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conservation of energy


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energy is conserved
Energy is not created nor destroyed, it is just transferred from one form to another. 
Thermal energy always flows from a region of higher temperature to a region of lower temperature. 

efficiency= useful energy output/total energy input 

If you use the following equation, remember to add a percentage sign (%):
efficiency= useful energy output/total energy input  x 100 

4.5 describe a variety of everyday and scientific devices and situations, explaining the fate of the input energy in terms of the above relationship, including their representation by Sankey diagrams

Sankey diagrams shows what happens to the input energy and in what proportion it is transferred to various forms. For example: 
This is the Sankey diagram for a typical filament lamp.
total electrical energy is 100 j, 90 j is transferred as heat energy and 10 j transferred as light energy
Sankey diagram for a filament lamp

Ordinary electric lamps contain a thin metal filament that glows when electricity passes through it. However, most of 

the electrical energy is transferred as heat energy instead of light energy. 

The efficiency of the filament lamp is (10 ÷ 100) × 100 = 10%.

This means that 10% of the electrical energy supplied is transferred as light energy (90% is transferred as heat energy).

Heat insulation:

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