Watt
From Freepedia
The watt (symbol: W) is the SI derived unit of power.
Contents |
Definition
One watt is one joule of energy per second.
SI multiples
| Multiple | Name | Symbol | Multiple | Name | Symbol | |
|---|---|---|---|---|---|---|
| 100 | watt | W | ||||
| 101 | decawatt | daW | 10–1 | deciwatt | dW | |
| 102 | hectowatt | hW | 10–2 | centiwatt | cW | |
| 103 | kilowatt | kW | 10–3 | milliwatt | mW | |
| 106 | megawatt | MW | 10–6 | microwatt | µW | |
| 109 | gigawatt | GW | 10–9 | nanowatt | nW | |
| 1012 | terawatt | TW | 10–12 | picowatt | pW | |
| 1015 | petawatt | PW | 10–15 | femtowatt | fW | |
| 1018 | exawatt | EW | 10–18 | attowatt | aW | |
| 1021 | zettawatt | ZW | 10–21 | zeptowatt | zW | |
| 1024 | yottawatt | YW | 10–24 | yoctowatt | yW |
Origin
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.
Conversions
- One watt = 3.41214163 BTU/h
- One horsepower = 745.700 W
- One horsepower (electric) = 746 W
Derived and qualified units for power distribution
A watt is a unit of power or the amount of energy per unit time.
Kilowatt-hour, MWd
When paired with a unit of time the term watt is used for expressing energy consumption. For example, a kilowatt hour, is the amount of energy expended by a one kilowatt device over the course of one hour; it equals 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 of transmitter power in radio, see effective radiated power and nominal power.
MWe, MWt
Watt electrical (abbreviation: We) is a term that refers to power produced as electricity. SI prefixes can be used, for example megawatt electrical (MWe) and gigawatt electrical (GWe).
Watt thermal (abbreviation: Wt). This is a term that refers to thermal power produced. SI prefixes can be used, for example megawatt thermal (MWt) and gigawatt thermal (GWt).
For example, a nuclear power plant might use a fission reactor to generate heat (thermal output) which creates steam to drive a turbine to generate electricity. See nuclear proliferation for discussion of a reactor that generates 200 MWt (50 MWe), and another reactor that generates 800 MWt (200 MWe).
SI electricity units
| SI electromagnetic units | |||
|---|---|---|---|
| Quantity | Name | Symbol | Dimensions |
| Current | ampere (SI base unit) | A | A |
| Electric charge, Quantity of electricity | coulomb | C | A·s |
| Potential difference | volt | V | J/C = kg·m2·s−3·A−1 |
| Resistance, Impedance, Reactance | ohm | Ω | V/A = kg·m2·s−3·A−2 |
| Resistivity | ohm metre | Ω·m | kg·m3·s−3·A−2 |
| Electrical power | watt | W | V·A = kg·m2·s−3 |
| Capacitance | farad | F | C/V = kg−1·m−2·A2·s4 |
| Elastance | reciprocal farad | F−1 | kg·m2·A−2·s−4 |
| Permittivity | farad per metre | F/m | kg−1·m−3·A2·s4 |
| Conductance, Admittance, Susceptance | siemens | S | Ω−1 = kg−1·m−2·s3·A2 |
| Conductivity | siemens per metre | S/m | kg−1·m−3·s3·A2 |
| Magnetic flux | weber | Wb | V·s = kg·m2·s−2·A−1 |
| Magnetic flux density | tesla | T | Wb/m2 = kg·s−2·A−1 |
| Magnetic induction | ampere per metre | A/m | A·m−1 |
| Reluctance | ampere-turns per weber | A/Wb | kg−1·m−2·s2·A2 |
| Inductance | henry | H | Wb/A = V·s/A = kg·m2·s−2·A−2 |
| Permeability | henry per metre | H/m | kg·m·s−2·A−2 |
| Magnetic susceptibility | (dimensionless) | χ | - |
See also
External links
- Nelson, Robert A., "The International System of Units Its History and Use in Science and Industry". Via Satellite, February 2000.
