Efficiency Summary

Efficiency is a measure of how well something does its job.

We calculate it using the formula: useful energy/total energy
e.g. 40/50 = 0.80

Efficiency is normally given as a percentage, so 0.80 would be 80%

Since power is just energy per second, we can also calculate it from: useful power/total power.

Using efficient electrical devices saves money and energy.
They can also help reduce climate change.

How Science Works: efficient shower and torch.