Joule – one of units of measure entering the International System of Units. Not one physical quantity, and whole three – energy, work and amount of heat is measured in joules.
Introduction of the new unit of measure which received the name joule took place in 1889 on the Second international congress of electricians. That year the famous English scientist-physicist James Prescott Dzhoul died. Works of this researcher had a great influence on formation of thermodynamics. He opened communication between density of electric current at a size of electric field and the marked-out amount of heat (Joule-Lenz law), made the significant contribution to formation of the concept of the law of energy conservation. In honor of this scientist the new unit of measure also received the name joule.
The physical quantities measured in joules
Energy represents the physical quantity which expresses a measure of transition of some forms of matter in others. In the closed physical system the energy remains during the whole that time that the system remains closed – it is called the law of energy conservation.
There are different types of energy. Kinetic energy depends on speeds of the movement of points of a mechanical system, potential characterizes a stock of energy of a body which goes for acquisition kinetic, internal represents internal energy of molecular communications. There is an energy of electric field, gravitational, nuclear energy. Transformation of some types of energy into others is characterized by other physical quantity – mechanical work. It depends on size and the direction of force operating on a body and on movement of a body in space. One more important concept of classical thermodynamics – warmth. According to the first beginning of thermodynamics, the amount of heat received by a system goes for commission of the work counteracting external forces and for change of its internal energy. All three sizes are connected with each other. That there was a heat exchange as a result of which internal energy of any given system will be changed, mechanical work has to be made.
Characteristic of joule
The joule as unit of measure of mechanical work is equal to the work performed when moving a body of distance with a force of 1 meter which size is equal to 1 newton, in that direction in which this force works. In relation to calculations of energy of electric current the joule is defined as work which within one second is made by current with a force of 1 ampere at the difference of potentials equal to one volt.