per
maxwell
Maxwell may refer to:
People
* Maxwell (surname), including a list of people and fictional characters with the name
** James Clerk Maxwell, mathematician and physicist
* Justice Maxwell (disambiguation)
* Maxwell baronets, in the Baronetage of ...
.
Difference between CGS and SI systems
In the CGS system, the unit of the
H-field
A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...
is the oersted and the unit of the
B-field
A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...
is the
gauss. In the SI system, the unit ampere per meter (A/m), which is equivalent to
newton per
weber
Weber (, or ; German: ) is a surname of German origin, derived from the noun meaning " weaver". In some cases, following migration to English-speaking countries, it has been anglicised to the English surname 'Webber' or even 'Weaver'.
Notable pe ...
, is used for the H-field and the unit of
tesla is used for the B-field.
History
The unit was established by the
IEC
The International Electrotechnical Commission (IEC; in French: ''Commission électrotechnique internationale'') is an international standards organization that prepares and publishes international standards for all electrical, electronic and r ...
in the 1930s in honour of Danish physicist
Hans Christian Ørsted
Hans Christian Ørsted ( , ; often rendered Oersted in English; 14 August 17779 March 1851) was a Danish physicist and chemist who discovered that electric currents create magnetic fields, which was the first connection found between electricit ...
. Ørsted discovered the connection between magnetism and electric current when a magnetic field produced by a current-carrying copper bar deflected a magnetised needle during a lecture demonstration.
Definition
The oersted is defined as a
dyne per
unit pole. The oersted is (≈) amperes per meter, in terms of
SI units
The International System of Units, known by the international abbreviation SI in all languages and sometimes pleonastically as the SI system, is the modern form of the metric system and the world's most widely used system of measurement. ...
.
The H-field strength inside a long
solenoid
upright=1.20, An illustration of a solenoid
upright=1.20, Magnetic field created by a seven-loop solenoid (cross-sectional view) described using field lines
A solenoid () is a type of electromagnet formed by a helix, helical coil of wire whose ...
wound with 79.58 turns per meter of a wire carrying 1
A is approximately 1 oersted. The preceding statement is exactly correct if the solenoid considered is infinite in length with the current evenly distributed over its surface.
The oersted is closely related to the gauss (G), the CGS unit of magnetic flux density. In a vacuum, if the magnetizing field strength is 1 Oe, then the magnetic field density is 1 G, whereas, in a medium having
permeability (relative to permeability of vacuum), their relation is:
:
Because oersteds are used to measure magnetizing field strength, they are also related to the
magnetomotive force (mmf) of current in a single-winding wire-loop:
:
Stored energy
The stored energy in a magnet, called ''magnet performance'' or ''maximum energy product''
(often abbreviated BH
max), is typically measured in units of megagauss-oersteds (MG⋅Oe).
See also
*
Centimetre–gram–second system of units
The centimetre–gram–second system of units (abbreviated CGS or cgs) is a variant of the metric system based on the centimetre as the unit of length, the gram as the unit of mass, and the second as the unit of time. All CGS mechanical units ...
*
Ampere's model of magnetization
References
{{CGS units
Centimetre–gram–second system of units
Units of magnetic induction