Oersted
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
- Failed to parse (Conversion error. Server ("https://wikimedia.org/api/rest_") reported: "Cannot get mml. Server problem."): {\displaystyle B({\text{G}})=\mu _{\text{r}}H({\text{Oe}}).}
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]
- Failed to parse (Conversion error. Server ("https://wikimedia.org/api/rest_") reported: "Cannot get mml. Server problem."): {\displaystyle 1{\text{ Oe}}={\frac {1000}{4\pi }}~{\text{A}}/{\text{m}}.}
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.