arc

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.

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.

Long, curved chain of oceanic islands associated with intense volcanic and seismic activity and mountain-building processes. Examples include the Aleutian-Alaska Arc and the Kuril-Kamchatka Arc. Most island arcs consist of two parallel rows of islands. The inner row is a string of volcanoes, and the outer row is made up of nonvolcanic islands. In the case of single arcs, many of the islands are volcanically active. An island arc typically has a landmass or a partially enclosed, unusually shallow sea on its concave side. Along the convex side there usually exists a long, narrow deep-sea trench.

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Type of electric furnace in which heat is generated by an arc between carbon electrodes above the surface of the material (commonly a metal) being heated. William Siemens first demonstrated the arc furnace in 1879 at the Paris Exposition by melting iron in crucibles; horizontally placed carbon electrodes produced an electric arc above the container of metal. The first commercial arc furnace in the U.S. (1906) had a capacity of four tons (3.6 metric tons) and was equipped with two electrodes. Modern furnaces range in heat size from a few tons up to 400 tons (360 metric tons), and the arcs strike directly into the metal bath from vertically positioned, graphite electrodes to remelt scrap steel or refine briquettes of direct-reduced iron ore.

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French Jeanne d'Arc

(born circa 1412, Domrémy, Bar, Fr.—died May 30, 1431, Rouen; canonized May 16, 1920; feast day May 30) French military heroine. She was a peasant girl who from an early age believed she heard the voices of Sts. Michael, Catherine, and Margaret. When she was about 16, her voices began urging her to aid France's Dauphin (crown prince) and save France from the English attempt at conquest in the Hundred Years' War. Dressed in men's clothes, she visited the Dauphin and convinced him, his advisers, and the church authorities to support her. With her inspiring conviction, she rallied the French troops and raised the English siege of Orléans in 1429. She soon defeated the English again at Patay. The Dauphin was crowned king at Reims as Charles VII, with Joan beside him. Her siege of Paris was unsuccessful, and in 1430 she was captured by the Burgundians and sold to the English. Abandoned by Charles, she was turned over to the ecclesiastical court at Rouen, controlled by French clerics who supported the English, and tried for witchcraft and heresy (1431). She fiercely defended herself but finally recanted and was sentenced to life imprisonment; when she again asserted that she had been divinely inspired, she was burned at the stake. She was not canonized until 1920.

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French Jeanne d'Arc

(born circa 1412, Domrémy, Bar, Fr.—died May 30, 1431, Rouen; canonized May 16, 1920; feast day May 30) French military heroine. She was a peasant girl who from an early age believed she heard the voices of Sts. Michael, Catherine, and Margaret. When she was about 16, her voices began urging her to aid France's Dauphin (crown prince) and save France from the English attempt at conquest in the Hundred Years' War. Dressed in men's clothes, she visited the Dauphin and convinced him, his advisers, and the church authorities to support her. With her inspiring conviction, she rallied the French troops and raised the English siege of Orléans in 1429. She soon defeated the English again at Patay. The Dauphin was crowned king at Reims as Charles VII, with Joan beside him. Her siege of Paris was unsuccessful, and in 1430 she was captured by the Burgundians and sold to the English. Abandoned by Charles, she was turned over to the ecclesiastical court at Rouen, controlled by French clerics who supported the English, and tried for witchcraft and heresy (1431). She fiercely defended herself but finally recanted and was sentenced to life imprisonment; when she again asserted that she had been divinely inspired, she was burned at the stake. She was not canonized until 1920.

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Arc may refer to:

Computing and gaming

• Arc (programming language), a Lisp dialect in development by Paul Graham
• .arc, a file extension for archive files
• arc, the command-line interface for ArcInfo
• Arc System Works, a video game developer

Engineering

• Arc chute, a protective device in an electrical circuit breaker
• Arc lamp, a device that produces light by an electric arc
• Arc welding, a method of welding that uses an electric arc to melt the metals together
• Electric arc or voltaic arc, an ongoing plasma discharge (an electric current through a gas), producing light and heat
• Arc or arch, a bowed or curved structure capable of spanning a space while supporting significant weight

Geography

• Arc (Savoie), a river of eastern France, tributary of the Isère river
• Arc (Provence), a river of southern France, flowing into the Étang de Berre
• Les Arcs, a ski resort in the French Alps
• Volcanic arc or island arc, a chain of volcanic mountains or islands formed by plate tectonics
• Arc of the United States, a charitable organization
• An arts centre in Stockton-on-Tees, County Durham, England

Modern culture

• Story arc, an extended or continuing storyline
• Character arc, the status of a character as it unfolds throughout the story
• "Arc" (song), a song by Pearl Jam
• Arc (album), a live album by Neil Young

Mathematics

• Arc (geometry), a segment of a differentiable curve
• Arc (projective geometry), a particular type of set of points of a projective plane
• Arcminute, a measure used for angles, equal to 1/60th of a degree
• "arc-", a prefix sometimes used for an inverse function, specifically trigonometry functions
• A directed edge in graph theory

Optics

• 120° parhelion, relatively rare halo, an optical phenomenon occasionally appearing along with very bright sun dogs
• Infralateral arc, a rare halo, an optical phenomenon appearing similar to a rainbow under a white parhelic circle
• Lower tangent arc, rarely observable halo, an optical phenomenon appearing under and tangent to a 22° halo centred around the sun
• Parry arc, a rare halo, an optical phenomenon which occasionally appears over a 22° halo together with a upper tangent arc
• Subhelic arc, a rare halo that curves upwards from the horizon and touches the tricker arc above the anthelic point
• Supralateral arc, a rare halo, an optical phenomenon often confused with the indeed infrequently appearing 46° halo
• Upper tangent arc, halo, an atmospheric optical phenomenon which appears over and tangent to the 22° halo centred around the sun

Other

• Aramaic language (ISO 639-2/3 language code), a Semitic language
• Joan of Arc
• Prix de l'Arc de Triomphe, a Group 1 flat horse race
• The Arc (Bahá'í), a number of administrative buildings for the Bahá'í Faith, located on Mount Carmel in Israel

See also

• Ark
• Arch
• ARCS