The document discusses key concepts related to electrical energy and power. It defines energy as the ability to do work and power as the rate at which energy is produced. The key units are identified as joules (J) for energy, watts (W) for power, volts (V) for potential difference, and amps (A) for current. Formulas for calculating energy (E=P×t), power (P=V×I), and cost of electricity are provided along with examples of calculations.

1. 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

2. Energy

Energy:
 the
Wh
en at is
er g
y?
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

3. Power

Wh
po at is
we
r?
Power:
 the
rate at which energy is produced
 is the product of potential difference
(voltage) & current intensity

4. Symbols and Units
Symbol =
Symbol =
Units
Units
=
=

5. E = P•t
Time
Energy
Joules (J)
Seconds (s)
Power
Watts (W)

6. 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

7. 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

8. 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)
Time must be in seconds
10 min x 60 = 600
seconds
E = 255,000 J
255,000 Joules of energy were
used to work the hair dryer

9. P = V •I
Power
Watts (W)
Current
Amps (A)
Potential
Difference
Volts (V)

10. 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

11. 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

12. Tric
ky
Que
s tio
n
An appliance requires 120V & 12A to work.
It is used for 900 seconds.
How much
energy is used?
P = V•I
E = P•t
P = (120)•(12)
E =(1440)•(900)
P = 1440 W
E =1,296,000 J

13. Tric
ky
Que
s tio
n
An appliance uses 225V & 4A to work. It is
used for 60 minutes. How much energy is
used?
60min x 60
P = V•I
E = P•t
P = (225)•(4)
E =(900)•(3600)
P = 900 W
E =3,240,000 J

14. Activties

P. 173, Q. 17-20

15. E = P•t
Energy
(kWh)
Time
Power
Hours
Watts
(kW)
(hr)

16. 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



17. 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
Remember: 1000 watts = 1 kW
Must be in
hours

18. 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 = rate of electricity x Power x Time
cost = $0.04 × 4.8kW× 5h
cost = $ 0.96
4800 w = 4.8 kW

19. A 1500 watt hair dryer is used for
30 minutes. Electricity costs
$0.05/kW•h. How much does it cost
to use this hair dryer for the period
indicated?
Cost = rate of electricity x Power x Time
cost = 0.05 × 1.5kW × 0.5 h
1500 w = 1.5 kW
30 min ÷ 60 min = 0.5 hrs
cost=$ 0.0375

20. A 3.9 kilowatts curling iron is used
for 10 minutes once a day.
Electricity costs $0.05/kW•h. How
much does it cost to use this curling
iron for a week?
Cost = rate of electricity x Power x Time
cost = 0.05 × 3.9 kW × 0.167 h
10 min ÷ 60 min = 0.167 hrs
cost=$ 0.0325
X 7 days
cost=$ 0.23

21. Cost & Rating Plates

Every electrical appliance has a
rating plate.
Model: VCANN-1977
Serial No:
Look
for
power
240 V
60 Hz
POWER
2005-13
4000 W
Rating plates allow us to calculate
the electrical cost of an appliance.

22. 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 ¢

23. 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

24. No power!!
Recall P = VI
P = (200)(6)
P = 1200 W
The rating plate for an electric appliance is given
below.
Model: NOV-05
30Hz
200V
6A
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?
?
Cost = cost of electricity x power x time
Cost =($0.0475/kW•h) x (1.2kW) x (1h)
Cost =$0.057 or $0.06

25. No power!!
Recall P = VI
P = (375)(0.2)
P = 75 W
The rating plate for an electric appliance is given
below.
Model: RAF-2005
375V
0.2A
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?
?
Cost = cost of electricity x power x time
Cost =($0.05/kW•h) x (0.075kW) x (3h)
Cost =$0.01125
x 7 days
Cost =$0.08

26. The rating plates of four different electric appliances are
used below
A)
860 W
120V
60 HZ
GIN-4445
B)
1400 W
Each appliance is used for 4 hours.
Which of these appliances would be the most
expensive to use?
15 A
140 V
MAC-2453
C)
10 A
125 V
MANDANE-2445
D)
2A
250 V
66 HZ
I8JUL-6712
P=VxI
Since the cost and
time are the same you
must just look
for power…
P = 10 x 125
P = 1250 W
P=VxI
P = 2 x 250
P = 500 W
By comparing Power it
is clear to see that
appliance “C” would
be the most
expensive!

27. Recalling Units

Joule : a unit of energy


W
Ex.: 100 W light bulb
Volt : energy per unit charge

A
Ex.: 15 ampere breaker
Watt : a unit of power


Ex.: 25 g of candy contains 276 000 J
ampere : a quantity of charges
per time


J
Ex.: AA battery has 1.5 volts
V

28. Important Units to Remember
It is important to remember the following units for power and time.
Joules
Watts
W•s
kW
kw•h
V•A•s

29. Electricity uses the following units:
1. Watt
4. Kilowatt-hour
2. Volt
5. Joule
3. Ampere
Which of the above are units of energy?
1 and 3
B) 2 and 4
C) 1 and 5
D) 4 and 5
A)
Energy
Power
Joules
Watts
W•s
kW
kw•h
V•A•s

30. Which of the following units are not units
of energy?
1. W
2. V•A•s
3. J
4. A
5. kW•h
6. W•s
Energy Power
1, 3, and 4
B) 1 and 4
C) 1, 4, and 6
D) 4 and 5
A)
Joules
Watts
W•s
kW
kw•h
V•A•s

31. KEY POINTS
-
FORMULAS
E=Pxt
P=VxI
Cost = cost of electricity x P x t
**make sure you have the correct units in these formulas**
- UNITS
Energy
Power
Joules
Watts
W•s
kW
kw•h
V•A•s

32. Activities


Student Study Guide, Module II-16
& II-17
WORKSHEET # 16