53 résultats pour "electricity"
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Electricity
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INTRODUCTION
Electricity, one of the basic forms of energy.
electrons in the neutral object are attracted to the positive object. Some of these electrons flow to the side of the neutral object that is nearest to the positive object.This side of the neutral object accumulates electrons and becomes negatively charged. Because electrons leave the far side of the neutral object while its protonsremain stationary, that side becomes positively charged. Since the negatively charged side of the neutral object is closest to the positive object, the attraction bet...
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Electricity
chargé e de mettre sous pression le liquide dans les tuyaux. La diff é rence de potentiel, ou tension, ressemble alors à la diff é rence de pression entre deux points d'un circuit d'eau. Elle est not é e « U », et est exprim é e en volts (V). L'intensit é du courant é lectrique peut ê tre assimil é e au d é bit d'eau dans le tuyau. Elle rend compte du nombre de charges qui passent à chaque seconde dans un point du circuit ; elle est souvent not é e « I », et mesur é e...
- Ideas on saving electricity at home
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electricity
Answer: As per the direction of the electric field, it is always from +ve to -ve charge. So, for Q2, the forces are from Q1 to Q2, and Q3 to Q2. F12 = kQ1*Q2/r² = (9 * 10^9 * 8 * -5 * 10^-12)/(0.05)² = -360 * 10^-3/0.0025 = -144 N F32 = kQ3*Q2/r² = (9 * 10^9 * 30* -5 * 10^-12)/(0.1)² = - 1350 * 10^-2/0.01 = - 1350 N So, net force on Q2 is, F = F12 – F32 = -144 - (-1350) = -144 + 1350 = 1206 N 6. Referring to the diagram below. What is the magnitude and direction of the resultant force a...
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Québec - Geography.
facilities. Tributaries south of the St. Lawrence include the Richelieu, the Saint-François, and the Chaudière rivers, which are only a few hundred kilometers long. TheRimouski and Matane rivers, also south of the St. Lawrence, are popular areas for recreation and salmon fishing. In the Canadian Shield, the longest rivers are theRupert, Eastmain, Grande Baleine, and La Grand-Rivière, which is the site of a huge hydroelectric complex. C Coastlines Québec has two systems of saltwater coastline. O...
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Québec - Canadian History.
facilities. Tributaries south of the St. Lawrence include the Richelieu, the Saint-François, and the Chaudière rivers, which are only a few hundred kilometers long. TheRimouski and Matane rivers, also south of the St. Lawrence, are popular areas for recreation and salmon fishing. In the Canadian Shield, the longest rivers are theRupert, Eastmain, Grande Baleine, and La Grand-Rivière, which is the site of a huge hydroelectric complex. C Coastlines Québec has two systems of saltwater coastline. O...
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Vatican City Facts and Figures.
Voting qualificationsLimited to cardinals under 80 years old ConstitutionApostolic Constitution of 1967, effective 1 March 1968 Armed forcesTotal number of military personnel Not available Military expenditures as a share of gross domestic product (GDP) Not available ECONOMYGross domestic product (GDP, in U.S.$) Not available GDP per capita (U.S.$) Not available GDP by economic sectorAgriculture, forestry, fishing Not available Industry Not available Services Not available Employ...
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Maldives Facts and Figures.
Education expenditure as a share of gross national product (GNP) 6.5 percent (1998-1999) Number of years of compulsory schooling 7 years (2002-2003) Number of students per teacher, primary school 20 students per teacher (2002-2003) GOVERNMENTForm of government Republic Voting qualifications Universal at age 21 Constitution 1 January 1998 Armed forcesTotal number of military personnel Not available Military expenditures as a share of gross domestic product (GDP) 6.4 percent (2003) ECON...
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Carbon - chemistry.
Graphite is black and slippery and conducts electricity. In graphite, the atoms form planar, or flat, layers. Each layer is made up of rings containing six carbon atoms.The rings are linked to each other in a structure that resembles the hexagonal mesh of chicken wire. Each atom has three sigma bonds (with 120° between any two ofthe bonds) and belongs to three neighboring rings. The fourth electron of each atom becomes part of an extensive pi bond system. Graphite conducts electricity,because th...
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Hydrogen - chemistry.
