# Efficiency

## Efficiency is the ratio between the useful energy output and the energy input

A general definition of efficiency is the ratio between *the useful energy or power output* and *the energy or power input* - and can be expressed as

μ = E_{o}/ E_{i }(1)

where

μ = efficiency

E_{o}= useful energy or power output(Joules, W)

E_{i}= energy input or power (Joules, W)

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