# James Prescott Joule

Essay by lil_azn77Junior High, 9th grade April 2006

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James Prescott Joule (December 24, 1818 - October 11, 1889) was a British physicist who was born in Salford, England. In 1833, he was sent by his father to be tutored for four years by the famous scientist John Dalton. Joule soon became one of the most accurate scientists of his time. During 1838 - 1841 when he was working in his father's brewery, he tried to make a much more efficient motor. At just 20 years of age, after sending a numerous amount of papers to 'Annals of Electricity', one of his letters was finally published. It stated that Joule found that

in an electromagnetic machine, bundles of iron worked much more efficiently than a solid core magnet.

In early 1839, Joule discovered a law which describes the relationship between currents and electromagnets. The equation he produced an equation for this was:

M = E2W 2

Where M represents the magnetic alteration, E represents the electric current, and W represents the length of the wire.

In 1840, Joule established Joule's Law which states that the heat produced in a wire by an electrical current is proportional to the resistance of the wire multiplied by the square of the current. This law is expressed by the equation:

P = I 2R

Where P represents the heat produced in a wire by an electrical current, I represents the current and R represents the resistance of the wire.

In 1841, he shifted his study from electromagnets to heat, and in 1842 he created a new theory of heat. The old theory was that heat was thought to be a substance, but his theory was that heat was actually a state of vibration. Through his experiments, he also noticed that heat could not be destroyed nor created, only changed.

He conducted many experiments...