Move a magnet through a coil of wire and a current flows. The current stops when the magnet stops. Move it faster and the current grows. That is electromagnetic induction, the production of an electric current by a changing magnetic field. Michael Faraday discovered it in 1831, and it became the basis of the electric generator, the transformer, and the induction motor. Without it, the modern power grid would not exist.

Faraday's law says that the induced voltage in a circuit is proportional to the rate of change of magnetic flux through the circuit. Change the flux faster and you get more voltage. Change the number of turns in the coil and you scale the voltage up or down. Lenz's law gives the direction of the induced current. It opposes the change that produced it. That opposition is why generators require mechanical work to turn. The work overcomes the magnetic resistance, and the energy becomes electrical. Induction is also how wireless charging works. A changing current in a coil creates a changing magnetic field, which induces a current in a nearby coil.

Induction facts

• Discovery. Michael Faraday, 1831.
• Faraday's law. Induced voltage proportional to rate of change of flux.
• Lenz's law. Induced current opposes the change that produced it.
• Applications. Generators, transformers, induction motors, wireless charging.

Electromagnetic induction is not the same as static electricity. Static electricity involves stationary charge. Induction involves changing magnetic fields and moving charge.