Efficiency
As mentioned in the article about conservation of energy, energy cannot be created or destroyed.
But it can be transferred from one form to another: and sometimes, we don’t want that energy form.
For example, in a computer CPU, we want the energy to be transferred as efficiently as possible so that as little heat is produced as possible.
Calculating efficiency as a decimal
Section titled “Calculating efficiency as a decimal”The formula for calculating efficiency as a decimal is:
Or, if we’re instead measuring the power used and produced, we can use:
Calculating efficiency as a percentage
Section titled “Calculating efficiency as a percentage”The formula for calculating efficiency as a percentage is:
If we’re instead measuring the power used and produced, we can use:
100% efficiency
Section titled “100% efficiency”Almost nothing can be 100% efficient, because there are always some energy losses in the system.
For example, in a car engine, some of the energy from the fuel is lost as heat and sound, so the efficience isn’t anywhere close to 100%.
However: all energy transfers usually will end up as heat in the end. In a way, heating machines (e.g. electric radiators) are 100% efficient, in that they transfer all the energy they use into heat energy - which is what we want them to do!
Examples
Section titled “Examples”A machine uses 1000 J of energy to produce 800 J of useful energy. What is the efficiency of the machine?
Section titled “A machine uses 1000 J of energy to produce 800 J of useful energy. What is the efficiency of the machine?”(or 80%)
A machine uses 2000 J of energy to produce 1500 J of useful energy. What is the efficiency of the machine?
Section titled “A machine uses 2000 J of energy to produce 1500 J of useful energy. What is the efficiency of the machine?”(or 75%)