Current can be measured by a galvanometer, via the deflection of a magnetic needle in the magnetic field created by the current.

The ampere (SI unit symbol: A), often shortened to amp, is the SI unit of electric current^[1] (quantity symbol: I,i)^[2] and is one of the seven^[3] SI base units. It is named after André-Marie Ampère (1775–1836), French mathematician and physicist, considered the father of electrodynamics. Note that SI supports only the use of symbols and deprecates the use of any abbreviations for units.^[4]

In practical terms, the ampere is a measure of the amount of electric charge passing a point in an electric circuit per unit time with 6.241 × 10¹⁸ electrons, or one coulomb per second constituting one ampere.^[5]

The practical definition may lead to confusion with the definition of a coulomb (i.e., 1 amp-second), but in practical terms this means that measures of a constant current (e.g., the nominal flow of charge per second through a simple circuit) will be defined in amperes (e.g., "a 20 mA circuit") and the flow of charge through a circuit over a period of time will be defined in coulombs (e.g., "a variable-current circuit that flows a total of 10 coulombs over 5 seconds"). In this way, amperes can be viewed as a flow rate, i.e. number of particles (charged) transiting per unit time, and coulombs simply as the number of particles.

Definition[link]

Illustration of the definition of the ampere unit

Ampère's force law^[6][7] states that there is an attractive or repulsive force between two parallel wires carrying an electric current. This force is used in the formal definition of the ampere, which states that it is "the constant current that will produce an attractive force of 2 × 10^–7 newton per metre of length between two straight, parallel conductors of infinite length and negligible circular cross section placed one metre apart in a vacuum".^[1][8]

The SI unit of charge, the coulomb, "is the quantity of electricity carried in 1 second by a current of 1 ampere".^[9] Conversely, a current of one ampere is one coulomb of charge going past a given point per second:

Failed to parse (Missing texvc executable; please see math/README to configure.): \rm 1\ A=1\tfrac C s

That is, in general, charge Q is determined by steady current I flowing for a time t as Q = It.

History[link]

The ampere was originally defined as one tenth of the CGS system electromagnetic unit of current (now known as the abampere), the amount of current that generates a force of two dynes per centimetre of length between two wires one centimetre apart.^[10] The size of the unit was chosen so that the units derived from it in the MKSA system would be conveniently sized.

The "international ampere" was an early realization of the ampere, defined as the current that would deposit 0.001118000 grams of silver per second from a silver nitrate solution.^[11] Later, more accurate measurements revealed that this current is 0.99985 A.

Realization[link]

The standard ampere is most accurately realized using a watt balance, but is in practice maintained via Ohm's Law from the units of electromotive force and resistance, the volt and the ohm, since the latter two can be tied to physical phenomena that are relatively easy to reproduce, the Josephson junction and the quantum Hall effect, respectively.^[12]

At present, techniques to establish the realization of an ampere have a relative uncertainty of approximately a few parts in 10⁷, and involve realizations of the watt, the ohm and the volt.^[12]

Proposed future definition[link]

Rather than a definition in terms of the force between two current-carrying wires, it has been proposed to define the ampere in terms of the rate of flow of elementary charges.^[7] Since a coulomb is approximately equal to 6.2415093×10¹⁸ elementary charges (such as electrons), one ampere is approximately equivalent to 6.2415093×10¹⁸ elementary charges moving past a boundary in one second, or the reciprocal of the value of the elementary charges in coulombs.^[13] The proposed change would define 1 A as being the current in the direction of flow of a particular number of elementary charges per second. In 2005, the International Committee for Weights and Measures (CIPM) agreed to study the proposed change. The new definition is expected to be formally proposed at the 25th General Conference on Weights and Measures (CGPM) in 2014.^[14]

Everyday examples[link]

The current drawn by typical constant-voltage energy distribution systems is usually dictated by the power (watts) consumed by the system and the operating voltage. For this reason the examples given below are grouped by voltage level.

