Watt
The watt (symbol: W) is the SI derived unit for power. It is equivalent to one joule per second (1 J/s), or in electrical units, one volt ampere (1 V·A).
It is the rate in joules per second at which energy is being converted, used, or dissipated.
- Equations: <math>\mbox{ W} = \frac{\mbox{J}} {\mbox{s}} = \frac{\mbox{N·m}} {\mbox{s}} = \frac{\mbox{kg·m}^2} {\mbox{s}^3} = \mbox{ V·A}<math>
The unit watt is named after James Watt for his contributions to the development of the steam engine, and was adopted by the Second Congress of the British Association for the Advancement of Science in 1889 and by the 11th Conférence Générale des Poids et Mesures in 1960.
A unit of power multiplied by a unit of time is a common format for expressing energy. For example, a kilowatt hour, the amount of energy expended by a one kilowatt device over the course of one hour, is 3.6 megajoules. A megawatt day (MWd or MW·d) is equal to 86.4 GJ. These units are often used in the context of power plants and home energy bills.
For the use of watts as a measurement in broadcasting, see effective radiated power and nominal power for a full discussion.
SI electricity units
| SI electromagnetism units | |||
|---|---|---|---|
| Name | Symbol | Dimensions | Quantity |
| ampere (SI base unit) | A | A | Current |
| coulomb | C | A·s | Electric charge, Quantity of electricity |
| volt | V | J/C = kg·m2·s−3·A−1 | Potential difference |
| ohm | Ω | V/A = kg·m2·s−3·A−2 | Resistance, Impedance, Reactance |
| ohm metre | Ω·m | kg·m3·s−3·A−2 | Resistivity |
| farad | F | C/V = kg−1·m−2·A2·s4 | Capacitance |
| farad per metre | F/m | kg−1·m−3·A2·s4 | Permittivity |
| reciprocal farad | F−1 | kg1·m2·A−2·s−4 | Elastance |
| siemens | S | Ω−1 = kg−1·m−2·s3·A2 | Conductance, Admittance, Susceptance |
| siemens per metre | S/m | kg−1·m−3·s3·A2 | Conductivity |
| weber | Wb | V·s = kg·m2·s−2·A−1 | Magnetic flux |
| tesla | T | Wb/m2 = kg·s−2·A−1 | Magnetic flux density |
| ampere per metre | A/m | m−1·A | magnetic induction |
| ampere-turns per weber | A/Wb | kg−1·m−2·s2·A2 | Reluctance |
| henry | H | V·s/A = kg·m2·s−2·A−2 | Inductance |
| henry per metre | H/m | kg·m·s−2·A−2 | Permeability |
| (dimensionless) | - | - | Magnetic susceptibility |
See also
External link
- Nelson, Robert A., "The International System of Units Its History and Use in Science and Industry". Via Satellite, February 2000.
Categories: SI derived units | Units of power