Editing Electrical efficiency (section)

{{Short description|Useful power output per electrical power consumed}}
{{One source|date=July 2024}}

The '''efficiency''' of a system in [[electronics]] and [[electrical engineering]] is defined as useful power output divided by the total electrical power consumed (a [[vulgar fraction|fractional]] [[Expression (mathematics)|expression]]), typically denoted by the [[Greek alphabet|Greek]] small letter [[eta]] (η – ήτα).

: <math>

\mathrm{Efficiency}=\frac{\mathrm{Useful\ power\ output}}{\mathrm{Total\ power\ input}}
</math>
If energy output and input are expressed in the same units, efficiency is a [[dimensionless number]].<ref>{{cite web |url=http://www.iso.org/sites/JCGM/VIM/JCGM_200e_FILES/MAIN_JCGM_200e/01_e.html#L_1_8 |title='''1.8''' (1.6) '''quantity of dimension one''' dimensionless quantity |work=International vocabulary of metrology — Basic and general concepts and associated terms (VIM) |publisher=[[International Organization for Standardization|ISO]] |date=2008 |access-date=2011-03-22}}</ref> Where it is not customary or convenient to represent input and output energy in the same units, efficiency-like quantities have units associated with them.  For example, the [[heat rate (efficiency)|heat rate]] of a [[fossil fuel power station|fossil fuel power plant]] may be expressed in [[British thermal unit|BTU]] per [[kilowatt-hour]]. [[Luminous efficacy]] of a light source expresses the amount of visible light for a certain amount of power transfer and has the units of [[lumen (unit)|lumens]] per watt.