Презентация на тему: Electricity

Electricity

References: Jones, D.A., "Electrical engineering: the backbone of society", Proceedings of the IEE: Science, Measurement and Technology 138 (1): 1–10 Moller, Peter (December 1991), "Review: Electric Fish", BioScience 41 (11): 794–6 [794] Bullock, Theodore H. (2005), Electroreception, Springer, pp. 5–7, ISBN 0387231927 Morris, Simon C. (2003), Life's Solution: Inevitable Humans in a Lonely Universe, Cambridge University Press, pp. 182–185, ISBN 0521827043 The Encyclopedia Americana; a library of universal knowledge (1918), New York: Encyclopedia Americana Corp Stewart, Joseph (2001), Intermediate Electromagnetic Theory, World Scientific, p. 50, ISBN 9-8102-4471-1 Simpson, Brian (2003), Electrical Stimulation and the Relief of Pain, Elsevier Health Sciences, pp. 6–7, ISBN 0-4445-1258-6 Frood, Arran (27 February 2003), Riddle of 'Baghdad's batteries', BBC, http://news.bbc.co.uk/1/hi/sci/tech/2804257.stm, retrieved on 2008-02-16 Baigrie, Brian (2006), Electricity and Magnetism: A Historical Perspective, Greenwood Press, pp. 7–8, ISBN 0-3133-3358-0 Chalmers, Gordon (1937), "The Lodestone and the Understanding of Matter in Seventeenth Century England", Philosophy of Science 4 (1): 75–95 Srodes, James (2002), Franklin: The Essential Founding Father, Regnery Publishing, pp. 92–94, ISBN 0895261634 It is uncertain if Franklin personally carried out this experiment, but it is popularly attributed to him.

Uman, Martin (1987) (PDF). All About Lightning. Dover Publications. ISBN 048625237X. http://ira.usf.edu/CAM/exhibitions/1998_12_McCollum/supplemental_didactics/23.Uman1.pdf Kirby, Richard S. (1990), Engineering in History, Courier Dover Publications, pp. 331–333, ISBN 0486264122 Marković, Dragana, The Second Industrial Revolution, http://www.b92.net/eng/special/tesla/life.php?nav_id=36502, retrieved on 2007-12-09 Trefil, James (2003), The Nature of Science: An A-Z Guide to the Laws and Principles Governing Our Universe, Houghton Mifflin Books, p. 74, ISBN 0-6183-1938-7 Duffin, W.J. (1980), Electricity and Magnetism, 3rd edition, McGraw-Hill, pp. 2–5, ISBN 007084111X Sears, et al., Francis (1982), University Physics, Sixth Edition, Addison Wesley, p. 457, ISBN 0-2010-7199-1 "The repulsive force between two small spheres charged with the same type of electricity is inversely proportional to the square of the distance between the centres of the two spheres." Charles-Augustin de Coulomb, Histoire de l'Academie Royal des Sciences, Paris 1785. Duffin, W.J. (1980), Electricity and Magnetism, 3rd edition, McGraw-Hill, p. 35, ISBN 007084111X National Research Council (1998), Physics Through the 1990s, National Academies Press, pp. 215–216, ISBN 0309035767 Umashankar, Korada (1989), Introduction to Engineering Electromagnetic Fields, World Scientific, pp. 77–79, ISBN 9971509210 Hawking, Stephen (1988), A Brief History of Time, Bantam Press, p. 77, ISBN 0-553-17521-1

23. Shectman, Jonathan (2003), Groundbreaking Scientific Experiments, Inventions, and Discoveries of the 18th Century, Greenwood Press, pp. 87–91, ISBN 0-3133-2015-2 24. Sewell, Tyson (1902), The Elements of Electrical Engineering, Lockwood, p. 18. The Q originally stood for 'quantity of electricity', the term 'electricity' now more commonly expressed as 'charge'.Close, Frank (2007), The New Cosmic Onion: Quarks and the Nature of the Universe, CRC Press, p. 51, ISBN 1-5848-8798-2Ward, Robert (1960), Introduction to Electrical Engineering, Prentice-Hall, p. 18 Solymar, L. (1984), Lectures on electromagnetic theory, Oxford University Press, p. 140, ISBN 0-19-856169-5 Duffin, W.J. (1980), Electricity and Magnetism, 3rd edition, McGraw-Hill, pp. 23–24, ISBN 007084111X Berkson, William (1974), Fields of Force: The Development of a World View from Faraday to Einstein, Routledge, p. 370, ISBN 0-7100-7626-6 Accounts differ as to whether this was before, during, or after a lecture. Bird, John (2007), Electrical and Electronic Principles and Technology, 3rd edition, Newnes, p. 11, ISBN 0-978-8556-6 Bird, John (2007), Electrical and Electronic Principles and Technology, 3rd edition, Newnes, pp. 206–207, ISBN 0-978-8556-6 Bird, John (2007), Electrical and Electronic Principles and Technology, 3rd edition, Newnes, pp. 223–225, ISBN 0-978-8556-6 Sears, et al., Francis (1982), University Physics, Sixth Edition, Addison Wesley, pp. 469–470, ISBN 0-2010-7199-1 Sears, et al., Francis (1982), University Physics, Sixth Edition, Addison Wesley, p. 479, ISBN 0-2010-7199-1

Electricity

Electricity (from New Latin ēlectricus, "amber-like") is a general term that encompasses a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena such as lightning and static electricity, but in addition, less familiar concepts such as the electromagnetic field and electromagnetic induction.

