# Physics-Electrical energy

Electrical energy

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## Electrical energy

Electrical appliances

• Electrical appliances can transfer electrical energy into useful energy at the flick of a switch
• Uses of everyday electrical appliacnces include heating, lighting, making objects move and creating sound and visual images
• An electrical appliance is designed for a particular purpose and should waste as little energy as possible
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## Electrical energy

Electrical power

• Power is rate of transfer of energy
• P=E/t
• Efficiency=useful power out/total power in (x100%)
• P=power in watts, W
• E is the energy in joules, J
• t is the time taken (in seconds) for the energy to be transferred
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## Electrical energy

Using electrical energy

• The kilowatt-hour is the energy supplied to a 1kW appliance in 1 hour
• E=P x t
• Total cost= number of kWh x cost per kWh
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## Electrical energy

Cost effectiveness matters

• Cost effectiveness means getting the best value for money
• To compare the cost effectiveness of different appliances, we nees to take account of a number of different costs
• These may include:
• The cost of buying the appliance
• The cost of installing the appliance
• The running costs
• The maintenance costs
• Environmental costs
• The interest charged in a loan to buy the appliance
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