Dictionary > Joule


The ‘joule is a derived SI unit of energy that was derived from the name of the English physicist, James Prescott Joule (the first to discover the first law of thermodynamics and proposed the mechanical theory of heat). It is a unit of electrical energy equal to the work done when a current of one ampere passes through a resistance of one ohm for one second. It may also be defined as the energy dissipated as heat as one ampere electric current passes through a resistance of one ohm for one second. A joule may also be the work required to produce 1 watt of power occurring for 1 second (Wattâ‹…second). One joule is roughly 0.001 btu. One calorie is about 4 joules. Symbol: J.


  1. McGraw-Hill Dictionary of Physics, Fifth Edition (1997). McGraw-Hill, Inc., p. 224.

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