Maxwell (unit)

The maxwell (symbol: Mx) is the CGS (centimetre–gram–second) unit of magnetic flux (Φ).^[1]

maxwell
Unit system	Gaussian units
Unit of	magnetic flux
Symbol	Mx
Named after	James Clerk Maxwell
Derivation	1 G⋅cm2
Conversions
1 Mx in ...	... is equal to ...
Gaussian base units	1 cm3/2⋅g1/2⋅s−1
SI units	≘ 10−8 Wb

History

The unit name honours James Clerk Maxwell,^[2] who presented a unified theory of electromagnetism. The maxwell was recommended as a CGS unit at the International Electrical Congress held in 1900 at Paris.^[3] This practical unit was previously called a line,^[4] reflecting Faraday's conception of the magnetic field as curved lines of magnetic force,^[5] which he designated as line of magnetic induction.^[4] Kiloline (10³ line) and megaline (10⁶ line) were sometimes used because 1 line was very small relative to the phenomena that it was used to measure.^[5]

The maxwell was affirmed again unanimously as the unit name for magnetic flux at the Plenary Meeting of the International Electrotechnical Commission (IEC) in July 1930 at Oslo.^[6] In 1933, the Electric and Magnetic Magnitudes and Units committee of the IEC recommended to adopt the metre–kilogram–second (MKS) system (Giorgi system), and the name weber was proposed for the practical unit of magnetic flux (Φ), subject to approval of various national committees, which was achieved in 1935.^[7] The weber was thus adopted as a practical unit of magnetic flux by the IEC.

Definition

The maxwell is a non-SI unit.^[8]

1 maxwell = 1 gauss × (centimetre)²

That is, one maxwell is the total flux across a surface of one square centimetre perpendicular to a magnetic field of strength one gauss.

The weber is the related SI unit of magnetic flux, which was defined in 1946.^[9]

1 maxwell ≘ 10⁻⁴ tesla × (10⁻² metre)² = 10⁻⁸ weber

See also

• Centimetre–gram–second system of units
• Gaussian units
• Maxwell's equations

References

1. International Bureau of Weights and Measures (2006), The International System of Units (SI) (PDF) (8th ed.), ISBN 92-822-2213-6, archived (PDF) from the original on 2021-06-04, retrieved 2021-12-16, p. 128
2. "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." — Roche, John James; The Mathematics of Measurement: A Critical History, The Athlone Press, London, 1998, ISBN 0-485-11473-9, page 184 and Roche, John James; "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 Egidi, Claudio; 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
3. "Séance de clôture". Congrès international d'électricité (in French). Paris: Gauthier-Villars. 1901. p. 354.
4. Gyllenbok, Jan (2018). "line". Encyclopaedia of Historical Metrology, Weights, and Measures, Volume 1. Birkhäuser. p. 141. ISBN 9783319575988. Retrieved 20 April 2018.
5. Klein, Herbert Arthur (1988) [1974]. The science of measurement: A historical survey. Dover. p. 481.
6. Kennelly, Arthur E. (1933). "Conference of the Symbols, Units and Nomenclature (S. U. N.) Commission of the International Union of Pure and Applied Physics (I. P. U.), at Paris, in July, 1932, and its Results". Proceedings of the National Academy of Sciences of the United States of America. 19 (1): 146. Bibcode:1933PNAS...19..144K. doi:10.1073/pnas.19.1.144. JSTOR 85786. PMC 1085894. PMID 16587728.
7. Kennelly, Arthur E. (1935). "I.E.C. adopts MKS system of units". Electrical Engineering. 54 (12): 1377. doi:10.1109/EE.1935.6538821. S2CID 51664669.
8. "Non-SI units accepted for use with the SI, and units based on fundamental constants (contd.)". SI Brochure: The International System of Units (SI) [8th edition, 2006; updated in 2014]. Bureau international des poids et mesures. Archived from the original on 2019-06-08. Retrieved 19 April 2018.
9. International Bureau of Weights and Measures (2006), The International System of Units (SI) (PDF) (8th ed.), ISBN 92-822-2213-6, archived (PDF) from the original on 2021-06-04, retrieved 2021-12-16, p. 144