Energy Efficiency

Energy can be transferred from one form of energy to another. However, it is not always transferred to the form of energy that we want. A device is said to be efficient if it can convert a large amount of input energy into useful energy.

  • An efficient device will only waste a small amount of its input energy
  • An inefficient device will waste most of its input energy

We calculate efficiency in terms of energy. So, to calculate the efficiency of a device, we use the formula below:

This means that the efficiency of a device is just the proportion of input energy that is transferred to useful energy output.

To calculate the percentage efficiency, the equation is:

Let’s look at an example:


If a microwave has an efficiency of 0.7 and has a total power input of 600 W, work out the useful power output.

We can rearrange the equation:

Efficiency = Useful energy / Total Input

To produce:

Useful energy = Efficiency × Total input

So, useful energy output = 0.7\times 600=420\:W

Increasing Efficiency

No device is 100% efficient, which would mean that the total input energy is transferred into useful energy. Also, no device has an efficiency greater than 100%. As this would mean that energy is being created, which breaks the law of energy of conservation.

However, devices can be made more efficient using lubrication.

Lubrication is a substance (often a liquid) that is used to reduce friction and wear between moving objects or surfaces. So, we can use lubrication to increase efficiency.