Families, businesses, and factories need lots of electricity. Megawatts! Batteries could never supply this need. A whole wall full of batteries would be needed just to power the lighting in a house or classroom–and they would have to be changed every hour! To produce the kind of electricity we take for granted when we flip the switch, we depend on huge generators.

Generators have two coils of wire, each with thousands of windings. The stator is a tube-shaped coil that does not move. Another coil called the rotor is inside the stator. The rotor spins at 3600 rpm (revolutions per minute) and pulls electrons though the stator coils. The flow of electrons through the stator coils produces 14,000 volts of alternating current (AC). The AC electrical system in the United States changes back and forth from positive to negative voltage sixty times each second.