Ch. 2 Sec. 5 Electric Power

power• rate @ which energy is

transformed from one form to another

PV C

POWER= VOLTAGE X CURRENT

• A household light bulb has approximately 0.5 amps of current flowing through it. Since the standard household voltage is 120 volts, what is the power rating for this bulb?

• P= V X I

• P= 120 volts X 0.5 amps

(Watts= Volts X Amps)

P= 60 watts

• A hair dryer has a power rating of 1,200 watts and uses a standard voltage of 120 volts. What is the current through the hair dryer?

• P= V X I

• 1,200 watts = 120 volts X I

• 1,200/120= 10 amps

POWER= VOLTAGE X CURRENT

ENERGY= POWER X TIME

kilowatt-hours= kilowatt x hour

Ten 100-watt light bulbs are turned on for 1 hour. How much energy do they use?

(kilowatt= 1,000 watts)

Answer the following questions.

1. The voltage of a car battery is 12 volts. When the car is started, the battery produces a 40-amp current. How much power does it take to start the car?

2. An electric water heater that uses 40 kW runs for 5.0 hours. How much energy is it using?

3. What is the energy usage of the same water heater if it was run for 20 hours?