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James Prescott JOULE

Salford 24.December.1818 - Sale 11.October.1889



Little more than   twenty years,    while it completes experiments   alternating them to the conduction of the brewery of the father, it discovers the law that it determines the heat produced from the electric current who passes in an electric circuit (“law of joule”). The heat, asserts the law, it is proportional them to the resistance and the square of the current crosses that it. The law of    Joule is of fundamental importance for   to measure the heat losses that happen in every electric circuit (and in order to calculate, on the contrary, how much heat can be obtained from one stews electrical worker). Remained unassailable through the times, it will have a single exception, with the discovery of the phenomenon of the superconductivity.

Its search has been thus important that it has been given its name to an unit of measure of the job (or the energy), the joule (j).





When a current crosses a resistance R has the heating of this last one. It is the Joule effect. The energy quantum W (expressed in Joule) dissipated in heat in the time t (express in second) depends from the square of the current and is defined from the relation in figure.

The phenomenon is indispensable, as an example, in the filament of a light bulb to incandescence, in stoves the electrical workers, in irons from I iron and in the fuses you mail to protection of the wirings. It is, instead, useless and harmful when the necessity is not had to produce heat electrically.
In the members electrical workers, if the current exceeds the previewed limit, the Joule effect creates overheating and deterioration of the insulator.