![]() Hopkinson, John, "Magnetisation of iron", Philosophical Transactions of the Royal Society, vol.Hon, Giora Goldstein, Bernard R, "Symmetry and asymmetry in electrodynamics from Rowland to Einstein", Studies in History and Philosophy of Modern Physics, vol. ![]() Furthermore, Hopkinson actually cites Rowland's 1873 paper in this work. According to a review of magnetic circuit analysis methods this is an incorrect attribution originating from an 1885 paper by Hopkinson. ![]() 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. However, Rowland coined the term and was the first to make explicit an Ohm's law for magnetic circuits in 1873. 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). Rowland intended this to indicate a direct analogy with electromotive force. The term magnetomotive force was coined by Henry Augustus Rowland in 1880. Occasionally, the cgs system unit of the gilbert may also be encountered. This was the unit name in the MKS system. Informally, and frequently, this unit is stated as the ampere-turn to avoid confusion with current. The SI unit of mmf is the ampere, the same as the unit of current (analogously the units of emf and voltage are both the volt). 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.
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