Electric generators

Moving a magnet into or out of a coil makes a current flow in it, with no battery: only a changing magnetic field inside the coil does it, so a magnet resting inside makes none, and pulling it out sends the current the other way. This is electromagnetic induction, found by Michael Faraday. A faster movement, a stronger magnet or more turns make a bigger current. A generator keeps it going by spinning coils between magnets, or a magnet inside coils: it turns kinetic energy into electrical energy, the reverse of a motor. A bicycle dynamo is a small one; in power stations huge generators are turned by turbines driven by steam, falling water or wind.