Hydrogen gas does not usually react with other chemicals at room temperature. That is, it does not split into two hydrogen atoms to combine with other chemicals. Thebond between the hydrogen atoms is very strong and can only be broken with a large amount of energy. However, when heated with a flame or a spark, hydrogen gaswill react violently with oxygen in the air to produce water in the following reaction: 2H2 + O 2 → 2H 2O This chemical equation shows that two hydrogen molecules (H 2) and o...
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Sudan - country.
B Principal Cities and Political Divisions The principal city is Khartoum, the capital; other major cities include Omdurman and Khartoum North, major industrial centers, and Port Sudan, a seaport on the RedSea. Sudan is divided into 26 states. C Religion and Language About 70 percent of the people of Sudan are Muslims, some 15 percent are Christians, and most of the remainder follow traditional religions. The people of northernSudan are predominantly Sunni Muslims (Sunni Islam). Most of the pe...
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Turbine.
steam turbine has supplanted the reciprocating engine as a prime mover in large electricity-generating plants and is also used as a means of jet propulsion. Steam turbines are used in the generation of nuclear power and in nuclear ship propulsion. They operate with fuel-fired boilers for power generation. In cogenerationapplications requiring both process heat (heat used in an industrial process) and electricity, steam is raised at high pressure in the boiler and extracted from the turbineat the...
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First Aid.
IV SEVERE BLEEDING The presence of blood over a considerable area of a person’s body does not always indicate severe bleeding. The blood may ooze from multiple small wounds or besmeared, giving the appearance of more blood than is actually present. The rate at which blood is lost from a wound depends on the size and kind of blood vesselruptured. Bright red, spurting blood indicates injury to an artery while welling or steadily flowing, dark red blood indicates injury to a vein. Welling or spur...
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Fire - chemistry.
were usually natural caves. Eventually people learned to dip branches in pitch to form torches. They created crude lamps by filling a hollowed out piece of stone withmoss soaked in oil or tallow (a substance derived from animal fat). By cooking with fire, prehistoric people made the meat of the animals they killed more palatable and digestible. They learned to preserve meat by smoking it over a fire,vastly decreasing the danger of periodic starvation. Cooking also enabled them to add some for...
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Television.
A charge-coupled device (CCD) can be much smaller than a camera tube and is much more durable. As a result, cameras with CCDs are more compact and portablethan those using a camera tube. The image they create is less vulnerable to distortion and is therefore clearer. In a CCD, the light from a scene strikes an array ofphotodiodes arranged on a silicon chip. Photodiodes are devices that conduct electricity when they are struck by light; they send this electricity to tiny capacitors. Thecapacitors...
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Yangtze - Geography.
A Agriculture and Industry Today about 400 million people, or about one-third of the population of China, live in the Yangtze Basin. Many are engaged in agriculture. The basin contributes nearlyhalf of China’s crop production, although only one-quarter of the basin is arable. The most fertile areas for farming are the Sichuan Basin, the plains between theYangtze and its tributary the Han, and the plains of the lower basin. In all about 40 percent of the cereals, more than 30 percent of the cott...
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California - geography.
The Basin and Range province is an arid area of mountain ranges, basins, and deserts. In California it is represented primarily by parts of the Great Basin and SonoranDesert sections. Within the Great Basin lies Death Valley, whose lowest elevation, 86 m (282 ft) below sea level, is the lowest point in the Western Hemisphere. TheSonoran Desert section is characterized by numerous flat plains separated by low but rugged ranges. It includes the extensive Mojave, or Mohave, Desert. Also in thisprov...
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California - USA History.
The Basin and Range province is an arid area of mountain ranges, basins, and deserts. In California it is represented primarily by parts of the Great Basin and SonoranDesert sections. Within the Great Basin lies Death Valley, whose lowest elevation, 86 m (282 ft) below sea level, is the lowest point in the Western Hemisphere. TheSonoran Desert section is characterized by numerous flat plains separated by low but rugged ranges. It includes the extensive Mojave, or Mohave, Desert. Also in thisprov...
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Global Warming.
some of the warming influence of increasing greenhouse gases. A1 Carbon Dioxide Carbon dioxide is the second most abundant greenhouse gas, after water vapor. Carbon dioxide constantly circulates in the environment through a variety of naturalprocesses known as the carbon cycle. It is released into the atmosphere from natural processes such as eruptions of volcanoes; the respiration of animals, whichbreathe in oxygen and exhale carbon dioxide; and the burning or decay of plants and other organic...