Portable gadgets[link]

• Hearing aid (typically 1 mW at 1.4 V): 0.7 mA

Motor vehicles – 12 V DC[link]

A typical motor vehicle has a 12 V battery. The various accessories that are powered by the battery might include:

• Instrument panel light (typically 2 W): 166 mA.
• Headlights (typically 60 W): 5 A each.
• Starter Motor (typically 1–2 kW): 80-160 A

North American domestic supply – 120 V AC[link]

Most United States, Canada and Mexico domestic power suppliers run at 120 V.

Household circuit breakers typically provide a maximum of 15 A or 20 A of current to a given set of outlets.

• 22-inch/56-centimeter portable television (35 W): 290 mA
• Tungsten light bulb (60–100 W): 500–830 mA
• Toaster, kettle (2 kW): 16.6 A
• Immersion heater (4.6 kW): 38.3 A

European domestic supply – 230 V AC[link]

Most European domestic power supplies run at 230 V, so the current drawn by a particular European appliance (in Europe) will be less than for an equivalent American one (in the United States).^{[Note 1]}

The current drawn by a number of typical appliances are:

• 22-inch/56-centimeter Portable Television (35 W): 150 mA
• Tungsten light bulb (60–100 W): 250–450 mA
• Toaster, kettle (2 kW): 9 A
• Immersion heater (4.6 kW): 20 A

See also[link]

• Ammeter
• Ampacity (current-carrying capacity)
• Electric current
• Electric shock
• Hydraulic analogy
• Magnetic constant

Notes[link]

References[link]

External links[link]

• The NIST Reference on Constants, Units, and Uncertainty
• A short history of the SI units in electricity^{[dead link]}
• NIST Definition of ampere and μ₀

v t e SI units Base units Ampere · Candela · Kelvin · Kilogram · Metre · Mole · Second Derived units Becquerel · Coulomb · Degree Celsius · Farad · Gray · Henry · Hertz · Joule · Katal · Lumen · Lux · Newton · Ohm · Pascal · Radian · Siemens · Sievert · Steradian · Tesla · Volt · Watt · Weber Accepted for use with SI Dalton (Atomic mass unit) · Astronomical unit · Day · Decibel · Degree Celsius · Degree of arc · Electronvolt · Hectare · Hour · Litre · Minute · Minute of arc · Neper · Second of arc · Tonne Atomic units · Natural units See also SI prefixes · Systems of measurement · Conversion of units · New SI definitions · History of the metric system Book:International System of Units  · Category:SI base units

André-Marie Ampère
André-Marie Ampère (1775-1836)
Born	(1775-01-20)20 January 1775 Parish of St. Nizier, Lyon, France
Died	10 June 1836(1836-06-10) (aged 61) Marseille, France
Residence	France
Nationality	French
Fields	Physics
Institutions	Bourg-en-Bresse École Polytechnique
Known for	Ampere's Law
Signature

André-Marie Ampère (20 January 1775 – 10 June 1836) was a French physicist and mathematician who is generally regarded as one of the main discoverers of electromagnetism. The SI unit of measurement of electric current, the ampere, is named after him.

Early days[link]

Ampère was born in Lyon, France on 20 January 1775. He spent his childhood and adolescence at the family property at Poleymieux-au-Mont-d'Or near Lyon.^[1] His father began to teach him Latin, until he discovered the boy's preference and aptitude for mathematical studies. The young Ampère, however, soon resumed his Latin lessons, to enable him to master the works of Euler and Bernoulli. In later life Ampère claimed that he knew as much about mathematics and science when he was eighteen as ever he knew; but, a polymath, his reading embraced history, travels, poetry, philosophy, and the natural sciences.

During the French Revolution, Ampere's father stayed at Lyon expecting to be safer there. Nevertheless, after the revolutionaries had taken the city he was captured and executed. This death was a great shock to Ampère.

In 1796 Ampère met Julie Carron, and in 1799 they were married. From about 1796, Ampère gave private lessons at Lyon in mathematics, chemistry, and languages. In 1801 he moved to Bourg-en-Bresse, as professor of physics and chemistry, leaving his ailing wife and his infant son (Jean-Jacques Ampère) at Lyon. Her death, in July 1803, troubled Ampère for the rest of his life. Also in 1804, Ampère was appointed professor of mathematics at the University of Lyon.

