How did Michael Faraday show that a changing magnetic field can induce electric current?

In 1831, Michael Faraday demonstrated that a changing magnetic field induces an electric current through a series of experiments involving an electromagnet and a galvanometer.12

His most famous experiment involved winding an iron ring with two separate coils of insulated wire. He connected one coil to a battery and the other to a galvanometer. Faraday observed that when he closed the primary circuit, the galvanometer needle deflected, indicating that a current had been induced in the secondary coil. He was further surprised to see the needle jump in the opposite direction when he opened the circuit, demonstrating that the induction occurred during the growth and collapse of the magnetic field.12

Faraday also proved that this effect could be achieved using a permanent magnet. By moving a magnet into and out of a coil of wire, he induced a current in the wire while the magnet was in motion. He concluded that the electrical effects were caused by changing magnetic flux—the number of "lines of force" cutting across the circuit—which became the basis for Faraday’s law of induction.12