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Physics
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INTRODUCTION
Physics, major science, dealing with the fundamental constituents of the universe, the forces they exert on one another, and the results produced by these forces.
Starting about 1665, at the age of 23, Newton enunciated the principles of mechanics, formulated the law of universal gravitation, separated white light into colors,proposed a theory for the propagation of light, and invented differential and integral calculus. Newton's contributions covered an enormous range of naturalphenomena: He was thus able to show that not only Kepler's laws of planetary motion but also Galileo's discoveries of falling bodies follow a combination of his ownsecond law of m...
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Magnetism
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INTRODUCTION
Magnetism, an aspect of electromagnetism, one of the fundamental forces of nature.
the French physicist Paul Langevin produced a theory regarding the temperature dependence of the magnetic properties of paramagnets (discussed below), which wasbased on the atomic structure of matter. This theory is an early example of the description of large-scale properties in terms of the properties of electrons and atoms.Langevin's theory was subsequently expanded by the French physicist Pierre Ernst Weiss, who postulated the existence of an internal, “molecular” magnetic field inmaterials...
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Automobile.
Electric motors have been used to power automobiles since the late 1800s. Electric power supplied by batteries runs the motor, which rotates a driveshaft, the shaftthat transmits engine power to the axles. Commercial electric car models for specialized purposes were available in the 1980s. General Motors Corporation introduced amass-production all-electric car in the mid-1990s. Automobiles that combine two or more types of engines are called hybrids. A typical hybrid is an electric motor with ba...
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Alberta - Geography.
C Climate Except for the mountain areas, summers throughout the province are quite warm. Winters are long and extremely cold. In July, average daily temperatures range fromabout 16°C (about 60°F) along the northern boundary to about 21°C (about 70°F) in the south. In the extreme southeastern section of the province, temperatures of43°C (110°F) have been recorded. In January, average daily temperatures range from about -14°C (about 6°F) at Grande Prairie to about -9°C (about 16°F) atCalgary. Tem...
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Alberta - Canadian History.
C Climate Except for the mountain areas, summers throughout the province are quite warm. Winters are long and extremely cold. In July, average daily temperatures range fromabout 16°C (about 60°F) along the northern boundary to about 21°C (about 70°F) in the south. In the extreme southeastern section of the province, temperatures of43°C (110°F) have been recorded. In January, average daily temperatures range from about -14°C (about 6°F) at Grande Prairie to about -9°C (about 16°F) atCalgary. Tem...
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Kiribati Facts and Figures.
Male Not available Education expenditure as a share of gross national product (GNP) 11.4 percent (1996) Number of years of compulsory schooling 10 years (2000) Number of students per teacher, primary school 22 students per teacher (2002-2003) GOVERNMENTForm of government Republic Voting qualifications Universal at age 18 Constitution 12 July 1979 Armed forcesTotal number of military personnel Not available Military expenditures as a share of gross domestic product (GDP) Not available...
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Dominica Facts and Figures.
Male 94 percent (1995) Education expenditure as a share of gross national product (GNP) 5.6 percent (1999-2000) Number of years of compulsory schooling 12 years (2002-2003) Number of students per teacher, primary school 19 students per teacher (2002-2003) GOVERNMENTForm of government Parliamentary democracy Voting qualifications Universal at age 18 Constitution 3 November 1978 Armed forcesTotal number of military personnel Not available Military expenditures as a share of gross domest...
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Molecule - chemistry.
attracted to the negatively charged electrons between them. The electrons belong to the molecule as a whole. However, each hydrogen atom now has a complete outershell of two electrons. The formula H 2 describes a hydrogen molecule, a discrete unit. When a molecule contains just two atoms, such as the hydrogen molecule does, it is called a diatomic molecule. Some atoms can form covalent bonds with more than one other atom and thus create a larger molecule. Atoms form molecules with covalent bo...
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Switzerland - country.
formation over higher elevations. The wind reverses direction about sundown and moves down the valley as a cool downdraft. The foehn, which occurs during the wintermonths, is a dry and relatively warm airflow that is drawn northward over the Alps. The foehn can quickly melt snow and ice, increasing the risk of mudslides andavalanches. D Natural Resources Waterpower is the chief natural resource of Switzerland. The principal source of water is runoff from the considerable annual precipitation th...
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Mississippi - geography.