Ampère claimed that "at eighteen years he found three culminating points in his life, his First Communion, the reading of Antoine Leonard Thomas's "Eulogy of Descartes", and the Taking of the Bastille. On the day of his wife's death he wrote two verses from the Psalms, and the prayer, 'O Lord, God of Mercy, unite me in Heaven with those whom you have permitted me to love on earth.' Serious doubts harassed him at times, and made him very unhappy. Then he would take refuge in the reading of the Bible and the Fathers of the Church."^[2]

For a time he took into his family the young student Antoine-Frédéric Ozanam (1813–1853), one of the founders of the Conference of Charity, later known as the Society of Saint Vincent de Paul. Through Ampère, Ozanam had contact with leaders of the neo-Catholic movement, such as François-René de Chateaubriand, Jean-Baptiste Henri Lacordaire, and Charles Forbes René de Montalembert. Ozanam was beatified by Pope John Paul II in 1997.

Physics and further studies[link]

Jean Baptiste Joseph Delambre's recommendation obtained for Ampère the Lyon appointment, and afterwards (1805) a minor position in the polytechnic school at Paris, where he was appointed professor of mathematics in 1809. Here Ampère continued to pursue his scientific research and his diverse studies with unabated diligence. He was admitted as a member of the Institute in 1814.

Ampère's fame mainly rests on his establishing the relations between electricity and magnetism, and in developing the science of electromagnetism, or, as he called it, electrodynamics. On 11 September 1820 he heard of H. C. Ørsted's discovery that a magnetic needle is acted on by a voltaic current. Only a week later, on 18 September, Ampère presented a paper to the Academy containing a much more complete exposition of that and kindred phenomena. On the same day, Ampère also demonstrated before the Academy that parallel wires carrying currents attract or repel each other, depending on whether currents are in the same (attraction) or in opposite directions (repulsion). This laid the foundation of electrodynamics.

The topic of electromagnetism thus begun, Ampère developed a mathematical theory which not only described the electromagnetic phenomena already observed, but also predicted many new ones.

In 1827 he was elected a Foreign Member of the Royal Society and in 1828, a foreign member of the Royal Swedish Academy of Science.^[3]

Writings[link]

• Considerations sur la théorie mathématique du jeu, Perisse, Lyon Paris 1802, online lesen im Internet-Archiv
• André-Marie Ampère: Recueil d'observations électro-dynamiques. contenant divers mémoires, notices, extraits de lettres ou d'ouvrages périodiques sur les sciences, relatifs a l'action mutuelle de deux courans électriques, à celle qui existe entre un courant électrique et un aimant ou le globe terrestre, et à celle de deux aimans l'un sur l'autre Chez Crochard, 1822 (read online at Google Books; as at: 2010-9-26). 
• André-Marie Ampère, Babinet (Jacques, M.): Exposé des nouvelles découvertes sur l'électricité et le magneétisme. Chez Méquignon-Marvis, 1822 (read online at Google Books; as at: 2010-9-26). 
• André-Marie Ampère: Description d'un appareil électro-dynamique. Chez Crochard … et Bachelie, 1824 (read online at Google Books; as at: 2010-9-26). 
• André-Marie Ampère: Théorie des phénomènes électro-dynamiques, uniquement déduite de l'expérience. Méquignon-Marvis, 1826 (read online at Google Books; as at: 2010-9-26). 
  • André-Marie Ampère: Théorie mathématique des phénomènes électro-dynamiques: uniquement déduite de l'expérience. A. Hermann, 1883 (Neuauflage) (online lesen im Internet-Archiv; as at: 2010-9-26). 
• André-Marie Ampère: Essai sur la philosophie des sciences, ou, Exposition analytique d'une classification naturelle de toutes les connaissances humaines. Chez Bachelier, 1834 (read online at Google Books; as at: 2010-9-26). 
  • André-Marie Ampère: Essai sur la philosophie des sciences. Bd. 1, Chez Bachelier, 1834 (read online at Google Books; as at: 2010-9-26). 
  • André-Marie Ampère: Essai sur la philosophie des sciences. Bd. 2, Bachelier, 1843 (read online at Google Books; as at: 2010-9-26). 

