Faraday's Induction: From Magnets to Electricity

In 1831, Michael Faraday — a self-educated scientist who began his career as a bookbinder's apprentice — conducted an experiment that would electrify the world. He discovered that moving a magnet near a wire creates an electric current.

This discovery of electromagnetic induction, made with a handful of wire, a cardboard tube, and a galvanometer, launched the electrical age and remains one of the most consequential scientific findings in history. Without it, there are no generators, no electric motors, no power grid, and no modern civilization as we know it.

The Electrical World Before Faraday

To appreciate Faraday's achievement, it helps to understand the state of electricity and magnetism in 1831.

Electricity as a practical phenomenon had been known for roughly a century. Alessandro Volta had invented the battery in 1800, producing the first reliable source of continuous electric current — before Volta, electricity meant the static discharge from Leyden jars. The battery enabled chemists like Humphry Davy to use electric current to decompose compounds (electrolysis), discovering several new elements including sodium and potassium.

In 1820, Danish physicist Hans Christian Oersted made a striking observation: a compass needle deflected when placed near a wire carrying electric current. Current creates magnetism. This was the first direct evidence that electricity and magnetism were related forces — until then, they had been studied as entirely separate phenomena.

André-Marie Ampère quickly formalized Oersted's observation mathematically, showing that current-carrying wires attract or repel each other like magnets, and that the magnetic force around a wire follows quantifiable rules.

But the relationship seemed one-directional. Current makes magnetism — but does magnetism make current? Several researchers, including Faraday himself, had been trying to answer this question for years.

Faraday's Background: The Autodidact

Michael Faraday's story is as extraordinary as his discoveries. Born in 1791 in south London to a blacksmith, he received little formal education. At 14, he became an apprentice to a bookbinder, and spent his evenings reading the books he was binding — including scientific texts and an article on electricity in the Encyclopaedia Britannica.

In 1812, a customer gave Faraday tickets to a lecture series by Humphry Davy at the Royal Institution. Faraday was 21, with no scientific training and no formal education beyond elementary school. He took meticulous notes, bound them beautifully, and sent them to Davy with a request for a job. Davy hired him as a laboratory assistant in 1813.

Faraday spent the next two decades at the Royal Institution, gradually moving from assistant to the Institution's star scientist. He had no mathematics beyond basic arithmetic — he could not read the mathematical papers of Ampère or Maxwell. His genius was experimental and conceptual: an extraordinary intuition for physical processes and an unmatched ability to design experiments that tested ideas cleanly.

In 1820, he heard about Oersted's discovery and immediately began trying to find the reverse: could a magnet create electricity? For eleven years, he tried various approaches and failed.

The Discovery: August 29, 1831

The breakthrough came when Faraday changed his approach. Previous attempts had used static magnetic fields — a magnet held in place near a wire. What if the key was change?

Faraday wound wire coils around both sides of an iron ring (a toroidal core). One coil was connected to a battery; the other to a galvanometer (a sensitive instrument for detecting current). When he closed the circuit (allowing current to flow through the first coil), the galvanometer briefly deflected. When he opened the circuit (stopping the current), it deflected in the opposite direction. But when the current was steady — flowing but not changing — the galvanometer showed nothing.

A changing current in one coil was inducing a current in the other coil, through the iron ring.

This was electromagnetic induction, but mediated by mutual inductance — the changing magnetic field of one coil inducing current in another. Faraday went further. He wrapped wire around a cardboard tube and moved a bar magnet in and out of the tube while watching the galvanometer:

• Move the magnet into the coil → galvanometer deflects one way
• Hold the magnet still inside the coil → galvanometer reads zero
• Move the magnet out of the coil → galvanometer deflects the other way

A moving magnet created electricity. A stationary magnet, no matter how strong, created nothing.

The key was not magnetism per se, but changing magnetism. A changing magnetic field induces an electric field — and if that changing field passes through a conductor, it drives current.

Faraday's Law

Faraday formalized his observations into what became Faraday's Law of Induction: the induced electromotive force (voltage) in any closed circuit is equal to the negative rate of change of magnetic flux through the circuit.

