Video narration
How can turning a bicycle wheel make its lamp light? Inside a generator, the wheel turns a coil between a magnet's poles. The coil isn't making magnetism; as it spins, its position in the magnetic field keeps changing. That change pushes electrical charges around the wire, creating a voltage-and in a closed circuit, a current. Here's the key: after half a turn, the coil moves through the field the opposite way, so the current reverses direction. To get that changing current out while the coil keeps spinning, each end connects to slip rings, rings that turn with the coil. Brushes, fixed contacts that touch the rings, carry the current into the external circuit. So the wheel's motion can power a lamp because a rotating coil in a magnetic field makes electricity. Its current reverses every half-turn: that's AC, alternating current.