Energy and Efficiency

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  • Energy and Efficiency
    • Energy can be transferred BUT cannot be CREATED or DESTROYED
      • When energy is transferred not all of it is useful, some many be given off as wasted energy.
        • Wasted energy transfers to the surrounding
    • Sankey diagrams
      • Width of arrow= amount of energy
      • Arrow continuing straight= useful energy
      • Arrows pointing down= wasted energy
    • Pay back time
      • eg. The double-glazing for a house costs £3,000 but saves £150 per year in fuel costs. What is its payback time?
        • Answer; payback time = 3,000 ÷ 150 = 20 years
      • Is something cost effective to install? How long will it take for me to start benefiting economically from it?
    • Efficiency
      • Efficiency= useful energy out / total energy in x100%
      • Efficiency= useful power out / total power in x100%
      • Formulas given in exam
    • Transfering electrical energy
      • Everyday applianes
        • Lamp; electrical energy-> heat and light energy
        • Kettle; electrical energy-> heat and sound energy
        • TV; electrical energy-> light, sound and heat energy
        • The amount of energy an appliance transfers depends on how long the appliance is switched on and its power.
      • E= P x t
        • E is energy transferred in kilowatt-hours, kWh.   P is power in kilowatts kW.    t is time in hours, h
        • E is energy transferred in joules, J.         P is power in watts, W .          t is time in seconds, s
      • How much does it cost to use a washing machine for 1.5 hours?  Power rating of washing machine = 2.0 kW cost of electricity = 6 pence per unit
        • E=P x t so, E=2x1.5. E=3
          • Units x cost per unit= total cost. So, 3 x 6p =18p

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