To figure out how efficient something is with energy, you can use an easy formula:

1. Efficiency (%) = (Useful Output Energy / Total Input Energy) × 100

It’s really simple!

Just take the energy you actually use (like the energy that runs your device) and divide it by the total energy you put in.

2. Example: Let’s say you get 80 joules of useful energy from 100 joules you used. Your efficiency would be:

$$\text{Efficiency} = \left( \frac{80\, \text{J}}{100\, \text{J}} \right) \times 100 = 80\%$$

This formula helps you see how well something is using energy!