In mathematical terms (formalized by Maxwell later): ε = −dΦ/dt

Where:

• ε is the induced voltage
• Φ (phi) is the magnetic flux — essentially the total magnetic field passing through the loop
• dΦ/dt is the rate of change of that flux

The negative sign indicates Lenz's Law: the induced current always flows in a direction that opposes the change that created it. Move a magnet toward a coil and the current induced in the coil creates a magnetic field that repels the incoming magnet. This is not just a mathematical convenience — it is a consequence of energy conservation. If the induced current aided the motion that created it, you could generate increasing energy from nothing.

How Generators Work

A generator is Faraday's experiment scaled up and made continuous. A coil of wire rotates inside a magnetic field (or a magnet rotates inside a coil). As it rotates, the angle between the coil and the magnetic field continuously changes — which means the magnetic flux through the coil continuously changes — which means, by Faraday's Law, a continuous voltage is induced in the coil.

The rotating coil continuously alternates between increasing and decreasing flux, producing an alternating current (AC) — the kind delivered to homes and factories. The mechanical energy of rotation is converted to electrical energy.

Every power plant in the world — whether coal-fired, natural gas, hydroelectric, nuclear, or wind — uses this same principle. The primary difference between them is the energy source used to rotate the generator:

• Coal/gas: Steam from combustion spins turbines
• Hydroelectric: Falling water spins turbines directly
• Nuclear: Steam from reactor heat spins turbines
• Wind: Wind spins turbine blades directly

All of them are rotating magnets in coils of wire, generating electricity through electromagnetic induction discovered in 1831.

How Electric Motors Work

A motor is the reverse of a generator. Instead of mechanical rotation producing electrical current, electrical current in a magnetic field produces mechanical rotation.

When current flows through a wire in a magnetic field, the wire experiences a force (this follows from Ampère's work — current creates magnetism, and magnetic fields exert forces on other magnets). In a motor, this force causes a rotor (rotating component) to turn. The mechanical energy of rotation can then drive pumps, fans, vehicles, conveyor belts, and everything else that moves in modern civilization.

Electric motors consume approximately 45% of the world's electricity. Every fan, elevator, electric vehicle, factory machine, and refrigerator compressor is an electric motor at its core — all fundamentally dependent on the relationship Faraday established between electricity and magnetism.

The Concept of Fields

Perhaps Faraday's deepest contribution was conceptual rather than experimental. He introduced the idea of fields to physics.

Before Faraday, forces were thought of as acting at a distance — a magnet attracted iron from across a room through some mysterious action, with nothing in between. Newton's gravity had the same character: mass attracted mass through empty space without any mediating mechanism.

Faraday was uncomfortable with this. He proposed that a magnet modifies the space around it, creating a magnetic field. This field is real — it exists even in the absence of other objects to feel its influence. Lines of magnetic force (now called field lines) filled space around magnets and currents in Faraday's mental model.

When Faraday said a changing magnetic field induces an electric field, he was making a profound statement: the two fields are coupled. A change in one creates the other.

James Clerk Maxwell, the 19th century's greatest mathematical physicist, took Faraday's experimental insights and field concepts and formalized them into Maxwell's Equations — four differential equations that describe all electromagnetic phenomena. These equations revealed something astonishing: a changing electric field also creates a changing magnetic field, which creates a changing electric field, and so on — a self-sustaining wave propagating through space at a speed Maxwell calculated to be approximately 3 × 10⁸ m/s.

This was the speed of light. Light is an electromagnetic wave — a traveling oscillation of electric and magnetic fields. Maxwell's unification of electricity, magnetism, and optics is one of the greatest achievements in the history of physics.

It all grew from Faraday's experiment with a wire, a magnet, and a galvanometer.

Transformers and the Power Grid

A transformer uses electromagnetic induction to change voltage. A primary coil carries alternating current, creating a continuously changing magnetic field in an iron core. This changing field induces a voltage in a secondary coil wrapped around the same core. The ratio of voltages equals the ratio of the number of turns in each coil.

