James Prescott Joule

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James Prescott Joule

Birth Date: December 24, 1818Birth Place: Salford, Greater Manchester, United Kingdom James Joule was interested in the efficiency of electric motorsHe was motivated by theological beliefs and as a result he began attempting to demonstrate the unity of forces in nature.


In the 1840s he determined the mechanical equivalent of heat by measuring change in temperature produced by the friction of a paddlewheel attached to a falling weight (Famous Scientists, 2013).James Joule worked with Thomson on experiments. One of these experiments involved the decrease in temperature associated with the expansion of a gas without the performance of external work. This cooling of gases as they expand is known as the “Joule—Thomson effect.” This principle provided the basis for the development of the refrigeration industry.

He had an influence the theory of conservation of energy which is the First Law of Thermodynamics.


He discovered heat dissipated by a resistor is given by the equation Q=I2 Rt. I is the current, R is the resistance, and t is the time. This equation is now known as Joule’s law (Science Museum, 2012).

James Prescott Joule



James Joule’s experiments showed that heat is produced by motion, and this contradicts with the caloric theory (Eric W. Weisstein,2007).


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