Post on 12-Jan-2015
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Energy and Cost
Objectives:4.1 Determine the cost of using an
electrical appliance
4.4 Identify the units that define electric energy, using the
variables associated with electric circuits
Energy
Energy: the ability to do work all appliances need energy to work ex. a remote control needs energy
from batteries to work ex. a light bulb needs electrical
energy to shine bright
What is energy?
Power
Power: the rate at which energy is produced is the product of potential difference
(voltage) & current intensity
What is power?
Symbols and Units
Symbol =
Units =
Symbol =
Units =
E = P•t
Energy
Joules (J) Power
Watts (W)
Time
Seconds (s)
A stereo has a power rating of 200W & is used for 1800 seconds. How much energy is used?
E = P•t
E = (200)•(1800)
E = 360,000 J
360,000 Joules of energy were used to work the stereo
A video game has a power rating of 175W & is used for 3600 seconds. How much energy is used?
E = P•t
E = (175)•(3600)
E = 630,000 J
630,000 Joules of energy were used to work the video game
A hair dryer has a power rating of 425W & is used for 10 minutes. How much energy is used?
E = P•t
E = (425)•(600)
E = 255,000 J
255,000 Joules of energy were used to work the hair dryer
Time must be in seconds
10 min x 60 = 600 seconds
P = V•I
Power
Watts (W) Potential Difference
Volts (V)
Current
Amps (A)
A toaster requires 120V & 6A to work. What is its power?
P = V•I
P = (120)•(6)
P = 720 W
The toaster has 720 watts of power
An appliance requires 240V & 2A to work. What is its power?
P = V•I
P = (240)•(2)
P = 480 W
The appliance has a power of 480 watts
An appliance requires 120V & 12A to work. It is used for 900 seconds. How much energy is used?
P = V•I
P = (120)•(12)
P = 1440 W
Tricky Question
E = P•t
E =(1440)•(900)
E =1,296,000 J
An appliance uses 225V & 4A to work. It is used for 60 minutes. How much energy is used?
P = V•I
P = (225)•(4)
P = 900 W
Tricky Question
E = P•t
E =(900)•(3600)
E =3,240,000 J
60min x 60
Activties
P. 173, Q. 17-20
E = P•t
Energy
(kWh)Power
Watts (kW)
Time
Hours
(hr)
KWh Question
How much energy is used if a 1500 W speaker is used for 3 hours?
E = Pt = 1.5 kW * 3 hr = 4.5 kWh
Cost
Every time you use an appliance it costs money……how do you calculate
how much it will cost?C=RaPt!
(Usually Given) Must be in kW
Must be in hours
Remember: 1000 watts = 1 kW
A 4800 watt television is used for 5 hours. If the cost of electricity is $0.04kW•h, what would your bill read? (How much would it cost?)
cost = $0.04 × 4.8kW× 5h
Cost = rate of electricity x Power x Time
cost = $ 0.964800 w = 4.8 kW
A 1500 watt hair dryer is used for 30 minutes. Electricity costs $0.05/kW•h. How much does it cost to use this hair dryer for the period indicated?
cost = 0.05 × 1.5kW × 0.5 hCost = rate of electricity x Power x Time
30 min ÷ 60 min = 0.5 hrs
cost=$ 0.0375
1500 w = 1.5 kW
A 3.9 kilowatts curling iron is used for 10 minutes once a day. Electricity costs $0.05/kW•h. How much does it cost to use this curling iron for a week?
cost = 0.05 × 3.9 kW × 0.167 hCost = rate of electricity x Power x Time
10 min ÷ 60 min = 0.167 hrs
cost=$ 0.0325 X 7 days
cost=$ 0.23
Cost & Rating Plates
Every electrical appliance has a rating plate.
Rating plates allow us to calculate the electrical cost of an appliance.
Model: VCANN-1977
Serial No: 2005-13
240 V 60 Hz 4000 W
POWER
Look for
power
The rating plate for an electric hair dryer is given below.
Model: LHOPE-1979
1500 W 200V 40Hz
If the dryer is used for 30 minutes a day & the cost of electricity is $0.04/kW•h, how much would it cost to use every day?
Cost = cost of electricity x power x time
Cost =($0.04/kW•h) x (1.5kW) x (0.5h)
Cost =$0.03 or 3 ¢
The rating plate for a television is given below.
Model: CANNHOPE-2005
2500 W 250V 60Hz
If the TV is used for 2 hours a day & the cost of electricity is $0.05/kW•h, how much would it cost to use for a 30-day month?
Cost = cost of electricity x power x time
Cost =($0.05/kW•h) x (2.5kW) x (2h)
Cost =$0.25 x 30 days Cost =$7.50
If the appliance is used for 1 hour a day & the cost of electricity is $0.0475/kW•h, how much would it cost to use every day?
The rating plate for an electric appliance is given below.
Model: NOV-05
30Hz 200V 6A
Cost = cost of electricity x power x time
Cost =($0.0475/kW•h) x (1.2kW) x (1h)
Cost =$0.057 or $0.06
No power!! Recall P = VI
P = (200)(6) P = 1200 W
?
If the appliance is used for 3 hours a day & the cost of electricity is $0.05/kW•h, how much would it cost to use for a week?
The rating plate for an electric appliance is given below.
Model: RAF-2005
375V 0.2A
Cost = cost of electricity x power x time
Cost =($0.05/kW•h) x (0.075kW) x (3h)
Cost =$0.01125
No power!! Recall P = VI
P = (375)(0.2) P = 75 W
?
x 7 days Cost =$0.08
The rating plates of four different electric appliances are used below
GIN-4445
MAC-2453
I8JUL-6712
MANDANE-2445
860 W 120V
60 HZ
2 A 250 V
66 HZ
10 A
125 V
1400 W 15 A
140 V
Each appliance is used for 4 hours.
Which of these appliances would be the most expensive to use?
A)
D)
C)
B)Since the cost and
time are the same you must just look
for power…P = V x I
P = 10 x 125
P = 1250 W
P = V x I
P = 2 x 250
P = 500 W
By comparing Power it is clear to see that appliance “C” would be the most expensive!
Joule : a unit of energy Ex.: 25 g of candy contains 276 000 J
ampere : a quantity of charges per time Ex.: 15 ampere breaker
Watt : a unit of power Ex.: 100 W light bulb
Volt : energy per unit charge Ex.: AA battery has 1.5 volts
Recalling Units
J
A
W
V
Important Units to Remember
Joules Watts
W•s kW
kw•h
V•A•s
It is important to remember the following units for power and time.
Electricity uses the following units:1. Watt 4. Kilowatt-hour2. Volt 5. Joule3. Ampere
Which of the above are units of energy?
A) 1 and 3 B) 2 and 4
C) 1 and 5 D) 4 and 5
Energy Power
Joules Watts
W•s kW
kw•h
V•A•s
Which of the following units are not units of energy?
1. W2. V•A•s3. J4. A5. kW•h6. W•s
A) 1, 3, and 4 B) 1 and 4
C) 1, 4, and 6 D) 4 and 5
Energy Power
Joules Watts
W•s kW
kw•h
V•A•s
KEY POINTS
- FORMULASE = P x tP = V x ICost = cost of electricity x P x t
**make sure you have the correct units in these formulas**
- UNITSEnergy Power
Joules Watts
W•s kW
kw•h
V•A•s
Activities
Student Study Guide, Module II-16 & II-17
WORKSHEET # 16