James Prescott Joule


James Joule was born in 1818, in Manchester, England.  Through his extensive research he established that the different forms of energy - electrical, mechanical, and heat - can be changed from one to the other and are intrinsically the same. On this he based the Law of Conservation of Energy. Born to a wealthy brewery owner,  Joule inherited his father's business and was  independently wealthy enough to fund his experiments with his family's wealth and the money he made as a brewer. Besides his scientific contributions, Joule also invented electrical welding and the displacement pump.

As a child Joule suffered from a spinal disorder which forced him to do most of his schooling at home. It also resulted in him choosing his studies over physically demanding pastimes. Even though Joule went to work at the family brewery at the age of 15, he continued to be privately tutored. Between 1834 and 1837, Joule was taught by John Dalton, a famous English chemist.

Contributions to Physics

Joule's major contributions to physics were in proving that energy can neither be created or destroyed, finding the mechanical equivalent of heat, and discovering Joule's law. The idea of conservation of energy was proved by Joule in a series of experiments.  In his early years Joule proved that heat produced in a small electromagnet built by him was from electrical energy which was in turn generated by mechanical energy which powered the dynamo. From this experiment Joule concluded that the heat produced in the electromagnet was energy which came directly from the human effort that went into the machine.

In an effort to quantify mechanical work, Joule used a brass paddle wheel which was turned by falling weights, which possessed potential energy because of their position. As they fell, they lost their potential energy, which in turn provided kinetic energy to the wheel. As the paddle wheel turned, it stirred the water in a copper tub. By noting that there was a rise in the temperature of the water every time a weight fell, and by relating the rise to the falling weights, Joule was able to claim that the mechanical energy from the falling weights was being converted to heat energy in the water. He proved that the quantity of heat capable of increasing the temperature of a pound of water by 1 degree Fahrenheit requires the expenditure of a mechanical energy represented by the fall of 772 pounds through the space of one foot. Joule showed through his research, that work can be converted to heat with a fixed conversion ratio of one to the other and vice versa. His principle of Conservation of Energy became the first law of Thermodynamics, a field of physics that Joule is often referred to as the chief founder of.

In 1840, Joule in his paper 'On Production of Heat by Voltaic Electricity' submitted to the Royal Society in London, discovered that the amount of heat produced per second in a wire carrying an electric current equals the current (I) squared multiplied by the resistance (R) of the wire. The heat produced is the electric power lost (P). (P = I x I x R.) This relationship is known as Joule's Law. Initially the Royal Society displayed little enthusiasm for Joule's paper, and did not publish his complete findings. Joule's work on the relationship of heat, electricity, and mechanical work was mostly ignored until 1847.

In a landmark paper in 1848, Joule was the fist person to calculate the speed of a molecule of gas, about 1,500 feet a second for oxygen at average temperatures. This would lay the foundations for the Kinetic Theory of Gases in the future. However, renowned scientists like Michael Faraday and George Stokes, did recognize him, and in 1849, sponsored by Faraday, Joule read his paper entitled 'On the Mechanical Equivalent of Heat' to the Royal Society. Finally in 1850, the Royal Society published his paper and elected him a member. Later on  Joule also served as president of the British Association in 1872 and 1887. In 1852, William Thompson (later to become Lord Kelvin), having realized the importance of Joule's work, started collaborating with him. They worked together for eight years and developed the Joule-Thompson Effect, which explained the cooling effect experienced when gases expanded without any external work being done on them.

Joule recognized and espoused the need for standard units of electricity.  The British Association for the Advancement of Science, under the direction of Maxwell, undertook the task of creating standard units and in recognition of Joule's contribution in relating heat and mechanical motion, named the unit of energy in physics 'Joule'. One joule is defined as the work done when a force of one newton moves something a distance of 3.3ft. (1 meter) in the direction of the force.