# Efficiency

## What Is Efficiency

**Efficiency** is *a measure of how well an object outputs useful energy, compared to how much energy is taken in*. The measure is between 0 and 1, where 1 is totally efficient. This can also be measured between 0% and 100% and is done by multiplying your answer by 100.

## Efficiency Calculations

Sometimes you will be asked to leave your answer as a **decimal** (first equation) and sometimes as a **percentage** (second question). It is important to read the question carefully to see which one it wants. If it is unspecified then you can leave your answer in either form.

## Improving Efficiency

Sometimes you will be asked **how to improve efficiency**. Like we saw last lesson, we must increase the amount of useful energy and by so doing decrease the amount of wasted energy. We can do this a number of ways such as reducing friction or by increasing the amount of insulation around an object or material.

- What is the efficiency of bulb A which has 500J input and 75J of useful output?
- Your answer should include: 0.15 / 15% / 15
- What is the efficiency of a different bulb, bulb B, with 100J input and 25J of energy is wasted?
- Your answer should include: 0.75 / 75% / 75
- Which bulb is best and why?
- Your answer should include: B / Efficient