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The electronic–hydraulic analogy (derisively referred to as the drain-pipe theory by Oliver Lodge) 〔 Paul J. Nahin, ''Oliver Heaviside: The Life, Work, and Times of an Electrical Genius of the Victorian Age'', JHU Press, 2002 ISBN 0801869099 page 59 〕 is the most widely used analogy for "electron fluid" in a metal conductor. Since electric current is invisible and the processes at play in electronics are often difficult to demonstrate, the various electronic components are represented by hydraulic equivalents. Electricity (as well as heat) was originally understood to be a kind of fluid, and the names of certain electric quantities (such as current) are derived from hydraulic equivalents. As with all analogies, it demands an intuitive and competent understanding of the baseline paradigms (electronics and hydraulics). ==Paradigms== There is no unique paradigm for establishing this analogy. Two paradigms can be used to introduce the concept to students: * Version with pressure induced by gravity. Large tanks of water are held up high, or are filled to differing water levels, and the potential energy of the water head is the pressure source. This is reminiscent of electrical diagrams with an up arrow pointing to +V, grounded pins that otherwise are not shown connecting to anything, and so on. This has the advantage of associating electric potential with gravitational potential. * Completely enclosed version with pumps providing pressure only; no gravity. This is reminiscent of a circuit diagram with a voltage source shown and the wires actually completing a circuit. This paradigm is further discussed below. Other paradigms highlight the similarities between equations governing the flow of fluid and the flow of charge: * Flow and pressure variables can be calculated in both steady and transient fluid flow situations with the use of the hydraulic ohm analogy.〔A. Akers, M. Gassman, & R. Smith, ''Hydraulic Power System Analysis''. Taylor & Francis, New York, 2006, Chapter 13, ISBN 0-8247-9956-9.〕〔A. Esposito, "A Simplified Method for Analyzing Circuits by Analogy". Machine Design, October 1969, pp. 173-177.〕 Hydraulic ohms are the units of hydraulic impedance, which is defined as the ratio of pressure to volume flow rate. The pressure and volume flow variables are treated as phasors in this definition, so possess a phase as well as magnitude.〔Brian J. Kirby, ''Micro- and Nanoscale Fluid Mechanics'', p. 69, Cambridge University Press, 2010 ISBN 1139489836.〕 * A slightly different paradigm is used in acoustics, where acoustic impedance is defined as a relationship between pressure and air speed. In this paradigm, a large cavity with a hole is analogous to a capacitor that stores compressional energy when the time-dependent pressure deviates from atmospheric pressure. A hole (or long tube) is analogous to an inductor that stores kinetic energy associated with the flow of air. 〔Schelleng, John C. "The violin as a circuit." The Journal of the Acoustical Society of America 35.3 (2005): 326-338. http://www.maestronet.com/forum/index.php?app=core&module=attach§ion=attach&attach_id=13435〕 * A circuit was used to model feedback stabilization of a hydrodynamic plasma instability in a magnetic mirror 〔"Axial feedback stabilization of a flute mode in a simple mirror reactor, by M. A. Lieberman and S. L. Wong, Plasma Physics, Vol. 19, pp. 745-55 (1977). The article contains an L-C circuit that is unstable because the "capacitance" is negative: http://iopscience.iop.org/0032-1028/19/8/005/pdf/0032-1028_19_8_005.pdf〕 In this application, the effort was to keep the plasma column centered by applying voltages to the plates, and except for the presence of turbulence and non-linear effects, the plasma was an actual electric circuit element (not really an analog). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「hydraulic analogy」の詳細全文を読む スポンサード リンク
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