Реферат: Electricity Essay Research Paper WHAT IS ELECTRICITYElectricity

Electricity Essay, Research Paper

WHAT IS ELECTRICITY

Electricity is a form of energy. That’s because we can use electricity to do things for us, like run machines and computers. Electricity also can be transformed into other types of energy such as heat or light and is used to heat our homes, light our cities and towns and power the computers we are using.

Electricity is the type of energy that is invisible. It’s made of moving electrons that are so small and move so fast that we cannot see them.

The electricity that GPU provides travels through the wires you see on tall poles and towers around your town or city. Sometimes they go down in a fenced-off area that is full of large metal boxes, lots of electrical wires, equipment and other stuff. These areas are called substations, and they change the power of electricity is before it gets to your home.

Electricity is the movement of billions of electrons. Electrons are one component of an atom. Atoms are the basic building blocks of all matter and are comprised on protons and neutrons in addition to electrons. The protons and neutrons of an atom are housed in the centre of an atom called the nucleus.

Electricity is a phenomenon that is a result of the existence of electrical charge. The theory of electricity and its inseparable effect, magnetism, is probably the most accurate and complete of all scientific theories. The understanding of electricity has led to the invention of motors, generators, telephones, radio and television, X-ray devices, computers, and nuclear energy systems. Electricity is a necessity to modern civilization.

How is Electricity Produced?

Electricity is a secondary source of energy that is created at a generating plant. At the generating station, primary sources of energy, which include coal, oil, gas, water, and wind, are converted to steam. This steam provides the power to turn the blades of a device known as a turbine. The steam turning the blades of a turbine is like the wind turning the blades of a windmill. The mechanical power created by the steam turning the turbine turns the shaft. The shaft then turns the generator. A generator contains a magnet surrounded by a coil of wire. The movement of electrons is called electric current.

Electric Charge

Amber is a yellowish, translucent mineral. As early as 600 BC the Greeks were aware of its peculiar property: when rubbed with a piece of fur, amber develops the ability to attract small pieces of material such as feathers. For centuries this strange, inexplicable property was thought to be unique to amber.

Two thousand years later, in the 16th century, William Gilbert proved that many other substances are electric (from the Greek word for amber, elektron) and that they have two electrical effects. When rubbed with fur, amber acquires resinous electricity; glass, however, when rubbed with silk, acquires vitreous electricity. Electricity repels the same kind and attracts the opposite kind of electricity. Scientists thought that the friction actually created the electricity (their word for charge). They did not realize that an equal amount of opposite electricity remained on the fur or silk.

In 1747, Benjamin Franklin in America and William Watson (1715-87) in England independently reached the same conclusion: all materials possess a single kind of electrical “fluid” that can penetrate matter freely but that can be neither created nor destroyed. The action of rubbing merely transfers the fluid from one body to another, electrifying both. Franklin and Watson originated the principle of conservation of charge: the total quantity of electricity in an insulated system is constant.

Franklin defined the fluid, which corresponded to vitreous electricity, as positive and the lack of fluid as negative. Therefore, according to Franklin, the direction of flow was from positive to negative–the opposite of what is now known to be true. A subsequent two-fluid theory was developed, according to which samples of the same type attract, whereas those of opposite types repel.

Benjamin Franklin (1706-90) was an American printer, author, philosopher, diplomat, scientist, and inventor. (The Bettmann Archive)

Lightning

Franklin was acquainted with the Leyden jar, a glass jar coated inside and outside with tinfoil. It was the first capacitor, a device used to store charge. The Leyden jar could be discharged by touching the inner and outer foil layers simultaneously, causing an electrical shock to a person. If a metal conductor was used, a spark could be seen and heard. Franklin wondered whether lightning and thunder were also a result of electrical discharge. During a thunderstorm in 1752, Franklin flew a kite that had a metal tip. At the end of the wet, conducting hemp line on which the kite flew he attached a metal key, to which he tied a non-conducting silk string that he held in his hand. The experiment was extremely hazardous, but the results were unmistakable: when he held his knuckles near the key, he could draw sparks from it. The next two who tried this extremely dangerous experiment were killed.

The Electrical Force

It was known as early as 1600 that the attractive or repulsive force diminishes as the charges are separated. This relationship was first placed on a numerically accurate, or quantitative, foundation by Joseph Priestley, a friend of Benjamin Franklin. In 1767, Priestley indirectly deduced that when the distance between two small, charged bodies is increased by some factor, the forces between the bodies are reduced by the square of the factor. For example, if the distance between charges is tripled, the force decreases to one-ninth its former value. Although rigorous, Priestley’s proof was so simple that he did not strongly advocate it. The matter was not considered settled until 18 years later, when John Robinson of Scotland made more direct measurements of the electrical force involved.

Coulomb’s Law

The French physicist Charles A. de Coulomb, whose name is used as the unit of electrical charge, later performed a series of experiments that added important details, as well as precision, to Priestley’s proof. He also promoted the two-fluid theory of electrical charges, rejecting both the idea of the creation of electricity by friction and Franklin’s single-fluid model.

Today the electrostatic force law, also known as COULOMB’S LAW, is expressed as follows: if two small objects, a distance r apart, have charges p and q and are at rest, the magnitude of the force F on either is given by F = Kpq/rr, where K is a constant. According to the International System of Units, the force is measured in newtons (1 Newton = 0.225 lb), the distance in meters, and the charges in coulombs. The constant K then becomes 8.988 billion. Charges of opposite sign attract, whereas those of the same sign repel.

A coulomb C is a large amount of charge. To hold a positive coulomb (+ C) 1 meter away from a negative coulomb (- C) would require a force of 9 billion newtons (2 billion pounds). A typical charged cloud about to give rise to a lightning bolt has a charge of about 30 coulombs.

Electric Potential

Because of an accident the 18th-century Italian scientist Luigi Galvani started a chain of events that culminated in the development of the concept of voltage and the invention of the battery. In 1780 one of Galvani’s assistants noticed that a dissected frog leg twitched when he touched its nerve with a scalpel. Another assistant thought that he had seen a spark from a nearby charged electric generator at the same time. Galvani reasoned that the electricity was the cause of the muscle contractions. He mistakenly thought, however, that the effect was due to the transfer of a special fluid, or “animal electricity,” rather than to conventional electricity.

Experiments such as this, in which the legs of a frog or bird were stimulated by contact with different types of metals, led Luigi Galvani in 1791 to propose his theory that animal tissues generate electricity. (The Bettmann Archive)

The Battery

In experimenting with what he called atmospheric electricity, Galvani found that a frog muscle would twitch when hung by a brass hook on an iron lattice. Another Italian, Alessandro Volta, a professor at the University of Pavia, affirmed that the brass and iron, separated by the moist tissue of the frog, were generating electricity, and that the frog’s leg was simply a detector. In 1800, Volta succeeded in amplifying the effect by stacking plates made of copper, zinc, and moistened pasteboard respectively and in so doing he invented the battery.

A battery separates electrical charge by chemical means. If the charge is removed in some way, the battery separates more charge, thus transforming chemical energy into electrical energy. A battery can affect charges, for instance, by forcing them through the filament of a light bulb. Its ability to do work by electrical means is measured by the volt, named for Volta. A volt is equal to 1 joule of work or energy (1 joule = 2.78/10,000,000 kilowatt-hours) for each coulomb of charge. The electrical ability of a battery to do work is called the electromotive force, or emf.

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