How do you work out energy efficiency?

Question

How do you work out energy efficiency?

Answer 1

The Law of Conservation of Energy states that all energy that goes into a device must come out.  No energy is lost.

To calculate the efficiency of an energy transfer we use the equation:

Efficiency= useful energy output / total energy input

Example:

A light bulb is not 100% efficient.  Not all of the energy is changed into light; some of it is changed into heat.  In this case 200J of electrical energy enter the bulb, 8J is changed into light energy and 192J is changed into heat.  

Using the equation above, the efficiency of the bulb= 8/200 X 100%= 4%