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Science

Charge, current and power

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Some electrical appliances transfer energy more efficiently than others. The power of an appliance can be calculated. The current flowing through an appliance can be calculated, allowing the most appropriate fuse to be chosen.

Choosing appliances

People have a choice when deciding which new appliance to buy. Some are more efficient at transferring energy than others. For example, less energy is 'wasted' as heat energy from energy-saving lamps (such as LEDs) and compact fluorescent lamps (CFLs) than from filament lamps.

Filament lamps

Filament 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. This is a Sankey diagramSankey diagram: A diagram using arrows to show the amounts of energy transferred in different forms. 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

Energy-saving lamps

Modern energy-saving lamps work in a different way. They transfer a greater proportion of electrical energy as light energy. This is a Sankey diagram for a typical energy-saving lamp.

total electrical energy is 100 j. 25 j is transferred as heat energy and 75 j transferred as light energy

Sankey diagram for a typical energy-saving lamp

You can see that with the energy-saving lamp, much less electrical energy is transferred - or 'wasted' - as heat energy.

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