Electromagnetic induction
Faraday records successful electromagnetic induction with his ring coil
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Original prompt & settings (JSON) ↗Nothing happened continuously. The needle jumped at the instant the battery circuit changed — which was the discovery.
29 August 1831: a ring in a basement
In the basement laboratory of the Royal Institution in London, Michael Faraday spent 29 August 1831 testing a soft-iron ring — six inches across, seven-eighths of an inch thick — wound with electrically separate coils on opposite sides, labelled in his diary simply A and B.
He connected one side to a battery of ten paired plates and ran the other circuit past a magnetic needle placed three feet from the ring, far enough that the battery's own magnetic influence could not masquerade as induction. The needle deflected immediately when the battery circuit was made.
The effect was in the change
The induced effect was momentary rather than a sustained current: the secondary circuit responded when current in the primary circuit changed. Faraday recorded the successful experiment in his laboratory diary that day, listing wire lengths and plate sizes like a recipe.
The detector he describes is a magnetic needle in the secondary circuit — not the galvanometer of many retellings.
Not the Royal Society, not yet
This was an experiment at the Royal Institution, whose collection still holds the original ring-coil apparatus, wound with materials as ordinary as bonnet wire, cotton, twine and calico. Faraday gave no demonstration to the Royal Society that day.
His paper reporting the induction research was written later and read to the Royal Society on 24 November 1831 — which is where his priority for the first reported mutual induction rests, alongside Joseph Henry's independent work and Henry's priority for self-induction.
Sources
Researched 23 Aug 2026 6 sources 3 audit passes
How this was checked
Researched from the web into a fact sheet, rewritten from that sheet, then audited against it by a different model. How the pipeline works →
What the sources leave uncertain
- Joseph Henry began related work around August 1831, but the Smithsonian says delays prevented sustained investigation until June 1832 and that Faraday was first to report mutual induction. Henry's independent contribution and his priority for self-induction should not be collapsed into a claim of a simultaneous August 29 demonstration.
- The contemporary experiment registered a needle deflection. Explaining it today as induction from changing magnetic flux is correct modern physics, but Faraday did not yet express the result in that later mathematical language.