1. Electric Power A derived unit (one that is calculated from fundamental units. Fundamental units are measured directly.) Fundamental units of electricity are:

2. Electric Power A derived unit (one that is calculated from fundamental units. Fundamental units are measured directly.) Fundamental units of electricity are: volts (voltage), amps (current), and ohms (resistance).

3. Electric Power Measured in watts (W) or kilowatts (kW) One watt = 1 joule/second Power is the rate at which energy is flowing. Electric power can be transformed into many different types of energy. Examples:

4. Deriving the power formula If power is joules/second and it’s a derived unit, what is measured to get to joules/second? Can you think of a fundamental measurement whose units are “something”/second? Yes, coulombs/second which are current units called amps.

5. Deriving the power formula ?xcoulombs=joules Csecondsecond What could take the place of the ?’s so that we get joules/sec as the final unit? We need to cancel the coulombs, so coulombs need to be in the denominator of the “?“. What should the numerator be?

6. Deriving Power formula joules xcoulombs=joules coulombssecondsecond Recall: joules/coulombs = volts coulombs/second = amps So…

7. Calculating Power in a Circuit joulesxcoulombs=joules coulombsecondsecond VoltagexCurrent=Power P = V I or P = I V

8. Another unit of power Horsepower (hp) One hp = 746 watts Large motors are frequently ranked by horsepower (cars, garage door openers) Research how “horsepower” came to be We will use watts or kilowatts, not horsepower.