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Electricity is a fundamental form of energy occurring naturally (as in lightning) or produced artificially, and results from the motion of electrically charged particles of matter. These charges are either neutral, positive, or negative. Electricity is concerned with the positively charged particles, such as protons, that repel one another and the negatively charged particles, such as electrons, that also repel one another. Negative and positive particles, however, attract each other. This behavior may be summarized as follows: Like charges repel, and unlike charges attract.
An electron is a negatively charged elementary particle; it is a constituent of all atoms. The electrons in each atom surround the nucleus in groupings called shells; in a neutral atom the number of electrons is equal to the number of protons in the nucleus. This electron structure is responsible for the chemical properties of the atom; chemical interactions take place between the outer electrons of atoms. Electrons have an electrical charge and when they move, they generate an electric current. Because the electrons of an atom determine the way in which it interacts with other atoms, they play a fundamental part in chemistry.
They were discovered by J J Thomson in 1897 through studying cathode rays (now called electron beams) in electric and magnetic fields. A heated wire filament can be made to emit electrons, and if this is done in a vacuum their paths can be controlled by electric or magnetic fields. Such beams of electrons are used to operate television picture tubes and electron microscopes.
Electric charge which builds up on an insulator and is thus unable to flow is termed static electricity. Like-charged objects repel and opposite-charged objects attract one another. Static electricity is a class of phenomena involving the imbalanced charge present on an object, typically referring to charge with voltages of sufficient magnitude to produce visible attraction, repulsion, and sparks. Static electricity can be seen at work when hair is combed on a cold, dry day. As the comb is pulled through thehair, strands of hair stand out stiffly. Some kind of force seems to pull the hair upward toward the comb.
Rubbing action creates charged objects because it tears electrons loose from some kinds of atoms and transfers them to others. In the case of plastic rubbed with wool, electrons are taken from the wool and pile up on the plastic, giving the plastic a net negative charge and leaving the wool charged positively. When glass is rubbed with silk, the glass loses electrons and the silk gains, producing glass that is charged positively and silk that is charged negatively.
Electric current consists of charge particles - usually electrons - moving through a conductor. Between collections of positive and negative charges there exists a potential difference called 'voltage'. If a conducting path exists between two charged groups, charges will flow from one to the other, constituting an electric current, and usually consists of a flow of electrons from the more negatively charged body to the more positively charged one. Metals and other materials that allow the flow of electric charge through them are known as conductors. Materials that resist the passage of an electric current are known as insulators.
A direct current (DC) is a constant flow between two points having a different electrical potential and the charge flow is one way, as from a battery. Or it may be alternating current (AC), as from a mains supply. Here, the charge flows alternately backwards then forwards in a circuit many times every second. By convention, a positive current is defined as that which flows from a higher potential to a lesser one, driven by the potential difference.
Branch of science that deals with the emission of electrons from conductors and semiconductors, with the subsequent manipulation of these electrons, and with the construction of electronic devices.
Electronics developed out of 19th-c experiments with electricity, which resulted in the invention of thermionic valve, or vacuum tube, in which electrons moved in a vacuum, and led to such inventions as radio, television, radar, and the digital computer.
The diode and other thermionic valves were responsible for the development of radio and other communications media. The iconoscope, an early device for the production of electronic images, led to the development of television, and by the 1930s television broadcasting had begun. Replacement of valves with the comparatively tiny and reliable transistor from 1948 revolutionized electronic development. They were superseded by transistors, introduced at Bell Laboratories in 1948. Transistors facilitated the miniaturization of electronic components, as did the silicon chip and the integrated circuit.
The integrated circuit was developed in 1959. Modern electronic devices are based on minute integrated circuits (silicon chips), wafer-thin crystal slices holding tens of thousands of electronic components. By using solid-state devices such as integrated circuits, extremely complex electronic circuits can be constructed, leading to the development of digital watches, pocket calculators, powerful microcomputers, and word processors
After World War II, communications technology continued to develop, but electronics also found applications in a wide range of other industries. The social impact of electronics is far-reaching, including the development of television, computerized office systems, video games, personal computers, pacemakers, and spacecraft.