Last years[link]

Grave of Ampère and his son

Ampère died at Marseille and was buried in the Cimetière de Montmartre, Paris. The great amiability and childlike simplicity of his character are well brought out in his Journal et correspondence (Paris, 1872).

Ampère's final work, published posthumously, was Essai sur la philosophie des sciences, ou exposition analytique d'une classification naturelle de toutes les connaissances humaines ("Essay on the philosophy of science or analytical exposition on the natural classification of human knowledge").

References[link]

Williams, L. Pearce (1970). "Ampère, André-Marie". Dictionary of Scientific Biography. 1. New York: Charles Scribner's Sons. pp. 139–147. ISBN 0-684-10114-9. 

External links[link]

Wikimedia Commons has media related to: André-Marie Ampère

Wikisource has the text of the 1911 Encyclopædia Britannica article Ampère, André Marie.

Wikiquote has a collection of quotations related to: André-Marie Ampère

• Ampère and the history of electricity - a French-language, edited by CNRS, site with Ampère's correspondence (full text and critical edition with links to manuscripts pictures, more than 1000 letters), an Ampère bibliography, experiments, and 3D simulations
• Ampère Museum - a French-language site from the museum in Poleymieux-au-Mont-d'or, near Lyon, France
• O'Connor, John J.; Robertson, Edmund F., "André-Marie Ampère", MacTutor History of Mathematics archive, University of St Andrews, http://www-history.mcs.st-andrews.ac.uk/Biographies/Ampere.html .
• Weisstein, Eric W., Ampère, André (1775-1836) from ScienceWorld.
• Catholic Encyclopedia on André Marie Ampère

•  This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). Encyclopædia Britannica (11th ed.). Cambridge University Press. 
• André-Marie Ampère: The Founder of Electromagnetism - Background information and related experiments

This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (March 2008)

André Marie (3 December 1897 Honfleur, Calvados  – 12 June 1974 Rouen) was a French Radical politician who served as Prime Minister during the Fourth Republic in 1948.

Biography[link]

Born at Honfleur in 1897, the young André Marie studied at primary and secondary level there, going on to the Lycée Pierre Corneille,^[1] when his parents moved to Rouen in 1908. While preparing to apply to the École Normale Supérieure Lettres et Sciences Humaines, he was mobilised at the end of 1916. By the end of World War I, he commanded a battery of 75 men. He received two light injuries and numerous commendations. He was decorated with the Croix de guerre with palm.

He started work as a lawyer in 1922. He was elected Deputy for Seine-Inférieure (now Seine-Maritime), holding his seat in the Palais Bourbon from 1928 to 1962. In 1933, André Marie entered the government as Under-Secretary of State to Albert Sarraut, responsible for Alsace-Lorraine. He served in several Under-Secretarial posts, and represented France at the League of Nations.

As World War II escalated, André Marie, a reserve captain, was one of several parliamentarians who enlisted voluntarily. An artillery captain, he was decorated with a second croix de guerre, taken prisoner, and imprisoned at the Oflag at Saarburg. He was therefore absent for the vote of 10 July 1940, which empowered Marshal Pétain and instituted the regime of Vichy France.

Marie was freed in 1941, having served as an officer in both World Wars. Refusing Vichy politics on his return to Seine-Maritime, he resigned all his elected offices, and in a letter to his constituents, expained that he could not exercise his mandate while the people could not be consulted freely. As a member of the Georges-France resistance network, he was denounced and arrested on 12 September 1943 by occupation authorities, imprisoned at Compiègne, then deported to a camp at Buchenwald on 16 December 1943, where he remained until the liberation of the camp by American troops on 11 April 1945. He had lost 30 kilograms, and had suffered a heart infection and a liver infection.

On his return to France, André Marie quickly regained his place in political life, both at departmental and national levels.

In 1947, he was appointed Minister of Justice in the Ramadier ministry, and presided over the last trials in the High Court of collaborators. The President called on him to become Prime Minister, replacing Robert Schuman on 27 July 1948, but he was obliged to resign a month later.

