An electrical generator is a device that generates electricity from mechanical energy, usually via electromagnetic induction. Electromagnetic induction works by forcibly moving a loop of wire (a rotor) around a stationary bar (a stator) that provides an electric field, either through a permanent magnet or an electromagnet. By Faraday's law, this induces a current in the rotor, which can be used to power machinery or charge batteries. Possible sources of mechanical energy include steam engines, water falling through a turbine or waterwheel, an internal combustion engine, a hand crank, a wind turbine, compressed air, solar energy, and many others. The electrical generator is the foundation of our modern electrical society. If electrical generators were to cease operating, so would most of the economy.
The electrical generator was first invented by the Hungarian inventor and engineer Anyos Jedlik sometime between 1827 and 1830. Jedlik invented the generator, a simple dynamo, at least six years before Warner von Siemens in Germany and Charles Wheatstone in Britain, whose names are usually associated with the device's invention. Though the electrical generator was invented around 1830, it wouldn't be until Nikola Tesla's pioneering work on rotating magnetic fields around 1882 that generators would become suitable for industrial use. The electrification of the United States occurred in the 1890s, helping cause the Second Industrial Revolution, with which electricity is strongly associated.
Today, there exist electrical generators of all imaginable sizes, from 3-6 watt generators to power bicycle lights to the hydroelectric generators in the Three Gorges Dam in China, which will provide 22.5 gigawatts of power when they are fully installed in 2012. The current worldwide production of electricity is about 20,000 terawatt-hours, with about 66% generated through thermal (burning of fossil fuels), 16% through hydro, 15% through nuclear, and 2% through renewables such as wind or solar power. For environmental and health reasons, worldwide efforts are underway to expand electrical production from hydro, nuclear, and renewable sources and contract electrical production from fossil fuel sources.