Contents 1 Examples 2 Origin and adoption as an SI unit 3 Multiples 3.1 Femtowatt 3.2 Picowatt 3.3 Nanowatt 3.4 Microwatt 3.5 Milliwatt 3.6 Kilowatt 3.7 Megawatt 3.8 Gigawatt 3.9 Terawatt 3.10 Petawatt 4 Conventions in the electric power industry 5 Radio transmission 6 Distinction between watts and watt-hours 7 See also 8 Notes 9 References 10 External links

Examples When an object's velocity is held constant at one meter per second against a constant opposing force of one newton, the rate at which work is done is 1 watt. 1   W = 1   J s = 1   N ⋅ m s = 1   k g ⋅ m 2 s 3 {\displaystyle \mathrm {1~W=1~{\frac {J}{s}}=1~{\frac {N\cdot m}{s}}=1~{\frac {kg\cdot m^{2}}{s^{3}}}} } In terms of electromagnetism, one watt is the rate at which electrical work is performed when a current of one ampere (A) flows across an electrical potential difference of one volt (V). 1   W = 1   V ⋅ 1   A {\displaystyle \mathrm {1~W=1~V\cdot 1~A} } Two additional unit conversions for watt can be found using the above equation and Ohm's Law. 1   W = 1   V 2 Ω = 1   A 2 ⋅ Ω {\displaystyle \mathrm {1~W=1~{\frac {V^{2}}{\Omega }}=1~A^{2}\cdot \Omega } } Where ohm ( Ω {\displaystyle \Omega } ) is the SI derived unit of electrical resistance. A person having a mass of 100 kilograms who climbs a 3-meter-high ladder in 5 seconds is doing work at a rate of about 600 watts. Mass times acceleration due to gravity times height divided by the time it takes to lift the object to the given height gives the rate of doing work or power.[i] A laborer over the course of an 8-hour day can sustain an average output of about 75 watts; higher power levels can be achieved for short intervals and by athletes.[2]

Origin and adoption as an SI unit The watt is named after the Scottish inventor James Watt for his contributions to the development of the steam engine. The measurement unit was recognized by the Second Congress of the British Association for the Advancement of Science in 1882, concurrent with the start of commercial power production from both water and steam. In 1960 the 11th General Conference on Weights and Measures adopted it for the measurement of power into the International System of Units (SI).

Conventions in the electric power industry In the electric power industry, megawatt electrical (MWe[17] or MWe[18]) refers by convention to the electric power produced by a generator, while megawatt thermal or thermal megawatt[19] (MWt, MWt, or MWth, MWth) refers to thermal power produced by the plant. For example, the Embalse nuclear power plant in Argentina uses a fission reactor to generate 2109 MWt (i.e. heat), which creates steam to drive a turbine, which generates 648 MWe (i.e. electricity). Other SI prefixes are sometimes used, for example gigawatt electrical (GWe). The International Bureau of Weights and Measures, which maintains the SI-standard, states that further information about a quantity should not be attached to the unit symbol but instead to the quantity symbol (i.e., Pthermal = 270 W rather than P = 270 Wth) and so these units are non-SI.[20] In compliance with SI the energy company DONG Energy uses the unit megawatt for produced electrical power and the equivalent unit megajoule/s for delivered heating power in a combined heat and power station such as Avedøre Power Station.[21] When describing alternating current (AC) electricity, another distinction is made between the watt and the volt-ampere. While these units are equivalent for simple resistive circuits, they differ when loads exhibit electrical reactance.

Radio transmission Main article: Effective radiated power Radio stations usually report the power of their transmitters in units of watts, referring to the effective radiated power. It refers to the relative power of the transmission when it is directed towards the horizon for maximum geographic coverage, rather than uniformly broadcast in all directions.

Distinction between watts and watt-hours The terms power and energy are frequently confused. Power is the rate at which energy is generated or consumed and hence is measured in units (e.g. watts) that represent energy per unit time. For example, when a light bulb with a power rating of 100W is turned on for one hour, the energy used is 100 watt hours (W·h), 0.1 kilowatt hour, or 360 kJ. This same amount of energy would light a 40-watt bulb for 2.5 hours, or a 50-watt bulb for 2 hours. Power stations are rated using units of power, typically megawatts or gigawatts (for example, the Three Gorges Dam is rated at approximately 22 gigawatts). This reflects the maximum power output it can achieve at any point in time. A power station's annual energy output, however, would be recorded using units of energy (not power), typically gigawatt hours. Major energy production or consumption is often expressed as terawatt hours for a given period; often a calendar year or financial year. One terawatt hour of energy is equal to a sustained power delivery of one terawatt for one hour, or approximately 114 megawatts for a period of one year. The watt second is a unit of energy, equal to the joule. One kilowatt hour is 3,600,000 watt seconds. The watt second is used, for example, to rate the energy storage of flash lamps used in photography, although the term joule is generally employed.[citation needed] While a watt per hour exists in principle (as a unit of rate of change of power with time[iii]), it is not correct to refer to a watt (or watt hour) as a "watt per hour".[22]

Notes ^ The energy in climbing the stairs is given by mgh. Setting m = 100 kg, g = 9.8 m/s2 and h = 3 m gives 2940 J. Dividing this by the time taken (5 s) gives a power of 588 W. ^ Average household electric power consumption is 1.19 kW in the US, 0.53 kW in the UK. In India it is 0.13 kW (urban) and 0.03 kW (rural) – computed from GJ figures quoted by Nakagami, Murakoshi and Iwafune.[6] ^ Watts per hour would properly refer to a rate of change of power being used (or generated). Watts per hour might be useful to characterize the ramp-up behavior of power plants, or slow-reacting plant where their power could only change slowly. For example, a power plant that changes its power output from 1 MW to 2 MW in 15 minutes would have a ramp-up rate of 4 MW/h.