Step-up transformers increase voltage for long-distance transmission. Step-down transformers reduce voltage for safe household use. Without transformers, it would be impossible to transmit electricity efficiently over long distances — resistance losses are lower at higher voltages (lower current for the same power), making high-voltage transmission necessary for a national grid.

The alternating current (AC) vs. direct current (DC) war of the 1880s, fought between Thomas Edison (DC) and George Westinghouse and Nikola Tesla (AC), was fundamentally about this: AC can be stepped up and down by transformers; DC cannot (without conversion). AC won, and the global power infrastructure is built on it.

Modern Applications

Beyond power generation and motors, electromagnetic induction appears throughout modern technology.

Wireless charging uses induction coils to transfer energy between a charging pad and a phone without physical contact. The pad contains a coil carrying alternating current; the phone contains a receiving coil. The changing magnetic field of the pad induces current in the phone's coil, charging the battery.

Induction cooktops use the same principle to heat pots directly. A coil beneath the cooktop surface generates a changing magnetic field. A compatible (ferromagnetic) pot placed on the surface has eddy currents induced in it by this field. These induced currents flow through the pot's electrical resistance, generating heat in the pot directly — with no heating of the surrounding cooktop surface.

MRI machines use powerful, carefully controlled magnetic fields and radiofrequency pulses to image the inside of the human body. While the imaging principle is different (nuclear magnetic resonance rather than simple induction), the magnet technology, gradient coils, and radiofrequency equipment all rely on Faraday's insights. Read more about MRI technology in our article How MRI Machines Work.

Metal detectors emit a changing magnetic field and detect the eddy currents induced in nearby metal objects — the induced currents create their own magnetic field that the detector measures.

Regenerative braking in electric and hybrid vehicles uses drive motors as generators during deceleration. Applying the brakes causes the motor's rotor to resist rotation, converting kinetic energy back to electrical energy stored in the battery — all through electromagnetic induction.

FAQ

Q: Why did it take Faraday 11 years to discover electromagnetic induction after Oersted's discovery? The key insight — that only changing magnetic fields induce current, not static ones — was non-obvious. Most early experiments used steady currents to create steady magnetic fields, which produced no induction. The conceptual leap to trying time-varying fields took years of failed experiments and a fresh approach. It is also worth noting that Faraday was simultaneously running the Royal Institution, performing numerous other experiments, and giving public lectures throughout this period.

Q: What is the difference between electromagnetic induction and the photoelectric effect? Electromagnetic induction is the generation of current in a conductor by a changing magnetic field — a classical electromagnetic phenomenon. The photoelectric effect is the emission of electrons from a metal when light above a threshold frequency strikes it — a quantum phenomenon that Einstein explained in 1905 using the photon concept. Both involve electricity, but they operate through completely different mechanisms.

Q: Could Faraday's discovery have been made without his experimental approach? Faraday's lack of mathematics may have been an advantage: he was forced to think physically and conceptually rather than manipulating equations. His introduction of field concepts was not derived mathematically — it came from physical intuition about lines of force filling space. Maxwell, who had both mathematical skill and appreciation for Faraday's physical insights, often cited Faraday as the source of the ideas he formalized.

Q: How much of the modern world depends directly on electromagnetic induction? Almost every electrically powered device does, either directly (generators, motors, transformers, wireless charging, induction heating) or indirectly (almost all electricity is generated by electromagnetic induction before reaching any device). The fraction of global GDP that depends on electromagnetic induction is probably north of 50%.

Sources

• Faraday, M. (1831–1832). "Experimental researches in electricity." Philosophical Transactions of the Royal Society. Reproduced in Experimental Researches in Electricity (1839).
• James, F.A.J.L. (2010). Michael Faraday: A Very Short Introduction. Oxford University Press.
• Maxwell, J.C. (1873). A Treatise on Electricity and Magnetism. Oxford University Press.
• Tweney, R.D. (1992). "Inventing the field: Michael Faraday and the creative 'engineering' of electromagnetic field theory." In Inventive Minds: Creativity in Technology.
• Thompson, S.P. (1898). Michael Faraday: His Life and Work. Cassell and Company.