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Power
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Power
Power
Power
Power
Power
Power
Power
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Power
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  • 1. 28 April 2010 SLO9: Calculate Power Usage All electrical appliances transfer energy. The power of an appliance is the amount of energy that it transfers every second. Power = Current x Voltage (Watts, W) (Amps, A) (Volts, V) Or P = I  V P = I V Mr Maude’s Grandma: (the very powerful) Ivy Watts James Watt (1736-1819)
  • 2. Power Watt is the power of the light bulb? I =2A, V=12V P = I  V =2  12 =24W Watt is the power of the hair drier? I =3.5A, V=240V P = I  V =3.5  240 =840W
  • 3. P I V =  P I V
  • 4. P I V = P I V
  • 5. P I V = P I V
  • 6. One piece of information is missing from these stickers, use the power formula to calculate the missing value
  • 7. 2 1 3 4 5 6 7 8 9 10 11 12
  • 8. Extra activity: School Cert. P 197, Q3, 4, 6, 7
    • Mitsubishi TV 230 88
    • Breadmaker 240 650
    • Sony PC Adapter 16 4
    • Data Projector 240 1
    • Kettle 220 2200
    • Telephone 9 0.080
    • Alarm Clock 240 6
    • Toshiba PC 15 4
    • Palm adapter 5 1
    • Toaster 240 800
    • TDK speakers 240 25
    • Goldair Heater 240 2400
    0.38 2.71 64 240 10 0.72 0.025 60 5 3.33 0.10 10 Appliance Voltage / V Current / A Power / W
  • 9. Extra activity: School Cert. P 197, Q3, 4, 6, 7
    • Mitsubishi TV 230 88
    • Breadmaker 240 650
    • Sony PC Adapter 16 4
    • Data Projector 240 1
    • Kettle 220 2200
    • Telephone 9 0.080
    • Alarm Clock 240 6
    • Toshiba PC 15 4
    • Palm adapter 5 1
    • Toaster 240 800
    • TDK speakers 240 25
    • Goldair Heater 240 2400
    0.38 2.71 64 240 10 0.72 0.025 60 5 3.33 0.10 10 Appliance Voltage / V Current / A Power / W
  • 10. Power and Energy Electricity companies charge customers for the electrical energy they use. The amount you pay will depend on 3 things:
    • What appliances you use
    • How long you use them for
    • How much a Unit of electricity costs
    The power of the appliance changes how much energy is transferred each second. The more seconds you use an appliance, the more energy is transferred. Electricity companies charge per kilowatt-hour, the amount of energy that a 1 kW appliances transfers in 1 hour.
  • 11. Power and Energy Energy is the product of power and time: Energy = Power  Time (Joules, J) (Watts, W) (Seconds, s) Or E = P  t E P t
  • 12. If the light bulb is left on for 20 seconds how much energy does it transfer? E =P  t =24  20 =480J If the hair drier is left on for 5 minutes how much energy does it transfer? E =P  t =840  (5  60) =252000J =252kJ (1kJ = 1000J) 24W 840W
  • 13. Calculate the Energy transferred by these appliances. Remember to convert time into seconds and power in Watts 40W 2 hours 2.4 kW 4.5 hours 960W 4 minutes 840W 6 minutes 60W 35 seconds Appliance Energy transferred / J Toaster Lamp Heater Light bulb Hairdrier

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