References ^ International Bureau of Weights and Measures (2006), The International System of Units (SI) (PDF) (8th ed.), pp. 118, 144, ISBN 92-822-2213-6, archived (PDF) from the original on 2017-08-14  ^ Avallone, Eugene A; et. al, eds. (2007), Marks' Standard Handbook for Mechanical Engineers (11th ed.), New York: Mc-Graw Hill, pp. 9–4, ISBN 0-07-142867-4 . ^ Morfey, C.L. (2001). Dictionary of Acoustics. ^ "Bye-Bye Batteries: Radio Waves as a Low-Power Source", The New York Times, Jul 18, 2010, archived from the original on 2017-03-21 . ^ Stetzler, Trudy; Magotra, Neeraj; Gelabert, Pedro; Kasthuri, Preethi; Bangalore, Sridevi. "Low-Power Real-Time Programmable DSP Development Platform for Digital Hearing Aids". Datasheet Archive. Archived from the original on 3 March 2011. Retrieved 8 February 2010.  ^ Nakagami, Hidetoshi; Murakoshi, Chiharu; Iwafune, Yumiko (2008). International Comparison of Household Energy Consumption and Its Indicator (PDF). ACEEE Summer Study on Energy Efficiency in Buildings. Pacific Grove, California: American Council for an Energy-Efficient Economy. Figure 3. Energy Consumption per Household by Fuel Type. 8:214–8:224. Archived (PDF) from the original on 9 January 2015. Retrieved 14 February 2013.  ^ Elena Papadopoulou, Photovoltaic Industrial Systems: An Environmental Approach Springer 2011 ISBN 3642163017, p.153 ^ "2007–2008 Information Digest, Appendix A" (PDF). Nuclear Regulatory Commission. 2007. Archived (PDF) from the original on 16 February 2008. Retrieved 27 January 2008.  ^ Bai, Jim; Chen, Aizhu (11 November 2010). Lewis, Chris, ed. "China's Shanxi to face 5–6 GW power shortage by yr-end – paper". Peking: Reuters.  ^ "Not on my beach, please". The Economist. 19 August 2010. Archived from the original on 24 August 2010.  ^ "Chiffres clés" [Key numbers]. Electrabel. Who are we: Nuclear (in French). 2011. Archived from the original on 2011-07-10.  ^ Davidson, CC; Preedy, RM; Cao, J; Zhou, C; Fu, J (October 2010), "Ultra-High-Power Thyristor Valves for HVDC in Developing Countries", 9th International Conference on AC/DC Power Transmission, London: IET . ^ "Crossing the Petawatt threshold". Livermore, CA: Lawrence Livermore National Laboratory. Archived from the original on 15 September 2012. Retrieved 19 June 2012.  ^ World’s most powerful laser: 2 000 trillion watts. What’s it?, IFL Science, archived from the original on 2015-08-22 . ^ Eureka alert (publicity release), Aug 2015, archived from the original on 2015-08-08 . ^ "Construction of a Composite Total Solar Irradiance (TSI) Time Series from 1978 to present". CH: PMODWRC. Archived from the original on 2011-08-22. Retrieved 2005-10-05.  ^ Rowlett, Russ. "How Many? A Dictionary of Units of Measurement. M". University of North Carolina at Chapel Hill. Archived from the original on 2011-08-22. Retrieved 2017-03-04.  ^ Cleveland, CJ (2007). "Watt". Encyclopedia of Earth.  ^ "Solar Energy Grew at a Record Pace in 2008 (excerpt from EERE Network News". US: Department of Energy). 25 March 2009. Archived from the original on 18 October 2011.  ^ International Bureau of Weights and Measures (2006), The International System of Units (SI) (PDF) (8th ed.), p. 132, ISBN 92-822-2213-6, archived (PDF) from the original on 2017-08-14  ^ "Avedøre Power Station (Avedøre værket)". DONG Energy. Archived from the original on 2014-03-17. Retrieved 2014-03-17.  ^ "Inverter Selection". Northern Arizona Wind and Sun. Archived from the original on 1 May 2009. Retrieved 27 March 2009.

External links Look up watt in Wiktionary, the free dictionary. Borvon, Gérard, History of the electrical units, FR: Free . Nelson, Robert A (February 2000), The International System of Units: Its History and Use in Science and Industry, Via Satellite, ATI courses . v t e SI units Authority: International System of Units (BIPM) Base units ampere candela kelvin kilogram metre mole second Derived units with special names becquerel coulomb degree Celsius farad gray henry hertz joule katal lumen lux newton ohm pascal radian siemens sievert steradian tesla volt watt weber Other accepted units astronomical unit bar dalton day decibel degree of arc electronvolt hectare hour litre minute minute of arc neper second of arc tonne atomic units natural units See also Conversion of units Metric prefixes Proposed redefinitions Systems of measurement Book Category Energy portal Retrieved from "https://en.wikipedia.org/w/index.php?title=Watt&oldid=826022093#Kilowatt" Categories: SI derived unitsUnits of powerJames WattHidden categories: CS1 French-language sources (fr)Articles needing additional references from May 2017All articles needing additional referencesAll articles with unsourced statementsArticles with unsourced statements from June 2017