The climate of Mississippi is characterized by long, hot, and humid summers and generally mild winters. The higher lands in the northeast are usually cooler than otherareas of the state. D1 Temperature Average January temperatures range from about 6° C (about 42° F) in northeastern Mississippi to about 12° C (about 54° F) along the Gulf Coast. No part of the stateis entirely free from freezing temperatures, but prolonged periods of extreme cold rarely occur. Temperatures more than 15° C (30° F)...
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Mississippi - USA History.
The climate of Mississippi is characterized by long, hot, and humid summers and generally mild winters. The higher lands in the northeast are usually cooler than otherareas of the state. D1 Temperature Average January temperatures range from about 6° C (about 42° F) in northeastern Mississippi to about 12° C (about 54° F) along the Gulf Coast. No part of the stateis entirely free from freezing temperatures, but prolonged periods of extreme cold rarely occur. Temperatures more than 15° C (30° F)...
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North Carolina - geography.
The drainage divide in North Carolina follows the Blue Ridge range on the eastern margin of the mountain region. This is called the “Eastern Continental Divide.” West ofthis divide, rivers drain into the Mississippi River through the Tennessee River and other tributaries of the Ohio River. The French Broad, the largest, and the LittleTennessee flow into the Tennessee River. The New River flows into the Kanawha River of West Virginia which in turn flows into the Ohio River. Most of the state’s ri...
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North Carolina - USA History.
The drainage divide in North Carolina follows the Blue Ridge range on the eastern margin of the mountain region. This is called the “Eastern Continental Divide.” West ofthis divide, rivers drain into the Mississippi River through the Tennessee River and other tributaries of the Ohio River. The French Broad, the largest, and the LittleTennessee flow into the Tennessee River. The New River flows into the Kanawha River of West Virginia which in turn flows into the Ohio River. Most of the state’s ri...
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Senegal - country.
Although most of the population works in agriculture, Senegal has a growing industrial sector, one of the largest in West Africa. Nevertheless, two cash crops remain atthe foundation of the economy—peanuts and cotton. Important technical and economic assistance has been provided by France and other countries of the EuropeanUnion and the International Bank for Reconstruction and Development (World Bank). In 2006 the gross domestic product (GDP) was $9.2 billion, or $760.90 a person. A Agriculture...
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Benin - country.
French is the official language of Benin, but most people speak an African language. Each of the country’s ethnic groups has its own language. Fon is the most widelyspoken language. About 52 percent of the population professes traditional religious beliefs, chiefly Vodun, a belief in spirits. Arab merchants introduced Islam to the region, and today it isthe religion of some 20 percent of the people, most of whom live in the north. Christianity, especially Roman Catholicism, is the religion of ab...
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Burkina Faso - country.
powers to promote the welfare of the people. The Lobi live in the southwest as farmers and hunters. Defiant of newcomers, they live in small terraced fortifications. The Bobo are chiefly farmers, artisans, and metalworkers living in large villages in the west-central part of the country. The Gourounsi are mainly artisans and farmers in the south-central areas. Their society is lesshighly structured than that of the other Voltaic groups. Christianity has made substantial inroads among them. The M...
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Burundi - country.
D Way of Life Most Burundians live in self-contained compounds of small round grass huts scattered over the country’s many hills. The rugo , the traditional Tutsi hut, is divided into sections and surrounded by an enclosure and cattle corrals. Families farm scattered plots of land on different soils at different altitudes to minimize crop failure. Thefloors of valleys are avoided due to higher temperatures and tsetse fly infestation. Social roles are largely determined by ethnicity, with the T...
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Artificial Satellite - astronomy.
The first stage of a multistage rocket consists of rocket engines that provide a huge amount of force, or thrust. The first stage lifts the entire launch vehicle—with itsload of fuel, the rocket body, and the satellite—off the launch pad and into the first part of the flight. After its engines use all their fuel, the first stage portion of therocket separates from the rest of the launch vehicle and falls to Earth. The second stage then ignites, providing the energy necessary to lift the satellit...
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Syria - country.
D Education Primary education is free and compulsory for all children aged 6 through 12. Some 78 percent of the adult Syrian population was estimated to be literate in 2005.Primary schools enrolled 2.8 million pupils in the 2000 school year, and 1.1 million students attended secondary schools and vocational institutes. In 1998, 94,110 Syrian students were enrolled in institutes of higher education. Syria has universities in Damascus, Ḩalab, Ḩim ş, and Al L ādhiq īyah. Also in Damascus isthe Ar...
