Magnetomotive force
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In physics, the magnetomotive force is a quantity appearing in the equation for the magnetic flux in a magnetic circuit, often called Ohm's law for magnetic circuits.[1] It is the property of certain substances or phenomena that give rise to magnetic fields:
where Φ is the magnetic flux and R is the reluctance of the circuit. It can be seen that the magnetomotive force plays a role in this equation analogous to the voltage V in Ohm's law: V = IR, since it is the cause of magnetic flux in a magnetic circuit:[2]
- ℱ = NI
- where N is the number of turns in the coil and I is the electric current through the circuit. Sometimes the unit of gilbert is used to express ℱ.
- ℱ = ΦR
- where Φ is the magnetic flux and R is the magnetic reluctance
- ℱ = HL
- where H is the magnetizing force (the strength of the magnetizing field) and L is the mean length of a solenoid or the circumference of a toroid
History
The term magnetomotive force was coined by Henry Augustus Rowland in 1880. Rowland intended this to indicate a direct analogy with electromotive force.[3] The idea of a magnetic analogy to electromotive force can be found much earlier in the work of Michael Faraday (1791-1867) and it is hinted at by James Clerk Maxwell (1831-1879). However, Rowland coined the term and was the first to make explicit an Ohm's law for magnetic circuits in 1873.[4]
Ohm's law for magnetic circuits is sometimes referred to as Hopkinson's law rather than Rowland's law as some authors attribute the law to John Hopkinson instead of Rowland.[5] According to a review of magnetic circuit analysis methods this is an incorrect attribution originating from an 1885 paper by Hopkinson.[6] Furthermore, Hopkinson actually cites Rowland's 1873 paper in this work.[7]
References
Bibliography
Cited sources
- Hon, Giora; Goldstein, Bernard R, "Symmetry and asymmetry in electrodynamics from Rowland to Einstein", Studies in History and Philosophy of Modern Physics, vol. 37, iss. 4, pp. 635-660, Elsevier December 2006.
- Hopkinson, John, "Magnetisation of iron", Philosophical Transactions of the Royal Society, vol. 176, pp. 455-469, 1885.
- Lambert, Mathieu; Mahseredjian, Jean; Martínez-Duró, Manuel; Sirois, Frédéric, "Magnetic circuits within electric circuits: critical review of existing methods and new mutator implementations", IEEE Transactions on Power Delivery, vol. 30, iss. 6, pp. 2427-2434, December 2015.
- Rowland, Henry A, "On magnetic permeability and the maximum magnetism of iron, steel, and nickel", Philosophical Magazine, series 4, vol. 46, no. 304, pp. 140-159, August 1873.
- Rowland, Henry A, "On the general equations of electro-magnetic action, with application to a new theory of magnetic attractions, and to the theory of the magnetic rotation of the plane of polarization of light" (part 2), American Journal of Mathematics, vol. 3, nos. 1-2, pp. 89–113, March 1880.
- Schmidt, Robert Munnig; Schitter, Georg, "Electromechanical actuators", ch. 5 in Schmidt, Robert Munnig; Schitter, Georg; Rankers, Adrian; van Eijk, Jan, The Design of High Performance Mechatronics, IOS Press, 2014 ISBN 1614993688.
- Thompson, Silvanus Phillips, The Electromagnet and Electromagnetic Mechanism, Cambridge University Press, 2011 (first published 1891) ISBN 1108029213.
- Smith, R.J. (1966), Circuits, Devices and Systems, Chapter 15, Wiley International Edition, New York. Library of Congress Catalog Card No. 66-17612
- Waygood, Adrian, An Introduction to Electrical Science, Routledge, 2013 ISBN 1135071136.
General references
- The Penguin Dictionary of Physics, 1977, ISBN 0-14-051071-0
- A Textbook of Electrical Technology, 2008, ISBN 81-219-2440-5