In each device, a magnet and a coil of wire are employed to change one form of energy into another form. A motor consists of multiple loops of wire placed in a magnetic field. Either the loops or the magnet can rotate. The current through the wires in the field causes a force that results in rotation and thus mechanical energy. Motors in a home are used in fans, hair dryers, and food processors. There are over a hundred motors in a modern automobile. The starter motor is the largest and most powerful.

A generator does the opposite of a motor; it changes mechanical to electrical energy, but still consists of multiple loops of wire in a magnetic field. Either the loops or the magnet can rotate. In an automobile a form of a generator, called an alternator, uses some of energy from the engine to charge the battery. Backup generators use the energy from a gasoline engine to produce enough electrical energy to keep some of the lights and appliances running in a house when the electrical power fails. Electric utilities use huge generators to provide power for a city or larger area. The generators get their energy from steam turbines. The heat required to turn water into steam can come from coal, oil, natural gas, or nuclear “burners.” Wind power uses generators turned by the propeller blades.