arc

arc, in electricity

arc, in electricity, highly luminous and intensely hot discharge of electricity between two electrodes. The arc was discovered early in the 19th cent. by the English scientist Sir Humphry Davy, who so named it because of its shape. An arc is characterized by a high current, low voltage, and indefinite duration. It is usually started when two electrodes carrying an electric current are drawn apart. At the instant the electrodes are parted, strong electric forces draw electrons from one electrode to the other, initiating the arc. The discharge consists of a current composed of these electrons and charged gas particles, called ions, that form between the electrodes. The first practical electric light, the arc lamp, made use of the arc formed between two carbon rods (see lighting). Today the use of the arc lamp is limited to special purposes, e.g., in searchlights and in research applications. The principle of the electric arc is employed in welding (as in the hydrogen arc, where hydrogen is introduced between tungsten electrodes) and also in generating heat in the electric furnace. A spark, like an arc, is a discharge of electricity between two points, but it has a high voltage and a short duration. Lightning is an example of a spark.

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arc, in geometry

arc, in geometry, a curved line or any part of it; in particular, a portion of the circumference of a circle. The length s of an arc of a circle of radius r and subtending a central angle of θ radians is s=rθ; if θ is measured in degrees, then the arc is given by s=2πrθ/360.

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(1) PC compression programs from System Enhancement Associates, Inc., Clifton, NJ. ARC was one of the first compression utilities to become popular in the early 1980s. ARC+Plus provides enhanced features and speed.

(2) The ARC extension was previously used by PKWARE Inc. in its PKARC program.

(3) (Advanced RISC Computing) An earlier open system specification based on the MIPS R3000 and R4000 CPUs. It included EISA and TURBOchannel buses.

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1.		ARC - Advanced RISC Computing Specification
2.	(file format, tool)	arc - An old archive format for IBM PC. The format is now so obscure that it is only likely to be supported by jack-of-all-trades decompression programs such as WINZIP.
3.	(mathematics, data)	arc - An edge in a tree. "branch" is a generally more common synonym.