power and energy. power power means work over a time period units = watts electric power is measured...
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Power and Energy
Power Power means work
over a time period Units = Watts Electric power is
measured in Watts
Power
Power = Current x Voltage
Watts = Amperes x Volts
P = I x V
1 kilowatt = 1000 watts
P = I x VV = I x R
Combined:P = I2 RP = V2 / R
AND
Problem 1Problem 1A CD player has 0.25 A A CD player has 0.25 A of current running of current running through it and runs on through it and runs on a 9 V battery. How a 9 V battery. How much power does it much power does it use?use?
P = V x IP = V x I
P = 9 V x 0.25 AP = 9 V x 0.25 A
P = 2.25 WP = 2.25 W
Problem 2
How many watts of power does a TV use if its total resistance is 50 ?
V = 120 V (house current) R = 50 P = V2/R
P = 1202/50
P = 14400/50
P = 288 W
The Cost of Electrical Energy
Power and Energy Electrical power costs $ You are charged by your
rate of power usage By Kilowatt Hours (kWh)
Kilowatt Hours Energy = Kilowatt Hour 1 Kilowatt Hour equals
consumption of 1 Kilowatt of power in 1 hour.
Kilowatt Hours
E = P x t kWh = Kilowatts x time Cost = Rate x kWh Rate varies: 2.25 ¢ to 8.9 ¢
Problem How much does it cost to
run a 200 W refrigerator in a month if it runs 4.5 hours per day?
(rate = 8.2 ¢/ kWh)
Solution
E = P x tt = 4.5 hrs X 30 days= 135 hrsP = 200 W = 0.2 kW
SolveE = 0.2 kW X 135 h
= 27 kWhCost = 8.2 ¢/kWh= 8.2 X 27 = 221.4 ¢= $2.21
Problem:
Assume the cost of electricity is 13 cents per kilowatt -hour. Calculate the energy used and its cost for the use of the following items:
a. 4 Watt night light for 8 hours
b. 1300 Watt microwave for 10 minutes
c. 60 Watt light bulb 6 hours a day for one year
d. 300 Watt refrigerator for 3 hours a day for one month
Assume the cost of electricity is 17 cents per kilowatt -hour. Calculate the power, energy used and its cost for the use of the following items connected to a 120 Volt electric outlet:
a. 0.5 Amp computer monitor for 12 hours
b. 10 Amp hair dryer for 5 minutes
c. 3 Amp electric drill for 30 seconds
d. 25 Amp electric clothes dryer connected to 240 Volts for 30 minutes