Electric PowerA derived unit (one that is calculated from fundamental units. Fundamental units are measured directly.)

Fundamental units of electricity are:

Electric PowerA 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).

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:

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.

Deriving the power formula

? x coulombs = joules C second second

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?

Deriving Power formula

joules x coulombs = joules coulombs second second

Recall: joules/coulombs = volts

coulombs/second = amps

So…

Calculating Power in a Circuit

joules x coulombs = joules coulomb second second

Voltage x Current = Power

P = V I or P = I V

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.