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The joule (/ dʒ uː l / JOOL, or / dʒ aʊ l / JOWL; symbol: J) is the unit of energy in the International System of Units (SI). [1] It is equal to the amount of work done when a force of one newton displaces a mass through a distance of one metre in the direction of that force.
The calorie is defined as the amount of thermal energy necessary to raise the temperature of one gram of water by 1 Celsius degree, from a temperature of 14.5 °C, at a pressure of 1 atm. For thermochemistry a calorie of 4.184 J is used, but other calories have also been defined, such as the International Steam Table calorie of 4.1868 J.
List of orders of magnitude for energy; Factor (joules) SI prefix Value Item 10 −34: 6.626 × 10 −34 J: Energy of a photon with a frequency of 1 hertz. [1]8 × 10 −34 J: Average kinetic energy of translational motion of a molecule at the lowest temperature reached (38 picokelvin [2] as of 2021)
The dimension of power is energy divided by time. In the International System of Units (SI), the unit of power is the watt (W), which is equal to one joule per second. Other common and traditional measures are horsepower (hp), comparing to the power of a horse; one mechanical horsepower equals about 745.7 watts.
They are used in various combinations to define the seven SI base units. The Boltzmann constant is defined to be exactly 1.380 649 × 10 −23 joules per kelvin. [1] Correspondingly, the SI units for temperature and energy are calibrated to one another so that k B kelvin = 1.380 649 × 10 −23 joules.
The joule per mole (symbol: J·mol −1 or J/mol) is the unit of energy per amount of substance in the International System of Units (SI), such that energy is measured in joules, and the amount of substance is measured in moles. It is also an SI derived unit of molar thermodynamic energy defined as the energy equal to one joule in one mole of ...
The SI unit of electric potential energy is joule (named after the English physicist James Prescott Joule). In the CGS system the erg is the unit of energy, being equal to 10 −7 Joules. Also electronvolts may be used, 1 eV = 1.602×10 −19 Joules.
Joule immersed a length of wire in a fixed mass of water and measured the temperature rise due to a known current flowing through the wire for a 30 minute period. By varying the current and the length of the wire he deduced that the heat produced was proportional to the square of the current multiplied by the electrical resistance of the ...