1. Introduction: Where Does the Current in a Cycle Dynamo Come From?
Picture the little dynamo on a bicycle — the small bottle-shaped device that presses against the tyre and lights the lamp. Pedal, and the lamp glows. Stop, and the lamp dies. No battery is hidden anywhere. So where does the current come from?
Inside that dynamo a coil of wire spins between the poles of a magnet. The faster you pedal, the brighter the lamp. Movement goes in, and electric current comes out.
In an earlier topic you saw the opposite story: push current through a wire that sits in a magnetic field, and the wire feels a force (a push). That was the electric motor — current in, motion out. Now we run the whole thing backwards: a wire moving through a magnetic field produces a current. Motion in, current out.
But a current has a direction. Which way does it flow round the wire? You cannot guess it — you need a rule. That rule is Fleming's right-hand rule, and learning to use it is the whole job of this topic.
You can now say what this topic is for: it tells you the direction of the current produced when a wire moves through a magnetic field.