# Physics - P1.3 - Electrical Energy

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## P1.3.1 - Electrical Appliances

• Electrical appliances - extremely useful, transfer electrical energy to other forms of energy
• Common electrical appliances: lamps, electrical mixers, speakers, tvs
• Many electrical appliances transfer energy by heating - useful in things eg. kettles, but energy is often wasted - appliances designed to waste as little energy as possible
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## P1.3.2 - Electrical Power

• Power - rate at which appliance transfers energy
• Watt (W) - 1W = 1J of electrical energy to other forms every second
• Watt - too small - measured in kilowatts (kW) - 1kW = 1000W
• P = E/t
• P - power - W
• E - energy - J
• t - time for energy to be transferred - s
• Efficiency = useful power in/total power in(X 100)
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## P1.3.3 - Using Electrical Energy

• Companies supplying mains electricity charge for amont energy used - measured in kilowatt-hour (kW h) - J is too small
• Kilowatt-hour - amount of energy transferred by 1kW appliance when used for 1 hour
• E = P x t
E - energy transferred - kWh
P - power of appliance - kW
t - time taken for energy to be transferred - h
• Electricity meter - records no of kWh of energy used - if previous meter reading is subtracted from current reading, electrical energy used between readings can be calculated
• Total cost = no of kWh x cost/kWh
• Cost/kWh is given on electricity bill
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## P1.3.4 - Cost Effectiveness Matters

• To compare cost effectiveness, must consider:
- cost of installing appliance
- running costs
- maintenance costs
- environmental costs
- interest charged on loan to buy appliance
• To reduce energy bill - buy newer, more efficient appliances (eg. fridge), install materials designed to reduce energy waste (eg. loft insulation)
• Payback time - time taken for appliance or installation to pay for itself in terms of energy savings
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