Charles Augustin Coulomb | Biography

Charles-Augustin Coulomb was born at Angoulême, Charente, France, on June 14, 1736. He was educated as a military engineer, and graduated from the Ecole du Génie in 1761. He served at various posts, and ended up at Paris in 1776.

An interest in magnetism induced Coulomb to enter a competition sponsored by the Paris Academy of Science in 1777. He shared first prize for his paper on magnetic compasses and, in 1781, he received a double first prize for his work on friction. These honors helped get him elected to the Academy.

While Coulomb had been experimenting with compasses, he noticed slight errors were introduced by friction acting on the pivot that held the magnetized needle. He invented a compass that had its needle suspended by a fine thread. The thread was an improvement, but it twisted. Coulomb realized that the amount of twisting was related to the amount of force the Earth's magnetic field applied to the needle. This realization led him to the invention of the torsion balance in 1777. (English geologist John Michell had actually anticipated Coulomb, devising a torsion balance around the year 1750.)

The torsion balance allowed Coulomb to measure extremely small weights. With it, he was able to measure the force acting upon two electrically charged balls, discovering that the force changed as the distance between the balls varied. In 1785 Coulomb issued what would become known as Coulomb's Law, which states that the repulsion and attraction of two electrically charged objects depends on the product of their charges and the inverse square of the distance between them. This "inverse-square" law was very similar to the law of gravity discovered by Isaac Newton. Once again, Coulomb had been anticipated; Henry Cavendish had independently discovered "Coulomb's Law," but neglected to publish his work. Cavendish's work didn 't come to light until fifty years after his death.

Coulomb investigated static electrical charges and discovered they adhered to the same inverse-square law as magnetic forces. This established a relationship between electric and magnetic forces that led André Ampère to discover the link between magnetism and electric current. Coulomb also found that the electric charges were located on the surface of a charged body and not within its center.

The French Revolution erupted in 1789 and Coulomb left Paris. Two years later, Coulomb decided it would be wise to resign his military commission. After the Revolution he was restored to his former posts and returned to Paris, where he eventually died on August 23, 1806. In the years between 1781 and 1806 he had published twenty-five papers dealing with magnetism, electricity, and the torsion balance. In his honor the unit of electric charge is named the coulomb.