To generate something is to create it from other ingredients. You might generate a short story using snippets of ideas about the world around you; people generate plans for their lives based on information they assemble from a variety of sources.
A generator, in everyday language, is an entity that is capable of producing power, usually electricity, for human endeavors. Since power and energy cannot, unfortunately, be created from nothing, generators themselves must be powered by an external source of some kind, energy that is then channeled into usable electricity. If you have ever spent time camping in a cabin owned by well-prepared people, you may be familiar with the concept of a gas-powered generator. Today, a variety of types of generators exist, but all of them rely on the same fundamental physical generator working principles.
In 1831, the physicist Michael Faraday discovered that when a magnet is moved inside a coil of wire, electrons "flow" inside the wire, with this movement called electric current. A generator is any machine that converts energy to electric current, but regardless of the source of this energy – be it coal, hydro or wind power – the ultimate reason electrical current is generated is through motion within a magnetic field.
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In all likelihood, you have seen magnets in action in some way – perhaps the small, rectangular magnets used in home and office settings to affix items of interest to refrigerators. A special kind of cylinder-shaped magnet, called an electromagnet, is placed around a series of insulated coils of conducting wire (such as a copper wire) that are wrapped around a central shaft. Each of these many coils, then, is like a ring surrounding the shaft and oriented at a right angle to the axis of the shaft, much like the relationship of tires to the axle that holds them. When the shaft connected to the wires rotates, a current is generated, because the cylindrical electromagnet outside the wires does not rotate along with them, thus establishing relative movement between a magnetic field and charges inside the conducting wire.
The same thing would happen if the source of a magnetic field moved in the vicinity of a stationary wire or wires. It does not matter which is moving, the magnet or the wire (or both), so long as there is relative, ongoing movement between them.
The Electric Generator: Why?
Why is the ongoing generation of electricity always a concern? Why is it that you know that your life will be interrupted and probably disrupted if "the power goes out" for more than a day or so? The simple answer is that, while humans can store tremendous amounts of fossil fuels such as natural gas and oil for use in emergencies, there is no good way to store large amounts of electricity. You quite likely have a version of humankind's best attempt to store electricity within reach, which is a battery. But while batteries, like everything else in the world of technology, have grown more potent and longer-lasting over time, they are extremely limited in terms of their capacity to sustain the kind of massive voltage outputs required to power whole cities and modern economies.
As a result of there being no reliable way to store electricity, in the modern world, there must always be ways of producing it from raw materials. This is why most businesses, depending on their nature, have backup generators in case the ambient town supply is interrupted. While a baseball-card shop losing power for an hour might not be catastrophic, consider the effects in a hospital intensive-care unit in which electricity-powered machines are literally keeping people alive through breathing for them and other vital functions.
The Physics of Electricity
Picture two large, cube-shaped magnets placed a meter apart, one with its south pole facing the north pole of the other and thereby creating a strong, additive magnetic field between them. This field points toward the north pole and, and if the ends of the magnets are perfectly vertical in relation to the floor, the magnetic field direction is parallel to the floor, like a stack of invisible carpets. If a conducting wire standing straight up is moved through the space between the magnets and remains exactly 0.5 meters from each, the motion of the wire is perpendicular to the magnetic field and current is generated along the wire. The magnetic field, wire movement and current direction (and that of the wire) are thus mutually perpendicular.
The important takeaway from this is that this magnet-wire arrangement is perfectly set up to generate a steady supply of electricity as long as the central shaft continues to rotate, moving the wires coiled inside the cylindrical magnet in such a way as to ensure a steady flow of current through the wires and to an external machine, home or whole power grid. The trick here, of course, is providing the power for the shaft to spin. Engineers have produced a variety of different kinds of generators that make use of different power sources.
Types of Generators
Electric generators can be divided into thermal generators, which make use of heat to generate electricity, and kinetic generators, which make use of the energy of motion to produce electricity. (Note that heat, work and energy all have the same units – usually joules or a multiple thereof, but sometimes calories, ergs or British thermal units [BTU]. Power is energy per unit time and is typically in watts or horsepower.)
Thermal generators: Fossil-fuel generators are the industry standard and are powered by the burning of coal, petroleum (oil) or natural gas. These fuels are plentiful but finite, and they create a host of environmental and health problems that have spurred humanity to come up with alternatives. Cogeneration involves piping the waste steam from these kinds of plants to customers who use the steam for their own smaller generators. Nuclear power is the harnessing of the energy released during nuclear fission, a "clean" but controversial process. Natural gas generators produce electricity without producing steam and can be combined with steam generation. Biomass plants, in which non-traditional items are used as fuel (such as wood or plant matter), have gained momentum in the beginning of the 21st century.
Kinetic generators: The two main kinds of kinetic electricity generators are hydroelectric plants and wind power (or wind turbines). Hydroelectric plants rely on the the flow of water to spin the shafts inside generators. Because few rivers flow throughout the year at anything resembling a steady rate, most of these facilities involve artificial lakes created by dams (such as Lake Mead in southern Nevada and northern Arizona, formed by Hoover Dam) so that the flow across the turbines can be artificially manipulated in accordance with area needs. Wind power has the advantage of not disrupting local land and wildlife in the same way artificial lakes do, but air is much less efficient than water at generating power, and it also carries the problem of varying levels and speeds of wind. While "windmill farms" can involve a number of turbines linked together to create a certain level of power, wind power sufficient to provide electricity to sizable communities was not yet feasible as of 2018.