| oersted | |
|---|---|
| Unit system | Gaussian units |
| Unit of | magnetic field strength |
| Symbol | Oe |
| Named after | Hans Christian Ørsted |
| Derivation | 1 dyn/Mx |
| Conversions | |
| 1 Oe in ... | ... is equal to ... |
| Gaussian base units | 1 cm−1/2⋅g1/2⋅s−1 |
| SI units | (4π)−1×103 A/m ≈ 79.57747 A/m |
The oersted (/ˈɜːrstɛd/,[1] symbol Oe) is the coherent derived unit of the auxiliary magnetic field H in the CGS-EMU and Gaussian systems of units.[2] It is equivalent to 1 dyne per maxwell.
Difference between Gaussian and SI systems
[edit]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.[3]
History
[edit]The unit was established by the IEC in the 1930s[4] in honour of Danish physicist Hans Christian Ørsted. 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.[5]
Definition
[edit]
The oersted is defined as a dyne per unit pole.[clarification needed][6] The oersted corresponds to 1000/4π (≈79.5775) amperes per metre, in terms of SI units.[7][8][9][10]
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 1000/4π 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 μr (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:[11]
Stored energy
[edit]The stored energy in a magnet, called magnet performance or maximum energy product[12] (often abbreviated BHmax), is typically measured in units of megagauss-oersteds (MG⋅Oe).
See also
[edit]
References
[edit]- ^ "Oersted". Random House Webster's Unabridged Dictionary.
- ^ "as late as 1936 a subcommittee of the IEC International Electrotechnical Commission proposed the names 'maxwell', 'gauss' and 'oersted' for the cgs electromagnetic units of flux, induction and magnetic field strength, respectively". — John James Roche, The Mathematics of Measurement: A Critical History, The Athlone Press, London, 1998, ISBN 0-485-11473-9, page 184 and John James Roche, "B and H, the intensity vectors of magnetism: A new approach to resolving a century-old controversy", American Journal of Physics, vol. 68, no. 5, 2000, doi: 10.1119/1.19459, p. 438; in both cases giving the reference as Claudio Egidi, editor, Giovanni Giorgi and his Contribution to Electrical Metrology: Proceedings of the meeting held in Turin (Italy) on 21 and 22, September 1988, Politecnico di Torino, Turin (IT), 1990, ISBN 978-8885259003, pp. 53–56
- ^ Kaye, G. W. C, & Laby, T. H.: Table of Physical and Chemical Constants, page 14. Longman, 1973.
- ^ "IEC history". Archived from the original on 2019-05-21. Retrieved 2006-03-25.
- ^ "Hans Christian Oersted". Famous Scientists. Retrieved 2020-03-31.
- ^ Hirst, A. W. Electricity and Magnetism For Engineering Students. Blackie & Son Limited, 1959, p. 411.
- ^ "Magnetic Conversion Factors". Archived from the original on 2020-09-27. Retrieved 2008-03-11.
- ^ "EMF Fundamentals". Archived from the original on 2008-04-07.
- ^ "Oersted". Everything2.
- ^ "Derived CGS Units with Special Names". Surface Engineering Forum. Gordon England.
- ^ "Table 9. Non-SI units associated with the CGS and the CGS-Gaussian system of units". SI Brochure: The International System of Units (SI) [8th edition, 2006; updated in 2014]. BIPM. 2006.
- ^ "What is Maximum Energy Product / BHmax and How Does It Correspond to Magnet Grade?". Dura Magnetics USA. 15 September 2014. Retrieved 2020-01-20.