James Prescott Joule

James Prescott Joule [ dʒu ː l] ( born December 24, 1818 in Salford, near Manchester, † October 11, 1889 in Sale (Greater Manchester ) ) was a British physicist.

Life and work

Joule was the third son of a brewer. Later took over and he ran this brewery with his brother. From 1834 joules studied with John Dalton mathematics and science. In 1837 he established himself a chemical laboratory, which was supported later by various clubs. Soon he married, but his spouse died already 1854. 1847 began working with William Thomson, 1st Baron Kelvin. From 1872 he was plagued by health problems. When he came in later years in financial difficulties, the British Queen Victoria granted him a pension from 1878.

Started in 1838 joules based on the works of William Sturgeon with electromagnetic experiments that he gave up because of thermodynamics. From 1840 he devoted himself to studies on the thermal effects of the current. He noticed the heating of the current carrying conductor ( Joule heat ). Also in 1840, he formulated the Joule's law, according to which the heat is proportional to the product of the square of the current and the resistance of the circuit.

In the following years he measured the heat development during various operations. He suspected the existence of an early equivalence of mechanical work and heat (mechanical equivalent of heat ) and resulted in a classic 1843 and named after him trying out: One of thermally insulated water amount was fed a defined amount of mechanical energy and then measured the temperature increase. In this way he was able to prove the existence of a heat equivalence, which is measured in his honor in the unit joules. This evidence provided in 1841 already Heilbronner doctor Robert Mayer ( 1814-1878 ), the so found, however, no recognition.

Discovered in 1846 joules to the change in length of magnetized ferromagnetic material, the magnetostriction ( Joule effect ), which has found application for the generation of ultrasonic waves. In 1852, Joule worked with Thomson in experiments to confirm thermodynamic theories. 1852 showed the two researchers that a gas can expand undisturbed, to cool down. This Joule- Thomson effect was a proof of the assumption that weak forces acting between the gas molecules. Application was the sentence in gas liquefaction and refrigeration. In addition, designed the Joule ideal cyclic process of hot air machine ( Joule process ).

Honors

From 1850 Joule was a member of the Royal Society, which honored him in 1852 with the Royal Medal, 1870, the Copley Medal. In his honor, called the SI unit of energy, work and heat " joule " ( unit symbol J).

Works

• New theory of heat, 1850