3.  POWER: the rate of change in energy; also the rate at which work is done or energy is transformed  JOULE (J): the unit for measuring energy  WATT (W): one joule (J) of energy transformed in one second

4.  ELECTRICAL POWER: the rate of change in electrical energy  Electric loads change electrical energy into other types of energy  The amount of electrical energy changed or transformed on a load per second is the power rating of the load  Ex. a 60W light bulb uses 60J of electrical energy every second and produces 60J of heat/light energy

5. IIt is more common to calculate electrical power using voltage and current rather than energy and time. EElectrical power (P) is the product of voltage (V) and current (I)  P=VI (or P=V x I) Practice Question: If a 6.0V battery provides a current of 2.0A, what is the battery’s power output?

6.  POWER RATING: a measurement of how much electrical energy an electrical device consumes for every second it’s in use  REMEMBER: power is the rate of change of energy  1.0W is the transfer of 1.0J of energy/second Ex.: a 1500W hair dryer uses 1500J of electrical energy each second

7.  We can figure out the amount of electrical energy that a device consumes by looking at its power rating and the amount of time it’s used for. POWER is the energy transferred (E) per time interval (t)  P=E/t (or P =E divided by t)  This formula can be rearranged to find the ELECTRICAL ENERGY (E)  E (in joules) = P (watts) x t (sec.) Practice Question: How much electrical energy is consumed by a 1200W hair dryer if it is used for 5.0min.?

8.  Small items can use a lot of energy. A hair dryer being used for 5 minutes consumes 360 000 J of energy! Can you imagine how big this number would be for larger items? A larger unit of energy that you can measure in is kilowatts and the unit of time is in hours.  1 kW = 1000 W  1 h = 3600 sec.  KILOWATT-HOUR: the product of power in kilowatts and time in hours kilowatt-hour = 1.0 kilowatt x 1.0 hour  1.0kWh = 1.0 kW x 1.0 h

9.  Ex.: A family uses 1500 kW x h of electrical energy in December. If they are charged 7 cents for every kWh, how much will they be charged in total?