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Submarine.
B Propulsion Modern submarines use either diesel-electric or nuclear power to drive the sub's propeller and to provide internal electric power. Diesel-electric power emerged as themost efficient propulsion system for submarines in the early 20th century, following unsuccessful attempts to use steam or gasoline power. While on the surface, thesubmarine uses a diesel engine to drive the propeller and generate electricity. When submerged, a battery-driven electrical motor takes over for propulsion...
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Bhutan - country.
languages ( see Indo-Iranian Languages) and follow Hinduism. Nepalese people constitute a significant portion of Bhutan’s population. They are the most recent settlers, occupying south central and southwestern Bhutan. TheNepalese are mainly Rai, Gurung, and Limbu ethnic groups from the eastern mountains of Nepal. Nepalese immigration has been banned since 1959, when theBhutanese government feared the minority would become too populous. Nepalese are not permitted to live in the central Middle Hi...
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Poverty.
economic and demographic trends, and (7) welfare incentives. A Overpopulation Overpopulation, the situation of having large numbers of people with too few resources and too little space, is closely associated with poverty. It can result from highpopulation density (the ratio of people to land area, usually expressed as numbers of persons per square kilometer or square mile) or from low amounts of resources, or from both. Excessively high population densities put stress on available resources....
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Light - astronomy.
Each different frequency or wavelength of visible light causes our eye to see a slightly different color. The longest wavelength we can see is deep red at about 700 nm.The shortest wavelength humans can detect is deep blue or violet at about 400 nm. Most light sources do not radiate monochromatic light. What we call white light,such as light from the Sun, is a mixture of all the colors in the visible spectrum, with some represented more strongly than others. Human eyes respond best to greenlight...
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Sweden - country.
mi) and is Sweden’s second largest lake, after Vänern. The two lakes, together with several smaller lakes, rivers, and canals, form an internal water route called theGöta Canal. Built in the early 19th century, the Göta Canal extends for about 386 km (about 240 mi) and provides a scenic transportation link between the Baltic Sea,at Stockholm, and the Kattegat. Sweden’s other large lakes in the district include Mälaren, Hjälmaren, and the famously picturesque Siljan. D Climate Although one-seven...
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World Energy Supply.
In the 1990s, oil production by non-OPEC countries remained strong and production by OPEC countries rebounded. The result at the end of the 20th century was aworld oil surplus and prices (when adjusted for inflation) that were lower than in 1972. Experts are uncertain about future oil supplies and prices. Low prices have spurred greater oil consumption, and experts question how long world petroleum reservescan keep pace with increased demand. Many of the world’s leading petroleum geologists beli...
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Windmill.
James F. ManwellMicrosoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.
- Semiconductor.
- Nikola Tesla.
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Galileo (spacecraft) - astronomy.
Great Red Spot, sustains itself on energy gained from the upper atmosphere, perhaps by absorbing the energy of smaller atmospheric disturbances. In 1999 Galileotook detailed photographs of Io’s volcanic eruptions; scientists hope to use the observations to learn more about similar volcanic activity that occurred on Earth eonsago. Observations taken by Galileo in 2000 lent strength to the theory that Europa may have an ocean of liquid water. The spacecraft’s magnetometer recorded regularchanges i...
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Chemical Reaction - chemistry.
Many groups of elements occur so often as ions that they are given names: nitrate, NO 3-; sulfate, SO 42-; and phosphate, PO 43-. The suffix -ate usually indicates the presence of oxygen. The positive ion, NH 4+, is called ammonium, as in NH 4Cl, ammonium chloride, or (NH 4)3PO4, ammonium phosphate. Rules for naming more complicated compounds exist, but many compounds have been given trivial names—for example, Na 2B4O7·10 H 2O, borax—or proprietary names—F(CF 2)nF, Teflon. These nonsystemat...
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Vermont - geography.
Forests cover 78 percent of Vermont. Most of the trees are deciduous, principally the maple, elm, birch, beech, oak, hickory, ash, cherry, and butternut. The state treeis the sugar maple, which provides Vermont’s famous maple syrup. Conifers are common in some mountain areas and include mainly the white pine, red spruce,hemlock, and cedar. A great variety of ferns have been found within the state. Among the more common wildflowers that grow in Vermont are anemones, arbutuses,violets, lilacs, dai...