Electrical Power is rate at which energy flows Power (P) is measured in Watts (W) Power = current x voltage P = I x V Divide Multiply So, to find Current, we need to DIVIDE power by voltage. I = P V P watts I V And, to find Voltage, we need to DIVIDE power by current. V = P I amps volts

Where do Power Units come from? Power = Voltage x Current Joules Joules Coulomb second Coulomb second (Watts) (volts) (amps) = x

Electrical Power Problem If a CD player uses 4.5 V with 0.2 amps of current, what is the power it uses? P= I x V P = ? P = 0.2 A x 4.5 V I = 0.2 A P = 0.9 Watts V = 4.5 V

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Is measured in kilowatt-hours Electrical Energy = power x time Kilo means 1000x Electrical Energy = power x time E = P x t Divide Multiply So, to find power, we need to DIVIDE energy by time. P = E t E kWhr And, to find time, we need to DIVIDE energy by power. t = E P P kW t hr

Electrical Energy Problem You use your hairdryer for 10 minutes everyday. The hairdryer uses 1000 watts. How many kilowatt-hours does your hairdryer use in 12 days? E = P x t E = 1 kW x 0.17 hr E = P = 1000 W = 1 kW 0.17 x 12 days= 2 kWhr t = 10min / 60 = 0.17 hr

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