In Plain Terms
Bring a magnet close to a coil of copper wire, then move it away: during the movement, and only during the movement, an electric current flows through the wire. That is what Michael Faraday established on August 29, 1831, and it is the principle that produces virtually all of the world's electricity today. A magnet at rest produces nothing: something has to change for a current to appear. That is why a generator has to keep turning, and why a transformer only works on alternating current. Faraday did not write the equation: he demonstrated the phenomenon, and Maxwell put it into a formula some thirty years later.
Discovery — Electromagnetic Induction (1831)
| Parameter | Value |
|---|---|
| Date | August 29, 1831 |
| Location | Royal Institution, London |
| Discoverer | Michael Faraday, self-taught British chemist and physicist (former bookbinder's apprentice) |
| Prior art | Ørsted, 1820: an electric current creates a magnetic field |
| Prior research | 10 years of attempts to produce electricity from magnetism |
| Apparatus | Iron ring wound with two copper coils |
| Observation | Transient current when the battery is connected/disconnected |
| Law formulated | EMF = −dΦ/dt (rate of change of magnetic flux) |
| Key innovation | Only a changing field (not a static one) produces current |
The Three Experiments of 1831
| Date | Apparatus | Observed result |
|---|---|---|
| August 29, 1831 | Soft iron ring carrying two copper coils, connected to a battery | Brief galvanometer deflection on connection, deflection in the opposite direction on disconnection |
| October 17, 1831 | Magnet pushed into and then pulled out of a copper coil | Current on insertion, reversed current on withdrawal; the faster the motion, the stronger the current |
| October 28, 1831 | Copper disk spinning between the poles of a magnet | Continuous current — the first electric generator in history |
Technical Explanation — Faraday's Law
Before Faraday, Ørsted (1820) had shown that a steady current deflects a magnetized needle (electricity produces magnetism). The symmetrical question — can magnetism produce electricity? — seemed impossible, because a static magnet does nothing.
1. Faraday's ring (August 29, 1831) — Faraday wound two copper coils around a soft iron ring. When he connected a battery to the first coil, the galvanometer on the second deflected briefly. When he disconnected it, the galvanometer deflected in the opposite direction. Current appeared only during the change in the field.
2. The magnet and the coil (October 17, 1831) — Faraday pushed a magnet into a copper coil: current. He pulled it out: reversed current. The faster the motion, the stronger the current. This was the visual demonstration of induction.
3. The Faraday disk (October 28, 1831) — Faraday spun a copper disk between the poles of a magnet: the first continuous electric generator in history. Mechanical motion was converted into electric current on a permanent basis. The power delivered was minute — an order of a few milliwatts is sometimes quoted, a figure none of the sources listed below supports — but the principle itself was established.
4. The mathematical formulation — James Clerk Maxwell would later formalize Faraday's law: ε=−dtdΦB. The induced electromotive force is proportional to the rate of change of the magnetic flux. The negative sign (Lenz's law) indicates that the induced current opposes the change that creates it. Faraday himself, self-taught, is said to have been unfamiliar with differential calculus: he reasoned through physical images — his lines of force, which he pictured filling the space around magnets — rather than through equations. It was Maxwell who turned that geometric intuition into mathematical theory.
Why It Worked
The fundamental principle is that only the time variation of magnetic flux creates an electromotive force. A static magnet produces nothing. That is why generators must turn continuously, and why transformers only work on alternating current (continuous variation). Faraday intuitively grasped what Maxwell would formalize 30 years later in his equations.
Causal Chain
Faraday's induction (1831) → Gramme dynamo (1871) → Electric lighting (Edison, 1879) → Power stations → Alternating current (Tesla, 1888) → Global electrification → Electronics → Digital society
Anecdote
Faraday, the son of a blacksmith, declined the title of knight and the presidency of the Royal Society. He died in 1867 in a house given to him by Queen Victoria. Einstein would keep a portrait of Faraday in his office — next to Newton and Maxwell.
A frequently repeated but never attested anecdote has it that a minister — the Chancellor of the Exchequer William Gladstone, so the story goes — asked Faraday what use electricity could possibly be, and that Faraday replied: “One day, sir, you may tax it.” No contemporary source documents the exchange: it is a line attributed after the fact, to be taken as such and not as a historical event.
Legacy and Current Data
Faraday's law governs virtually all of the world's electricity generation. Apart from photovoltaics (photoelectric effect) and fuel cells (electrochemistry), all electricity passes through a generator based on Faraday's induction.
Induction is not confined to power generation: nearly two centuries later, it has passed into everyday objects. Qi-standard wireless charging transfers energy between two coils without contact. Induction hobs heat the ferromagnetic base of a pan by eddy currents. Magnetic resonance imaging (MRI) picks up, in receiver coils, the signal induced by the precession of spins. Regenerative braking in electric and hybrid vehicles runs the motor as a generator and returns part of the kinetic energy to the battery. All of these are direct applications of the principle established in 1831.
Sources
References verified during the fact-checking audit of August 2026: these are the pages
against which this bulletin's claims were checked.