He accepted the post of Deputy Prime Minister in the Queuille cabinet in 1948, and was again named Minister of Justice, refusing to pursue the Communists after the miners' strikes of 1948. On 3 February 1949, as Minister of Justice, he was called to account in the National Assembly on the matter of the economic collaborator Pierre Brice. The radical Deputy Emmanuel d'Astier de la Vigerie declared: "Men who have amassed fortunes as a result of collaboration are now largely free to enjoy the fruits of their treason because the government, indulgent towards collaborators, has led a politic of repression against the working class." Weakened by the affair, André Marie resigned on 13 February 1949.

He then served as Minister of Education, from August 1951 until June 1954. Il brought about the Marie and Barangé laws, in support of free education. An ardent proponent of public education, he brought about the law, still in place, which makes students of the écoles normales supérieures trainee civil servants: in exchange for a monthly salary, they may be asked to serve the government at any point during the ten years following their matriculation.

Mayor of Barentin from 1945 to 1974, he installed the statues of the town's famous "street museum".

Ministry (26 July - 5 September 1948)[link]

• André Marie - President of the Council
• Pierre-Henri Teitgen - Vice President of the Council
• Léon Blum - Vice President of the Council
• Robert Schuman - Minister of Foreign Affairs
• René Mayer - Minister of National Defense
• Jules Moch - Minister of the Interior
• Paul Reynaud - Minister of Finance and Economic Affairs
• Robert Lacoste - Minister of Commerce and Industry
• Daniel Mayer - Minister of Labour and Social Security
• Robert Lecourt - Minister of Justice
• Yvon Delbos - Minister of National Education
• André Maroselli - Minister of Veterans and War Victims
• Pierre Pflimlin - Minister of Agriculture
• Paul Coste-Floret - Minister of Overseas France
• Christian Pineau - Minister of Public Works and Transport
• Pierre Schneiter - Minister of Public Health and Population
• René Coty - Minister of Reconstruction and Town Planning
• Henri Queuille - Minister of State
• Paul Ramadier - Minister of State

References[link]

v t e Heads of government of France Restoration Talleyrand Richelieu Dessolles Decazes Richelieu Villèle Martignac Polignac July Monarchy V. de Broglie Laffitte Perier Soult Gérard Maret Mortier V. de Broglie Thiers Molé Soult Thiers Soult Guizot Molé Second Republic Dupont de l'Eure Arago Cavaignac Barrot Hautpoul Faucher Second Empire Ollivier Cousin-Montauban Interregnum Trochu Third Republic Dufaure A. de Broglie Cissey Buffet Dufaure Simon A. de Broglie Rochebouët Dufaure Waddington Freycinet Ferry Gambetta Freycinet Duclerc Fallières Ferry Brisson Freycinet Goblet Rouvier Floquet Tirard Freycinet Loubet Ribot Dupuy Casimir-Perier Dupuy Ribot Bourgeois Méline Brisson Dupuy Waldeck-Rousseau Combes Rouvier Sarrien Clemenceau Briand Monis Caillaux Poincaré Briand Barthou Doumergue Ribot Viviani Briand Ribot Painlevé Clemenceau Millerand Leygues Briand Poincaré François-Marsal Herriot Painlevé Briand Herriot Poincaré Briand Tardieu Chautemps Tardieu Steeg Laval Tardieu Herriot Paul-Boncour Daladier Sarraut Chautemps Daladier Doumergue Flandin Bouisson Laval Sarraut Blum Chautemps Blum Daladier Reynaud Pétain Vichy France Pétain Laval Brinon Provisional Government de Gaulle Gouin Bidault Auriol Blum Fourth Republic Ramadier Schuman Marie Schuman Queuille Bidault Queuille Pleven Queuille Pleven Faure Pinay Mayer Laniel Mendès France Faure Mollet Bourgès-Maunoury Gaillard Pflimlin de Gaulle Fifth Republic de Gaulle Debré Pompidou Couve de Murville Chaban-Delmas Messmer Chirac Barre Mauroy Fabius Chirac Rocard Cresson Bérégovoy Balladur Juppé Jospin Raffarin de Villepin Fillon Ayrault Italics indicates interim holder