Watt (Energy)
Watt
| Topics: |
| SI multiples of watt | ||||||
|---|---|---|---|---|---|---|
| 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 | |
Definition
The watt (symbol: W) is the SI unit of power defined as one joule of energy transferred or dissipated in one second (J/s). Its expression in terms of [[SI] base units] is m2·kg·s-3.
The watt is a common unit of electrical power, in which case one watt of power is expended when one ampere of direct current flows through a resistance of one ohm. 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 or Wth) refers to thermal power produced; again SI prefixes can be used, for example megawatt thermal (MWt) and gigawatt thermal (GWt).
For perspective, the approximate heat dissipation from an adult human is around 100 Wt. A typical kitchen microwave will be rated around 1000 W (1 kW) and a typical automobile's power output rating will be around 150 kW.
History
The unit is named for James Watt (1736-1819), the Scottish inventor, instrument maker and mechanical engineer, renowned for his improvements on the steam engine.
Conversions
1 watt = 1 joule/second
1 watt = 1 volt ampere
1 watt = 1·107 ergs/second
1 watt = 2.39006·10-4 kilocalorie (thermal)/second
1 watt = 9.48452·10-4 Btu (thermal)/second
Further Reading
- How Many? A Dictionary of Units of Measurement, Russ Rowlett, Center for Mathematics and Science Education, University of North Carolina at Chapel Hill
- SI base units and SI derived units, the Physics Laboratory, National Institute of Standards and Technology
- Energy conversion tool at unitconversion.org.
