Watt-hour
From Free net encyclopedia
The watt-hour (symbol W·h) is a unit of energy. The watt-hour is not an SI unit because it contains the non-SI unit hour. The SI unit of energy is the joule (J).
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Definition
One watt-hour is equivalent to one watt of power used for one hour. This is equivalent to 3,600 joules. For example, a sixty watt light bulb uses 60 watt-hours of energy every hour. Similarly, a 100 watt light bulb uses 50 watt-hours in thirty minutes.
Multiples
Milli-, kilo-, mega-, giga-, and tera- are the most-used prefixes.
| Multiple | Name | Symbol | Multiple | Name | Symbol | |
|---|---|---|---|---|---|---|
| 100 | watt hour | W·h | ||||
| 103 | kilowatt hour | kW·h | 10–3 | milliwatt hour | mW·h | |
| 106 | megawatt hour | MW·h | 10–6 | microwatt hour | µW·h | |
| 109 | gigawatt hour | GW·h | 10–9 | nanowatt hour | nW·h | |
| 1012 | terawatt hour | TW·h | 10–12 | picowatt hour | pW·h | |
| 1015 | petawatt hour | PW·h | 10–15 | femtowatt hour | fW·h | |
| 1018 | exawatt hour | EW·h | 10–18 | attowatt hour | aW·h | |
| 1021 | zettawatt hour | ZW·h | 10–21 | zeptowatt hour | zW·h | |
| 1024 | yottawatt hour | YW·h | 10–24 | yoctowatt hour | yW·h |
Conversions
| from / to | Joule | Watt-hour | Electronvolt | Calorie |
|---|---|---|---|---|
| 1 J = 1 kg m2 s-2 = | 1 | 0,278 · 10−3 | 6,241 · 1018 | 0,239 |
| 1 kW h = | 3,6 · 106 | 1000 | 22,5 · 1024 | 0,860 · 106 |
| 1 eV = | 0,1602 · 10−18 | 44,5 · 10−27 | 1 | 33,8 · 10−21 |
| 1 cal = | 4,1868 | 1,163 · 10−3 | 0,261 · 1018 | 1 |
Explanation
The watt-hour is derived from the multiplication of the SI unit of power (watt) and the non-SI unit of time (hour).
The kilowatt-hour is commonly used for electrical and natural gas energy. Many electric utility companies use the kilowatt-hour for billing. This is a convenient unit because the energy usage of a typical home in one month is several hundred kilowatt-hours. Megawatt-hours are used for metering of larger amounts of electrical energy. For example, a power plant's daily output is likely to be measured in megawatt-hours.
The Board of Trade Unit or B.O.T.U. is an obsolete UK synonym for kilowatt-hour. The term derives from the name of the government department that regulated the electricity industry. The B.O.T.U. should not be confused with the British thermal unit or BTU, which is a much smaller quantity of thermal energy.
See also
de:Wattstunde es:Kilovatio-hora fr:Kilowatt-heure ko:와트시 it:Wattora nl:Kilowattuur ja:キロワット時 no:Kilowattime nn:Kilowattime pl:Kilowatogodzina pt:Quilowatt-hora ru:Киловатт-час sl:Kilovatna ura fi:Kilowattitunti sv:Wattimme zh:千瓦·時