Efficiency tells us how much of the input energy is transferred in a useful way.
We have to pay for our electricity from our supplier, so wasted energy (not transferred usefully) is wasted money, so we are wanting to buy more energy efficient appliances that will save us money by wasting less energy.
Examples are LED bulbs and televisions, AAA+ rated washing machines, fridges and freezers.
You need to know the efficiency equations:
Efficiency = Total useful energy transfer / total input energy transfer
Efficiency = total useful output power / total input power
These both will give a decimal answer between 0 and 1.
To get a percentage efficiency we just multiply the decimal by 100.
E.g. 0.5 is an efficiency of 50%
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