Hopkinson's Law: The Magnetic Analogy To Ohm's Law
In electronic circuits, Ohm's law is an empirical relation between the EMF applied across an element and the current I it generates through that element. It is written as:
where R is the electrical resistance of that material. Hopkinson's law is a counterpart to Ohm's law used in magnetic circuits. The law is named after the British electrical engineer, John Hopkinson. It states that
where is the magnetomotive force (MMF) across a magnetic element, is the magnetic flux through the magnetic element, and is the magnetic reluctance of that element. (It shall be shown later that this relationship is due to the empirical relationship between the H-field and the magnetic field B, B=μH, where μ is the permeability of the material.) Like Ohm's law, Hopkinson's law can be interpreted either as an empirical equation that works for some materials, or it may serve as a definition of reluctance.
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