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Faraday's electromagnetic induction
August 1831· Invention or discovery· Tools, energy & materials
Well documentedSolid records, physical evidence or scientific consensus.
Michael Faraday discovered that a changing magnetic field creates an electric current, the principle behind generators and transformers.
See it on the Technology & Medicine map →How it works
After Ørsted showed in 1820 that current creates magnetism, Faraday sought the reverse. On August 29, 1831, he wound two coils on an iron ring: switching current on or off in one briefly produced current in the other. Weeks later he made current by moving a magnet through a coil, and built a spinning copper-disc generator. Faraday, a former bookbinder's apprentice with little schooling, explained it with invisible 'lines of force'.
Why it mattered
Nearly all electricity today is made by induction in generators and moved by transformers: the foundation of the electric grid.
How we know
Faraday's laboratory diary entry for August 29, 1831, his published Experimental Researches in Electricity, and the original induction ring, kept at the Royal Institution.
Still unknown or debated
American Joseph Henry may have observed induction first but published later; credit for the discovery is often shared.
Connections (3)
▸Faraday's electromagnetic induction made possible Electric power and the gridWell documented
The connection
Faraday found in 1831 that moving a magnet near a coil of wire creates a current. Every generator, from Gramme's 1871 dynamo to today's power plants, uses that principle: steam, water, wind or gas turbines spin magnets past coils. Transformers, which make long-distance lines practical, also run on induction.
When and how
Faraday at the Royal Institution in London, August 1831; Gramme's dynamo in Paris, 1871; Edison's power stations in London and New York, 1882.
How we know
Faraday's lab diary and 1831 paper describe his ring and disk experiments; the physics is the textbook basis of all generators and transformers.
Debates and open questions
Joseph Henry in the US found induction about the same time but published later; the 40-year gap to practical dynamos reflects engineering, not physics.
▸Faraday's electromagnetic induction lets coils read the signals of the MRI scannerWell documented
The connection
Faraday found in 1831 that a changing magnetic field makes current flow in a nearby wire. In an MRI scanner, hydrogen nuclei act like tiny spinning magnets; as they wobble after a radio pulse, their changing field induces a faint current in receiver coils. That current is the raw signal turned into images.
When and how
Faraday at the Royal Institution, London, August 1831; MRI's signal detection grew from 1946 nuclear magnetic resonance work by Felix Bloch at Stanford and Edward Purcell at Harvard.
How we know
MRI physics textbooks state the signal is picked up by electromagnetic induction in receiver coils, which is Faraday's law; the link is basic physics, not inference.
Debates and open questions
Not disputed. Engineering questions remain: stronger magnets give clearer signals, but very high-field scanners raise costs and safety questions.
▸Volta's electric battery made possible the experiments of Faraday's electromagnetic inductionMostly agreed
The connection
Before 1800, electricity came only as brief sparks from friction machines and Leyden jars. Volta's pile supplied steady current, which Ørsted found in 1820 deflects a compass needle. Faraday, using batteries to power his coils, showed in 1831 that the reverse also works: a changing magnetic field drives current in a nearby coil.
When and how
Pavia, Italy, 1800 (Volta); Copenhagen, 1820 (Ørsted); Royal Institution, London, August 29, 1831 (Faraday).
How sure are we?
Faraday's laboratory diary records the battery-powered iron-ring experiment; the original ring survives at the Royal Institution.
Debates and open questions
Faraday found the effect but explained it with 'lines of force' that mathematicians doubted; only Maxwell's equations of the 1860s gave it full theory.