The oersted (, symbol Oe) is the coherent derived unit of the auxiliary magnetic field H in the CGS-EMU and Gaussian systems of units. It is equivalent to 1 dyne per maxwell.
In the Gaussian system, the unit of the H-field is the oersted and the unit of the B-field is the gauss. In the SI, the unit ampere per metre (A/m), which is equivalent to newton per weber, is used for the H-field and the unit tesla is used for the B-field.
The unit was established by the IEC in the 1930s in honour of Danish physicist Hans Christian ÃÂrsted. ÃÂrsted 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.
The oersted is defined as a dyne per unit pole. The oersted corresponds to (âÂÂ) amperes per metre, in terms of SI units.
The H-field strength inside a long solenoid wound with 79.58 turns per metre 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, and has exactly turns per metre.
The oersted is closely related to the gauss (G), the CGS unit of magnetic flux density. In 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:
The stored energy in a magnet, called magnet performance or maximum energy product (often abbreviated BH<sub>max</sub>), is typically measured in units of megagauss-oersteds (MGâ Oe).