= Faraday induction-ring experiment
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{title2=1831}
= Faraday induction ring
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<Michael Faraday>'s induction ring separates two questions: can one <electrical circuit> affect another without an electrical connection, and does that effect continue under steady conditions? The surviving apparatus uses insulated <copper> windings around an <iron> ring; the Royal Institution dates the successful experiment to 29 August 1831.<Michael Faraday's ring-coil apparatus by Royal Institution>[Collection record, date, materials and Description]{ref}
Faraday connected one winding group to a <battery>, the other to a <galvanometer>. Making battery contact deflected the needle; maintaining contact let it return to rest; breaking contact reversed the response. Reversing the battery reversed the deflections. His separate cylinder comparison enhanced induction with <iron>, whereas replacing it with <copper> gave no enhancement over the windings alone.<Experimental Researches in Electricity, Volume 1 by Michael Faraday>[First Series, §§27–30, ring, connections and reversal; §§34–35, distinct cylinder comparison]{ref}
\Image[/faraday-induction-ring-functional-apparatus.png]
{title=Separate electrical circuits in Faraday's induction-ring experiment}
{description=Original functional diagram. Each drawn winding represents a winding group; the illustration gives no historical turn count, dimensions or scale. The needle is the readout, rather than a plotted electric-current measurement.}
{source=faraday-induction-ring-functional-apparatus.py}
The contrast between a switching response and a quiet steady state makes <mutual induction> tangible. A steady primary <electric current> can maintain <magnetic flux> without sustaining a secondary <electromotive force>. Changes in <magnetic flux linkage> matter, as expressed by <Faraday's law of induction>. This is why a driven <electrical transformer> uses repeated changes in <magnetic flux> to supply secondary <power>.
The <galvanometer readout of an induction pulse> also separates the measured motion from the inferred <electric current>. Its <moment of inertia> and <damping> mean that a deflection is not an instantaneous trace of <electric current>. The following <coupled RL induction model> calculates currents in a stipulated circuit, rather than fitting Faraday's needle motion or reconstructing his switching times.
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