The watt (symbol: W) is the SI derived unit of power, equal to one joule of energy per second. A human climbing a flight of stairs is doing work at the rate of about 200 watts. An automobile engine produces mechanical energy at a rate of 25,000 watts (approximately 30 horsepower) while cruising. A typical household incandescent light bulb uses electrical energy at a rate of 40 to 100 watts, while the energy-saving compact fluorescent lights which are replacing them use 8 to 20 watts Watt may refer to: Watt, a scientific unit of power, named for James Watt Watt-hour Watt balance Nominal watt Wat, a type of stew in Ethiopian cuisine; also transliterated as wet Wat, a temple For a list of people named Watt, see Watt (surname). ... Look up si, Si, SI in Wiktionary, the free dictionary. ... SI derived units are part of the SI system of measurement units and are derived from the seven SI base units. ... In physics, power (symbol: P) is the rate at which work is performed or energy is transmitted, or the amount of energy required or expended for a given unit of time. ... The joule (IPA: or ) (symbol: J) is the SI unit of energy. ... This article is about modern humans. ... “Car” and “Cars” redirect here. ... This article is about a unit of measurement. ... Light bulb redirects here. ... A spiral type compact fluorescent lamp. ...

Definition

In electrical terms, it follows that:

That is, if 1 volt of potential difference is applied to a resistive load, and a current of 1 ampere flows, then 1 watt of power is dissipated.^[1] Josephson junction array chip developed by NIST as a standard volt. ... For other uses, see Ampere (disambiguation). ...

Origin and adoption as an SI unit

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 General Conference on Weights and Measures in 1960 as the unit of power incorporated in the International System of Units (or "SI"). For other persons named James Watt, see James Watt (disambiguation). ... // The term steam engine may also refer to an entire railroad steam locomotive. ... The General Conference on Weights and Measures is the English name of the Conférence générale des poids et mesures (CGPM, never GCWM). ... “SI” redirects here. ...

Look up si, Si, SI in Wiktionary, the free dictionary. ... For other persons named James Watt, see James Watt (disambiguation). ... Majuscules or capital letters (in the Roman alphabet: A, B, C, ...) are one type of case in a writing system. ... Minuscule, or lower case, is the smaller form (case) of letters (in the Roman alphabet: a, b, c, ...). Originally alphabets were written entirely in majuscule (capital) letters which were spaced between well-defined upper and lower bounds. ... Celsius is, or relates to, the Celsius temperature scale (previously known as the centigrade scale). ...

SI multiples

Derived and qualified units for power distribution

Kilowatt

The kilowatt (symbol: kW), equal to one thousand watts, is typically used to state the power output of engines and the power consumption of tools and machines. A kilowatt is roughly equivalent to 1.34 horsepower.A one bar electric fire might use 1 kilowatt. Look up one thousand in Wiktionary, the free dictionary. ... For other uses, see Engine (disambiguation). ... This article is about a unit of measurement. ...

Megawatt

The megawatt (symbol: MW) is equal to one million (10⁶) watts. Look up million in Wiktionary, the free dictionary. ...

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. Not to be confused with lighting. ... Four aircraft carriers, (bottom-to-top) Principe de Asturias, amphibious assault carrier USS Wasp, USS Forrestal and light V/STOL carrier HMS Invincible, showing size differences of late 20th century carriers An aircraft carrier is a warship designed to deploy and in most cases recover aircraft, acting as a sea... For other uses, see Submarine (disambiguation). ... For the particle accelerator, see Superconducting Supercollider. ... For other uses, see Laser (disambiguation). ...

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. This article is about machines that produce electricity. ... A public utility is a company that maintains the infrastructure for a public service. ... A number of vehicles use a diesel-electric powerplant for providing locomotion. ... Great Western Railway No. ... A nuclear power station. ...

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). The Oxford English Dictionary print set The Oxford English Dictionary (OED) is a dictionary published by the Oxford University Press (OUP), and is the most successful dictionary of the English language, (not to be confused with the one-volume Oxford Dictionary of English, formerly New Oxford Dictionary of English, of... 1888 advertisement for Websters Dictionary Websters Dictionary is a common title given to English language dictionaries in the United States, deriving its name from American lexicographer Noah Webster. ... is the 332nd day of the year (333rd in leap years) in the Gregorian calendar. ... 1847 was a common year starting on Friday (see link for calendar). ... Science is the journal of the American Association for the Advancement of Science (AAAS). ...

Watts electrical and thermal

Watt electrical (abbreviation: We) is a term that refers to power produced as electricity, while watt thermal (abbreviation: Wt or Wth) refers to thermal power produced. These terms and abbreviations are not SI units, but they are used with the same prefixes as SI, for example megawatt electrical (MWe), gigawatt electrical (GWe), megawatt thermal (MWt) and gigawatt thermal (GWt). These terms are used by engineers 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. The difference is heat lost to the surroundings. An SI prefix (also known as a metric prefix) is a name or associated symbol that precedes a unit of measure (or its symbol) to form a decimal multiple or submultiple. ... For other uses, see Power station (disambiguation). ... Embalse (in full, Central Nuclear Embalse) is one of the two operational nuclear power plants in Argentina. ... Nuclear power station at Leibstadt, Switzerland. ...

Confusion of watts and watt-hours

Power and energy are frequently confused in the general media, for instance when a device is said to be rated at "100 watts per hour", which does not make any sense since a watt is a rate of doing work or using energy of 1 joule of energy per second. As a rate itself, a watt does not need to be followed by a time designation, unless one is talking about a change in power over time, analogous to an acceleration or deceleration.

Because a joule as a quantity of energy does not have a readily imagined size to the layperson, the non-SI unit watt-hour, often in its multiples such the kilowatt-hour or higher prefixes, is frequently used as a unit of energy, especially by energy-supply companies (electricity and natural gas suppliers) which often quote charges by the kilowatt-hour. A kilowatt-hour is the amount of energy equivalent to a power of 1 kilowatt running for 1 hour: The watt-hour (symbol W·h) is a unit of energy. ...

(1 kW·h)(1000 W/kW)(3600 s/h) = 3,600,000 W·s = 3,600,000 J = 3.6 MJ.

A megajoule (abbreviation: MJ) is a unit of energy equal to 1000000 joules. ...

See also

energy Portal

• Volt-ampere
• Conversion of units
• James Watt
• Declared net capacity (power plants)
• Orders of magnitude (power)
• Power factor
• Root mean square (RMS)
• Watt balance
• Watt-hour

Image File history File links Portal. ... In the United States the term (Volt-amps) in Electrical terms, means watts. ... Conversion of units refers to conversion factors between different units of measurement for the same quantity. ... For other persons named James Watt, see James Watt (disambiguation). ... Declared net capacity (DNC) is a measure of the contribution that a power station makes to the overall capacity of a distribution grid. ... This page lists examples of the power in watts produced by various different sources of energy. ... The power factor of an AC electric power system is defined as the ratio of the real power to the apparent power, and is a number between 0 and 1. ... In mathematics, the root mean square or rms is a statistical measure of the magnitude of a varying quantity. ... The watt balance is an electromechanical apparatus used for the precise measurement of the SI unit of electric current, the ampere. ... The watt-hour (symbol W·h) is a unit of energy. ...

References

Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 107th day of the year (108th in leap years) in the Gregorian calendar. ...

External links

• Nelson, Robert A., "The International System of Units Its History and Use in Science and Industry". Via Satellite, February 2000.