Today we celebrate the birthday of James Prescott Joule (24 Dec 1818 – 11 Oct 1889), the English physicist famous for his discovery that the different forms of energy – mechanical, electrical, and heat – are essentially the same thing, and as such are interchangeable.

In wind energy farms, wind energy (a mechanical energy) is converted to electric energy. In the process, some loss occurs in the form of heat generated. Joule’s important contribution was to figure out that the total energy (mechanical + electrical + heat), however, remains constant.
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This discovery lead to his formulation of the First Law of Thermodynamics – the Law of Conservation of Energy. The law states that energy cannot be created or destroyed, but can only be changed from one form to another.

Some of his other important contributions to physics include the definition of the relationship between electrical current, resistance and heat, and also, some 10 years later, the kinetic theory of gases.

His important contributions to the understanding of energy was acknowledged when his name was given to the SI unit for energy – the joule (J).