1. Introduction: The Magnet That Makes Current From Nothing
Picture a small coil of copper wire — just a loop wound a few times round — lying on the table. Its two ends are joined to a galvanometer. A galvanometer is a meter whose needle swings to show even a tiny current; needle in the middle means no current. There is no cell anywhere. Nothing is connected to any battery.
Now you take a bar magnet and push it toward the coil. The instant the magnet moves in, the galvanometer needle kicks to one side. Current is flowing in that coil — and you never gave it a battery.
Stop scrolling. Try it in your head before reading on. Where did that current come from? No cell, no plug, no push from a hand on the wire — only a magnet moving nearby.
That is the whole topic. A moving magnet can make a current appear in a wire it never touches. This is called electromagnetic induction: electro (it makes electric current), magnetic (a magnet causes it), induction (the current is brought into being from a distance, not switched on directly). By the end you will be able to say exactly when this current appears, which way it flows, and how to make it bigger.