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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 <ul><li>Mitsubishi TV 230 88 </li></ul><ul><li>Breadmaker 240 650 </li></ul><ul><li>Sony PC Adapter 16 4 </li></ul><ul><li>Data Projector 240 1 </li></ul><ul><li>Kettle 220 2200 </li></ul><ul><li>Telephone 9 0.080 </li></ul><ul><li>Alarm Clock 240 6 </li></ul><ul><li>Toshiba PC 15 4 </li></ul><ul><li>Palm adapter 5 1 </li></ul><ul><li>Toaster 240 800 </li></ul><ul><li>TDK speakers 240 25 </li></ul><ul><li>Goldair Heater 240 2400 </li></ul>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 <ul><li>Mitsubishi TV 230 88 </li></ul><ul><li>Breadmaker 240 650 </li></ul><ul><li>Sony PC Adapter 16 4 </li></ul><ul><li>Data Projector 240 1 </li></ul><ul><li>Kettle 220 2200 </li></ul><ul><li>Telephone 9 0.080 </li></ul><ul><li>Alarm Clock 240 6 </li></ul><ul><li>Toshiba PC 15 4 </li></ul><ul><li>Palm adapter 5 1 </li></ul><ul><li>Toaster 240 800 </li></ul><ul><li>TDK speakers 240 25 </li></ul><ul><li>Goldair Heater 240 2400 </li></ul>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: <ul><li>What appliances you use </li></ul><ul><li>How long you use them for </li></ul><ul><li>How much a Unit of electricity costs </li></ul>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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