1. Introduction: Where Does the Electricity in Your Home Come From?
Switch on a fan, a tube-light, a phone charger — the power flows the moment you flip the switch. No one is pedalling. No battery the size of a building sits under your house. So where is all this electricity made?
In the previous topic you saw one small machine do it: a bicycle dynamo. Spin a coil between the poles of a magnet and a current appears in the coil. Motion in, current out — that is electromagnetic induction (a current produced just by moving a conductor across a magnetic field).
A power station does exactly the same thing, only bigger. Falling water, or steam from burning coal, spins a giant coil between huge magnets. The motion of that coil is the source of almost every unit of electricity you have ever used. That machine is the electric generator.
There are two kinds, and they look almost identical. One gives alternating current (AC) — a current that keeps reversing its direction. The other gives direct current (DC) — a current that always flows the same way. The whole job of this topic is to see what makes the difference, and it comes down to one small part you can point to on a diagram.
You can now say what a generator does: it turns the motion of a coil in a magnetic field into an electric current — and it can be built to give either AC or DC.