# Physics P1 Electrical Energy

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• Created by: Phoebe
• Created on: 08-06-12 16:07

## 3.1-3 Electrical Appliances

• An electrical appliance is designed for one particular purpose and should waste as little energy as possible
• The power of an appliance is the rate at which it transfers energy
• Power=Energy/Time
• Energy=Power x Time
• Time=Energy/Power
• Efficiency=Useful power out/Total power in (x100%)
• The kilowatt-hour is the energy supplied to a 1kW appliance in 1 hour
• Total cost=number of kWh x cost per kWh
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## 3.4 Cost effectiveness matters

• Cost effectiveness means getting the best value for money

To compare the cost effectiveness of different appliances we must consider a number of different costs, including:

• purchase cost
• installation cost
• running costs
• maintenance costs
• environmental costs
• possible interest charged if a loan has been taken

The payback time is the time it takes for an appliance to pay for itself in terms of energy saving e.g.

• Loft insulation costs £600. It saves £80 per year. How long is the payback time? 600/80=7.5 years
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