electricity je nebrojiva imenica
ETYM Cf. French électricité. Related to Electric.
In electricity, a storage battery —that is, a group of rechargeable secondary cells. A familiar example is the lead–acid automobile battery.
An ordinary 12-volt automobile battery consists of six lead–acid cells which are continually recharged by the car’s alternator or dynamo. It has electrodes of lead and lead oxide in an electrolyte of sulfuric acid. Another common type of accumulator is the “nife” or Ni Fe cell, which has electrodes of nickel and iron in a potassium hydroxide electrolyte.
All phenomena caused by electric charge, whether static or in motion. Electric charge is caused by an excess or deficit of electrons in the charged substance, and an electric current by the movement of electrons around a circuit. Substances may be electrical conductors, such as metals, which allow the passage of electricity through them, or insulators, such as rubber, which are extremely poor conductors. Substances with relatively poor conductivities that can be improved by the addition of heat or light are known as semiconductors.
Electricity generated on a commercial scale was available from the early 1880s and used for electric motors driving all kinds of machinery, and for lighting, first by carbon arc, but later by incandescent filaments (first of carbon and then of tungsten), enclosed in glass bulbs partially filled with inert gas under vacuum. Light is also produced by passing electricity through a gas or metal vapor or a fluorescent lamp. Other practical applications include telephone, radio, television, X-ray machines, and many other applications in electronics.
The fact that amber has the power, after being rubbed, of attracting light objects, such as bits of straw and feathers, is said to have been known to Thales of Miletus and to the Roman naturalist Pliny. William Gilbert, Queen Elizabeth I’s physician, found that many substances possessed this power, and he called it “electric” after the Greek word meaning “amber”.
In the early 1700s, it was recognized that there are two types of electricity and that unlike kinds attract each other and like kinds repel. The charge on glass rubbed with silk came to be known as positive electricity, and the charge on amber rubbed with wool as negative electricity. These two charges were found to cancel each other when brought together.
In 1800 Alessandro Volta found that a series of cells containing brine, in which were dipped plates of zinc and copper, gave an electric current, which later in the same year was shown to evolve hydrogen and oxygen when passed through water (electrolysis). Humphry Davy, in 1807, decomposed soda and potash (both thought to be elements) and isolated the metals sodium and potassium, a discovery that led the way to electroplating. Other properties of electric currents discovered were the heating effect, now used in lighting and central heating, and the deflection of a magnetic needle, described by Hans Oersted 1820 and elaborated by André Ampčre 1825. This work made possible the electric telegraph.
For Michael Faraday, the fact that an electric current passing through a wire caused a magnet to move suggested that moving a wire or coil of wire rapidly between the poles of a magnet would induce an electric current. He demonstrated this 1831, producing the first dynamo, which became the basis of electrical engineering. The characteristics of currents were crystallized about 1827 by Georg Ohm, who showed that the current passing along a wire was equal to the electromotive force (emf) across the wire multiplied by a constant, which was the conductivity of the wire. The unit of resistance (ohm) is named for Ohm, the unit of emf is named for Volta (volt), and the unit of current after Ampčre (amp).
The work of the late 1800s indicated the wide interconnections of electricity (with magnetism, heat, and light), and about 1855 James Clerk Maxwell formulated a single electromagnetic theory. The universal importance of electricity was decisively proved by the discovery that the atom, up until then thought to be the ultimate particle of matter, is composed of a positively charged central core, the nucleus, about which negatively charged electrons rotate in various orbits.
Electricity is the most useful and most convenient form of energy, readily convertible into heat and light and used to power machines. Electricity can be generated in one place and distributed anywhere because it readily flows through wires. It is generated at power stations where a suitable energy source is harnessed to drive turbines that spin electricity generators. Current energy sources are coal, oil, water power (hydroelectricity), natural gas, and nuclear energy. Research is underway to increase the contribution of wind, tidal, and geothermal power. Nuclear fuel has proved a more expensive source of electricity than initially anticipated and worldwide concern over radioactivity may limit its future development.
Electricity is generated at power stations at a voltage of about 25,000 volts, which is not a suitable voltage for long-distance transmission. For minimal power loss, transmission must take place at very high voltage (400,000 volts or more). The generated voltage is therefore increased (“stepped up”) by a transformer. The resulting high-voltage electricity is then fed into the main arteries of the grid system, an interconnected network of power stations and distribution centers covering a large area. After transmission to a local substation, the line voltage is reduced by a step-down transformer and distributed to consumers.
Among specialized power units that convert energy directly to electrical energy without the intervention of any moving mechanisms, the most promising are thermionic converters. These use conventional fuels such as propane gas, as in portable military power packs, or, if refueling is to be avoided, radioactive fuels, as in uncrewed navigational aids and spacecraft.
1. A form of energy associated with moving electrons and protons.
2. Energy made available by the flow of electric charge through a conductor; SYN. electrical energy.
3. Keen and shared excitement.