Watt

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For other uses, see Watt (disambiguation).

The watt (symbol: W) is the SI derived unit of power, equal to one joule per second. A human being climbing a flight of stairs is doing work at the rate of about 200 watts; a highly-trained athlete can work at up to approximately 2000 watts for brief periods. An automobile engine produces 25 000 watts (approximately 30 horsepower) while cruising. A typical household incandescent lightbulb uses 40 to 100 watts.

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[edit] Definition

One watt is one joule (the SI unit of energy) per second.

1 \ \mathrm{W} = 1 \ \dfrac{\mathrm{J}}{\mathrm{s}} = 1 \ \dfrac{\mathrm{kg} \cdot \mathrm{m^2}}{\mathrm{s^3}} = 1 newton meter per second

[edit] Origin

The 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.

[edit] 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

[edit] Derived and qualified units for power distribution

[edit] Megawatt

The megawatt (symbol: MW) is equal to one million (106) watts.

Many things can sustain the transfer or consumption of energy on this scale; some of these events or entities include: lightning strikes, large electric motors, naval craft (such as aircraft carriers and submarines), engineering hardware, and some scientific research equipment (such as the supercollider and large lasers). A large residential or retail building may consume several megawatts in electric power and heating energy.

The productive capacity of electrical generators operated by utility companies is often measured in MW. Modern high-powered diesel-electric railroad locomotives typically have a peak power output of (3 to 5) MW, whereas a typical modern nuclear power plant produces a peak output on the order of 500 to 2000 MW.

According to the Oxford English Dictionary, the earliest citing for "megawatt" is a reference in the 1900 Webster's International Dictionary of English Language. The OED also says "megawatt" appeared in a 28 November 1847, article in Science (506:2).

[edit] Watts electrical and thermal

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). These terms are used to disambiguate the electric output of a thermal power station versus the (larger) thermal output. For example, the Embalse nuclear power plant in Argentina uses a fission reactor to generate 2109 MWt of heat, which creates steam to drive a turbine, which generates 648 MWe of electricity.

 This SI unit is named after James Watt. As for all SI units whose names are derived from the proper name of a person, the first letter of its symbol is uppercase (W). But when an SI unit is spelled out, it should always be written in lowercase (watt), unless it begins a sentence or is the name "degree Celsius".
— Based on The International System of Units, section 5.2.

[edit] See also

[edit] References

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    [edit] External links

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