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An electric current is a flow of electric charge. In electric circuits this charge is often carried by moving electrons in a wire. It can also be carried by ions in an electrolyte, or by both ions and electrons such as in a plasma. The SI unit for measuring an electric current is the ampere, which is the flow of electric charge across a surface at the rate of one coulomb per second. Electric current is measured using a device called an ammeter. Electric currents cause Joule heating, which creates light in incandescent light bulbs. They also create magnetic fields, which are used in motors, inductors and generators. The particles that carry the charge in an electric current are called charge carriers. In metals, one or more electrons from each atom are loosely bound to the atom, and can move freely about within the metal. These conduction electrons are the charge carriers in metal conductors. ==Symbol== The conventional symbol for current is , which originates from the French phrase ''intensité de courant'', meaning ''current intensity''.〔T. L. Lowe, John Rounce, ''Calculations for A-level Physics'', p. 2, Nelson Thornes, 2002 ISBN 0-7487-6748-7.〕〔Howard M. Berlin, Frank C. Getz, ''Principles of Electronic Instrumentation and Measurement'', p. 37, Merrill Pub. Co., 1988 ISBN 0-675-20449-6.〕 Current intensity is often referred to simply as ''current''.〔K. S. Suresh Kumar, ''Electric Circuit Analysis'', Pearson Education India, 2013, ISBN 9332514100, section 1.2.3 "'Current intensity' is usually referred to as 'current' itself."〕 The symbol was used by André-Marie Ampère, after whom the unit of electric current is named, in formulating the eponymous Ampère's force law, which he discovered in 1820.〔A-M Ampère, (''Recuil d'Observations Électro-dynamiques'' ), p. 56, Paris: Chez Crochard Libraire 1822 (in French).〕 The notation travelled from France to Great Britain, where it became standard, although at least one journal did not change from using to until 1896.〔(''Electric Power'' ), vol. 6, p. 411, 1894.〕 == Conventions == In metals, which make up the wires and other conductors in most electrical circuits, the positively charged atomic nuclei are held in a fixed position, and the electrons are free to move, carrying their charge from one place to another. In other materials, notably the semiconductors, the charge carriers can be positive ''or'' negative, depending on the dopant used. Positive and negative charge carriers may even be present at the same time, as happens in an electrochemical cell. A flow of positive charges gives the same electric current, and has the same effect in a circuit, as an equal flow of negative charges in the opposite direction. Since current can be the flow of either positive or negative charges, or both, a convention is needed for the direction of current that is independent of the type of charge carriers. The direction of ''conventional current'' is arbitrarily defined as the same direction as positive charges flow. The consequence of this convention is that electrons, the charge carriers in metal wires and most other parts of electric circuits, flow in the opposite direction of conventional current flow in an electrical circuit. 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「electric current」の詳細全文を読む スポンサード リンク
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