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The '''watt''' (symbol: W) is the [[SI]] unit of [[power (physics)|power]]. It is named in honour of the physicist [[James Watt]] (1736–1819).

== Definition ==

The watt is a method of measuring the rate of energy transfer of an appliance. A one watt lightbulb, for example, will change one joule of electrical energy into light energy (and some heat/sound) every second, thus "consuming" it. It is a measure of an appliance's power (appetite for joules).

The '''watt''' is the rate a source of [[energy]] uses or produces one [[joule]] during one [[second]], so the same quantity may be referred to as a '''joule per second''', with the symbol '''J/s'''. It can also be written as '''[[kilogram|kg]]·[[metre|m]]<sup>2</sup>·[[second|s]]<sup>−3</sup>'''. The more watts, the more energy used per second. That is why a higher-watt electrical appliance works faster than a lower-watt appliance.

It is equivalent to one [[volt]] [[ampere]] (1 V·A) or 1/746 of a [[horsepower]]. The power of a [[light bulb]] is measured in watts. [[Led|LED]]s have much smaller consumption of power. Example small led can be used by {{convert|0.015|W|abbr=off}} what can be also written 15 milliwatts.

Watt is a unit of power, joule is a unit of work and energy, and time is a unit of time. An equation for solving Power, Work and Time is '''Power = Work ÷ Time,''' '''Work = Power '''× '''Time, '''or '''Time = Work '''÷''' Power'''.
===Kilowatt===
1000 watts is called a kilowatt, written as kW. It is also known as (10<sup>3</sup>) watts. In many countries, electric bills are based on how many kilowatt-hours are being used.

===Megawatt===
1000000 watts is called a megawatt, written as MW. It is also known as (10<sup>6</sup>) watts. This is used to describe how much electricity is needed by a large town.

===Gigawatt===
1000000000 watts is called a gigawatt, written as GW. It is also known as (10<sup>9</sup>) watts. This is used to describe how much electricity is needed for a [[power grid]].

== Example ==
If 1000kJ of energy was used to power one lightbulb of 100W, how long will the lightbulb last for using that energy?

Because Time is unknown, but you know the other two, the correct equation would be "'''Time = Work '''÷''' Power",''' then 1,000,000J ÷ 100W = 10000 seconds. Then convert it into proper time and you'll get 2 hours, 46 minutes and 40 seconds.


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[[Category:Units of power]]
[[Category:SI derived units]]