James Prescott Joule

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James Prescott Joule (24 December 1818 – 11 October 1889) was an English physicist and brewer, born in Salford, Lancashire.

James Prescott Joule

Biography

James Prescott Joule was born in Salford, Lancashire, England on 24 December, 1818. While young, Joule was mostly home-schooled but also studied Geometry and Arithmetic under John Dalton, an English chemist, physicist, and meteorologist who laid the framework for modern atomic theory. He was also later taught by the famous scientist John Davies, and was influenced greatly in his early years by chemist William Henry.

Joule's occupation as an adult was the management of the family brewery. His pursuit of scientific discoveries was merely a passionate hobby.Around the year 1840 he decided to investigate the feasibility of replacing his brewery's steam engines with one powered by the newly invented electric motor. This led him to a desire to determine the efficiency of steam compared to the efficiency of electricity. His discovered Joule's first law in 1841, which states: "the heat which is evolved by the proper action of any voltaic current is proportional to the square of the intensity of that current, multiplied by the resistance to conduction which it experiences." He realized that the steam engine of his time was more efficient and economical than the new electric motors, Joule developed a common standard to provide the output of alternative methods. The foot-pound defined as the ability to raise one pound a height of one foot.

However, having achieved his initial goal, Joule broadened his inquisitiveness and set out to determine how much work could be extracted from a given source. While working on this question he performed experiments and published results which showed that the heating effect he had quantified a few years earlier was due directly to the generation of heat within the conductor. This went squarely against the prevalent caloric theory of the time which stated that heat could not be created or destroyed, but merely transferred from one medium to another.

Motivated in part by a businessman's desire to quantify the economics of the choice, and in part by his scientific inquisitiveness, he set out to determine which prime mover was more efficient. He discovered Joule's first law in 1841, that the heat which is evolved by the proper action of any voltaic current is proportional to the square of the intensity of that current, multiplied by the resistance to conduction which it experiences.[2] He went on to realize that burning a pound of coal in a steam engine was more economical than a costly pound of zinc consumed in an electric battery. Joule captured the output of the alternative methods in terms of a common standard, the ability to raise one pound, a height of one foot, the foot-pound.

However, Joule's interest diverted from the narrow financial question to that of how much work could be extracted from a given source, leading him to speculate about the convertibility of energy. In 1843 he published results of experiments showing that the heating effect he had quantified in 1841 was due to generation of heat in the conductor and not its transfer from another part of the equipment. This was a direct challenge to the caloric theory which held that heat could neither be created or destroyed. Caloric theory had dominated thinking in the science of heat since introduced by Antoine Lavoisier in 1783. Lavoisier's prestige and the practical success of Sadi Carnot's caloric theory of the heat engine since 1824 ensured that the young Joule, working outside either academia or the engineering profession, had a difficult road ahead. Supporters of the caloric theory readily pointed to the symmetry of the Peltier-Seebeck effect to claim that heat and current were convertible in an, at least approximately, reversible process.

Major Contributions to Physics

Joule Heating

Joule Heating or Resistive Heating is a process by which the flow of a current through a conductor with some resistance releases heat. The square of the current in the conductor is proportional to the amount of heat produced according to the formula:

[math]\displaystyle{ H \propto I^2 \cdot R \cdot t }[/math]

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