A generator can be broadly defined as a device that converts a form of energy into electricity. Nearly all of the electricity consumers use is produced by generators that convert kinetic (mechanical) energy into electrical energy. Generators operate because of the relationship between magnetism and electricity. In 1831，scientist Michael Faraday discovered that when a magnet is moved inside a coil of wire, an electric current flows in the wire.
The most widely used method of producing electricity uses generators with an electromagnet-a magnet produced by electricity-not a traditional magnet. The generator has a series of insulated coils of wire that form a stationary cylinder. This cylinder surrounds a rotary electromagnetic shaft. When the electromagnetic shaft rotates, it induces a small electric current in each section of the wire coil. Each section of the wire coil becomes a small, separate electric conductor. The small currents of the individual sections are added together to form one large current. This current is the electricity that is transmitted from generators to consumers.
An electric power plant uses a turbine or other similar machine to drive these types of generators. There are steam turbines, gas combustion turbines, water turbines, and wind turbines. Steam turbines using biomass, coal, geothermal energy, natural gas, nuclear energy, and solar thermal energy produce about 70% of the electricity used in the United States. These power plants are about 35% efficient. That means that for every 100 units of primary heat energy that go into a power plant, only 35 units are converted to useable electrical energy.
Other types of devices that generate or produce electricity include electrochemical batteries, fuel cells, solar photovoltaic cells, and thermoelectric generators.
Magnets and Electricity
The spinning of the electrons around the nucleus of an atom creates a tiny magnetic field. The electrons in most objects spin in random directions, and their magnetic forces cancel out each other. Magnets are different because the molecules in magnets are arranged so that their electrons spin in the same direction. This arrangement and movement creates a magnetic force that flows from a north-seeking pole and a south-seeking pole. The magnetic force creates a magnetic field around a magnet.
原子中，电子围绕原子核旋转会产生一个微弱的磁场。大多数物体中电子无 规律旋转，因而它们产生的磁力相互抵消。而磁体有所不同。磁体内部的分子排 布使其电子朝一个方向旋转。这种排布和运动产生了由北极指向南极的磁力。这 种磁力在磁体周围形成磁场。
Have you ever held two magnets close to each other? They don’t act like most objects. If you try to push the same poles together, they repel each other. But if you put different poles together, the magnets will stick together because the north and south poles are attracted to each other. Just like protons and electrons-opposites attract with magnets.
Magnetic fields can be used to make electricity磁场可以用来发电
The properties of magnets can be used to make electricity. Moving magnetic fields can pull and push electrons. Metals such as copper have electrons that are loosely held, so the electrons in copper wires can easily be pushed from their shells by moving magnets.
By using moving magnets and copper wire together, electric generators create electricity. Electric generators essentially convert kinetic energy (the energy of motion) into electrical energy.