Longman Dictionary of Contemporary English
The Collaborative International Dictionary
electric current \electric current\, electrical current \electrical current\, the movement of electrically charged particles, atoms, or ions, through solids, liquids, gases, or free space; the term is usually used of relatively smooth movements of electric charge through conductors, whether constant or variable. Sudden movements of charge are usually referred to by other terms, such as spark or lightning or discharge. In metallic conductors the electric current is usually due to movement of electrons through the metal. The current is measured as the rate of movement of charge per unit time, and is counted in units of amperes. As a formal definition, the direction of movement of electric current is considered as the same as the direction of movement of positive charge, or in a direction opposite to the movement of negative charge. Electric current may move constantly in a single direction, called direct current (abbreviated DC), or may move alternately in one direction and then the opposite direction, called alternating current (abbreviated AC).
alt. 1 an electric circuit in which voltage and current do not vary with time 2 an electric current in which the electrons flow in one direction, but may vary with time n. 1 an electric circuit in which voltage and current do not vary with time 2 an electric current in which the electrons flow in one direction, but may vary with time
n. an electric current that flows in one direction steadily [syn: DC] [ant: alternating current]
Direct current (DC) is the unidirectional flow of electric charge. Direct current is produced by sources such as batteries, power supplies, thermocouples, solar cells, or dynamos. Direct current may flow in a conductor such as a wire, but can also flow through semiconductors, insulators, or even through a vacuum as in electron or ion beams. The electric current flows in a constant direction, distinguishing it from alternating current (AC). A term formerly used for this type of current was galvanic current.
The abbreviations AC and DC are often used to mean simply alternating and direct, as when they modify current or voltage.
Direct current may be obtained from an alternating current supply by use of a rectifier, which contains electronic elements (usually) or electromechanical elements (historically) that allow current to flow only in one direction. Direct current may be converted into alternating current with an inverter or a motor-generator set.
Direct current is used to charge batteries and as power supply for electronic systems. Very large quantities of direct-current power are used in production of aluminum and other electrochemical processes. It is also used for some railways, especially in urban areas. High-voltage direct current is used to transmit large amounts of power from remote generation sites or to interconnect alternating current power grids.