1. Power and Electricity Cost Physics

2. Electric Power The proportional rate of the amount of current being sent through a circuit to the amount of voltage being used to send the current. P = IV Where: – P is power; measured in Watts (W) – I is current; measured in Amps (A) – V is voltage; measured in volts (V)

3. Problem 1 The current through a car motor is 150 A. A 12 V battery is used. How much power does the the car motor have? I = 150 A V = 12 V P = ? P = IV P = (150 A)(12 V) P = 1,800 W

4. Problem 2 A small desktop radio has 8,000 W of power. If the voltage is 120 V, how much current does it draw? P = 8,000 W V = 120 V I = ?

5. Energy Energy lost or gained by any system is determined by taking the power by how long it runs for (time). Since power is measured in watts (or joules per second) and time in seconds, the unit of energy is the wattsecond (Ws) or joule (J).

6. Energy The watt-second is too small a quantity for most practical purposes, so the watt-hour (Wh) and kilowatt-hour (kWh) are defined as follows:

7. Cost of Electricity The killowatt-hour meter is an instrument used for measuring the energy supplied to a residential or commercial user of electricity. To solve for electricity cost: Total Cost = (# of kWh) x (cost of 1 kWh)

8. Problem 3 A 60 W kitchen light is left on for an entire 8 hour work shift. If the cost of electricity is $0.08 per kWh, what did it cost to leave on the light bulb?

9. Problem 4 A clothes dryer has a power rating of 4500 W. How long did it take to dry a load of laundry if electric power costs $0.09/ kWh and the cost of using the dryer was $0.63?