Doodle Science will teach you high school physics in a less boring way in no time!

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Different types of energy can be transferred from one type to another. You can see how a car engine converts chemical energy stored in the fuel into kinetic energy in the engine and wheels to get you from A to B. In a lamp, the electrical input is converted into light energy. However, not all the energy put into it is converted into useful energy; some of it is converted into energy that we do not need, such as heat.

Sankey diagrams summarize all energy transfers that occur in a process. The thicker the arrow, the greater the amount of energy involved. This Sankey diagram for an electric lamp shows that most electrical energy is transferred as heat rather than light. This means it is very inefficient. We can calculate efficiency using this simple formula: useful energy, in this case 10 J divided by the total energy input, which is 100 J, which gives us an efficiency of 0.1 or 10% if you multiply it by 100.

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