Efficiency

Efficiency Calculations

If you know the amount of input energy and useful energy from an energy transfer, you can calculate the efficiency using the following equation:

\color{aa57ff}{\text{efficiency}} \color{aa57ff}{=}\color{aa57ff}{\dfrac{\text{useful output energy}}{\text{total input energy}}}

Remember that the total energy is equal to the sum of the useful energy and the wasted energy. 

\color{aa57ff}{\text{total energy}}\color{aa57ff}{=}\color{aa57ff}{\text{useful energy} + }\color{aa57ff}{\text{wasted energy}}

You can also calculate efficiency using the total power input and the useful power input using the following equation:

\color{aa57ff}{\text{efficiency}}\color{aa57ff}{=} \color{aa57ff}{\dfrac{\text{useful power output}}{\text{total power input}}} 

Increasing Efficiency

The efficiency of an energy transfer can be increased by reducing the amount of wasted energy. How we do this depends on the system and the types of energy store involved. 

For example, by using oil as a lubricant in a car engine, less heat is produced by friction. Therefore, less energy is wasted as heat and so more energy is converted to useful energy and the engine is more efficient. 

We always want to make a process more efficient because this will save energy and money.