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 buying appliance
      - 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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