User:Milton Beychok/Sandbox: Difference between revisions

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The '''kilowatt hour''' (symbol '''kWh''' or '''kW·h''') is a unit of [[Energy (science)|energy]] equal to 1000 [[Watt (unit)|watt]] hours or 3.6 [[SI#prefixes|mega]][[joule]]s. Energy in kilowatt hours is the multiplication of [[Power (physics)|power]] in [[SI#prefixes|kilo]][[watt]]s and [[time]] in hours. The kilowatt hour is most commonly known as a billing unit for electrical energy delivered to consumers by electric service providers.


==Definition==
The standard unit of energy in the [[International System of Units]] (SI) is the [[joule]] (J), equal to one [[watt]] [[second]]. Inversely, one watt is equal to 1 J/s and thus one kilowatt hour is 3.6 × 10<sup>6</sup> joules or 3.6 [[SI#prefixes|mega]][[joule]]s, which is the amount of energy expended if [[Work (Physics)|work]] is done at a constant rate of one thousand watts for one hour.
==Examples==
*A heater, rated at 1000 watts (1 kilowatt), operating for one hour uses one kilowatt hour (equivalent to 3.6  megajoules) of energy.
*Using a 60 watt [[light bulb]] for one hour consumes 0.06 kilowatt hours of energy in the form of [[electricity]]. Using a 60 watt light bulb for one thousand hours consumes 60 kilowatt hours of electricity.
*If a 100 watt light bulb is on for one hour per day for 30 days, the energy used is 100 W × 30 h = 3000 Wh = 3 kWh (equivalent to 10.8 megajoules).
==Symbol for kilowatt hour==
The International System of Units<ref name=BIPM>{{cite paper|author=Bureau International des Poids et Mesures|date=2006|url=http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf|title=The International System of Units (SI)|version= 8th edition}} See Section 5.1 Symbols.</ref> states that when compound unit symbols are formed by multiplication, the individual symbols should be separated by a half-high dot or a space (for example, "kW·h" or "kW h"). One guide published by [[NIST]]<ref>Taylor, Barry N. (1995). [http://physics.nist.gov/Document/sp811.pdf Guide for the Use of the International System of Units (SI)] Special publication 811, [[National Institute of Standards and Technology]]. See pages 12 – 13 of the guide (pages 24 – 25 of the PDF).</ref> specifically recommends avoiding "kWh" in order "to avoid possible confusion". However, "kWh" continues to be very commonly used in commercial, educational, scientific and media publications.
==References==
{{Reflist}}

Revision as of 00:15, 23 January 2010

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