Ampere, Andre-Marie (physicist)


(1775-1836) French Theoretical and Experimental Physicist (Electrodynamics), Mathematical Physicist

Andre-Marie Ampere founded a new branch of physics that he named electrodynamics: the study of the relationship between mechanical forces and electric and magnetic forces. In his honor the unit of electric current is called the ampere or amp.

He was born in Polemieux, near Lyons, France, on January 22, 1775. The man who would later teach physics, mathematics, and chemistry had no formal education. Ampere’s father was a wealthy merchant, who, in addition to having his son privately tutored, was personally involved in his education and inspired in him a passionate desire to learn. Ampere’s caring and protective family imbued in him both an optimistic belief in the fruits of scientific investigation, which was characteristic of the Enlightenment, and a devotion to Catholicism. He was apparently something of a prodigy, mastering mathematical texts independently, at an early age.

When he was 18, however, his peaceful world of study and family affection was shattered by the advent of the French Revolution. In 1793, Lyons was captured by the Republican Army, and his beloved father, who was a wealthy city official, was guillotined. A devastated Andre-Marie put down his books on mathematics and would not return to them for 18 months. When he met his future wife, Julie, he began to come to life again.

In 1802 Ampere published his first treatise, The Mathematical Theory of Games, an early contribution to probability theory, and was appointed professor of physics and chemistry at the Ecole Centrale in Bourg. Later that year, he became professor of mathematics at the Lycee in Lyons. Ampere’s career was thriving, but another of the personal tragedies that would haunt his life was about to occur: his young wife, whose health had been steadily declining, died in 1804. The grieving Ampere left Lyon with its sad memories for the intellectual excitement of Paris.

He quickly found a position as an assistant lecturer in mathematical analysis at the Ecole Polytechnique in Paris, and, four years later, he was promoted to professor of mathematics. Once more his personal life formed a dark counterpoint to his professional activities. He remarried in August 1806 but had already separated from his second wife by the time their daughter was born 11 months later. Meanwhile, his talent had been recognized by Napoleon, who in 1808 appointed him inspector-general of the newly formed university system, a post he held until his death. He also taught philosophy at the University of Paris in 1918, became assistant professor of astronomy in 1920, and was appointed to the chair of experimental physics at the College de France in 1824.

Ampere’s intellectual voracity and versatility continued unabated; between 1805 and his famous work on electrodynamics in the 1820s, he studied psychology, philosophy, physics, and chemistry. In 1820, the Danish physicist hans christian 0rsted demonstrated his discovery that a magnetic needle is deflected when the current in a nearby wire is flowing, thereby showing evidence of a relationship between electricity and magnetism. Ampere witnessed a restaging of 0rsted’s demonstration in Paris that same year. Within a week he had prepared the first of several papers that would describe a new branch of physics revealed by 0rsted’s work. Ampere called it electrodynamics, to differentiate it from the electrostatics of charles augustin coulomb. Central to his thinking was a relationship that came to be known as Ampere’s law, a mathematical description of the magnetic force between two electric currents. It shows that two parallel wires carrying electric currents in the same direction attract each other, whereas two parallel wires carrying electric currents in opposite directions repel one another. Specifically, Ampere’s law relates the magnetic force produced by two parallel current-carrying conductors to the product of their currents divided by the square of the distance between the conductors. Today, Ampere’s law is usually stated in the form of calculus: the line integral of the magnetic field around an arbitrarily chosen path is proportional to the net electric current enclosed by the path.

Ampere also predicted and demonstrated that a helical “coil” of wire (which he named a solenoid) behaves as a bar magnet when carrying an electric current. The numerous experiments he performed enabled him to explain known electromagnetic phenomena and predict new ones. In addition, Ampere pioneered the development of measuring techniques for electricity, inventing an instrument using a free-moving needle to measure the strength of the current. This was the prototype of what we know today as the galvanometer.

He also tried to develop a theory to explain electromagnetism, proposing that magnetism is merely electricity in motion. Prompted by his close friend augustus fresnel, one of the originators of the wave theory of light, he suggested that molecules are surrounded by a perpetual electric current.

Ampere culminated his groundbreaking studies with the publication in 1827 of his Memoir on the Mathematical Theory of Electro-dynamic Phenomena, Uniquely Deduced from Experience, in which he enunciated precise mathematical formulations of electrodynamics, notably Ampere’s law.

He died of pneumonia at the age of 61, on June 10, 1836, while on an inspection tour of Marseille. The epitaph on his gravestone reads, Tandem felix (Happy at last).

Ampere was honored by election as a fellow of the Royal Society in 1827. His name is inscribed, along with those of 71 other prominent French scientists, on the Eiffel Tower. The Rue Ampere, a street in the 17 tharrondisement in Paris, and the Mons Ampere, a feature of the lunar landscape, have been named for him.

More than any other scientist, Ampere was responsible for creating the discipline of electrodynamics. Decades later Ampere’s law became an integral part of james clerk maxwell’s unified theory of electrodynamics.

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