The document discusses calculating power usage and energy transfer for various electrical appliances. It provides the formulas for calculating power as power equals current multiplied by voltage. It then gives examples of calculating the power of different appliances like a light bulb and hair dryer based on their current and voltage. It further explains how energy is calculated by multiplying power by time. It provides examples of calculating the energy transferred by appliances over different time periods.

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

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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