In general usage, the word 'electricity' is adequate to refer to a number of physical effects. However, in scientific usage, the term is vague, and these related, but distinct, concepts are better identified by more precise terms:

Electric charge – a property of some subatomic particles, which determines their electromagnetic interactions. Electrically charged matter is influenced by, and produces, electromagnetic fields Electric current – a movement or flow of electrically charged particles, typically measured in amperes. Electric field – an influence produced by an electric charge on other charges in its vicinity. Electric potential – the capacity of an electric field to do work, typically measured in volts. Electromagnetism – a fundamental interaction between the electric field and motion of electric charge.

Electricity has been studied since antiquity, though scientific advances were not forthcoming until the seventeenth and eighteenth centuries. It would remain however until the late nineteenth century that engineers were able to put electricity to industrial and residential use, a time which witnessed a rapid expansion in the development of electrical technology. Electricity's extraordinary versatility as a source of energy means it can be put to an almost limitless set of applications which include transport, heating, lighting, communications. The backbone of modern industrial society is, and for the foreseeable future can be expected to remain, the use of electrical power .

Benjamin Franklin conducted extensive research on electricity in the 18th century

Electric circuits

An electric circuit is an interconnection of electric components, usually to perform some useful task, with a return path to enable the charge to return to its source. The components in an electric circuit can take many forms, which can include elements such as resistors, capacitors, switches, transformers and electronics. Electronic circuits contain active components, usually semiconductors, and typically exhibit non-linear behaviour, requiring complex analysis. The simplest electric components are those that are termed passive and linear: while they may temporarily store energy, they contain no sources of it, and exhibit linear responses to stimuli. A basic electric circuit. The voltage source V on the left drives a current I around the circuit, delivering electrical energy into the resistance R. From the resistor, the current returns to the source, completing the circuit.

The inductor is a conductor, usually a coil of wire, that stores energy in a magnetic field in response to the current flowing through it. The capacitor is a device capable of storing charge, and thereby storing electrical energy in the resulting field. It consists of two conducting plates separated by a thin insulating layer; in practice, thin metal foils are coiled together, increasing the surface area per unit volume and therefore the capacitance. The unit of capacitance is the farad, named after Michael Faraday, and given the symbol F: one farad is the capacitance that develops a potential difference of one volt when it stores a charge of one coulomb. When the current changes, the magnetic field does too, inducing a voltage between the ends of the conductor. The induced voltage is proportional to the time rate of change of the current. The constant of proportionality is termed the inductance. The unit of inductance is the henry, named after Joseph Henry, a contemporary of Faraday. One henry is the inductance that will induce a potential difference of one volt if the current through it changes at a rate of one ampere per second

Production and usesGenerationElectrical energy is usually generated by electro-mechanical generators driven by steam produced from fossil fuel combustion, or the heat released from nuclear reactions; or from other sources such as kinetic energy extracted from wind or flowing water. Such generators bear no resemblance to Faraday's homopolar disc generator of 1831, but they still rely on his electromagnetic principle that a conductor linking a changing magnetic field induces a potential difference across its ends. The invention in the late nineteenth century of the transformer meant that electricity could be generated at centralized power stations, benefiting from economies of scale, and be transmitted across countries with increasing efficiency. Since electrical energy cannot easily be stored in quantities large enough to meet demands on a national scale, at all times exactly as much must be produced as is required. This requires electricity utilities to make careful predictions of their electrical loads, and maintain constant coordination with their power stations.

Demand for electricity grows with great rapidity as a nation modernizes and its economy develops. The United States showed a 12% increase in demand during each year of the first three decades of the twentieth century, a rate of growth that is now being experienced by emerging emerging economies such as those of India or China. Historically, the growth rate for electricity demand has outstripped that for other forms of energy, such as coal.

Uses

Electricity is an extremely flexible form of energy, and it may be adapted to a huge, and growing, number of uses. The invention of a practical incandescent light bulb in the 1870s led to lighting becoming one of the first publicly available applications of electrical power. Although electrification brought with it its own dangers, replacing the naked flames of gas lighting greatly reduced fire hazards within homes and factories. Public utilities were set up in many cities targeting the burgeoning market for electrical lighting.

Electricity is used within telecommunications, and indeed the electrical telegraph, demonstrated commercially in 1837 by Cooke and Wheatstone, was one of its earliest applications. With the construction of first intercontinental, and then transatlantic, telegraph systems in the 1860s, electricity had enabled communications in minutes across the globe.

Optical fibre and satellite communication technology have taken a share of the market for communications systems, but electricity can be expected to remain an essential part of the process.

Electricity and the natural world Physiological effects

A voltage applied to a human body causes an electric current to flow through the tissues, and although the relationship is non-linear, the greater the voltage, the greater the current. The threshold for perception varies with the supply frequency and with the path of the current, but is about 1 mA for mains-frequency electricity.If the current is sufficiently high, it will cause muscles contraction, fibrillation of the heart, and tissue burns. The lack of any visible sign that a conductor is electrified makes electricity a particular hazard.

The pain caused by an electric shock can be intense, leading electricity at times to be employed as a method of torture. Death caused by an electric shock is referred to as electrocution. Electrocution is still the means of judicial execution in some jurisdictions, though its use has become in recent times.

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