1. Energy and Power

2. Energy Energy: the ability to do work
What is
energy?
Energy:
the ability to do work
all appliances need energy to work
ex. a hair dryer needs to be plugged in to get energy to work
ex. a remote control needs energy from batteries to work

3. Power
What is
power?
Power:
the rate at which energy is used or the amount of work done per second
is the product of potential difference (voltage) & current intensity

4. Symbols and Units POWER ENERGY E P Watts Joules Symbol = Units =

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

6. Example #1
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. Example #2
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. Example #3
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

9. Kilowatt Hours
Energy is commonly measured in Joules (J), but can also be measured in kilowatt hours (KWh).
1 kWh = J
KWh is used by Hydro Quebec to calculate your energy bill

10. FORMULA
V = P/I
Current
Amps (A)
Voltage
Volts (V)
Power
Watts (W)

11. Example #1 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

12. Example #2 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

13. Example #3 2nd- Solve Energy 1st - Solve Power E = P•t P = V•I
An appliance requires 120V & 12A to work. It is used for 900 seconds. How much energy is used?
2nd- Solve Energy
1st - Solve Power
E = P•t
P = V•I
P = (120)•(12)
E =(1440)•(900)
P = 1440 W
E =1,296,000 J

14. Example #4 2nd- Solve Energy 1st - Solve Power E = P•t P = V•I
An appliance uses 225V & 4A to work. It is used for 60 minutes. How much energy is used?
2nd- Solve Energy
1st - Solve Power
60min x 60
E = P•t
P = V•I
P = (225)•(4)
E =(900)•(3600)
P = 900 W
E =3,240,000 J

15. Challenging question
A circuit has a resistance of 5Ω. If the battery powering the circuit has a voltage of 10V, how much power is used to run this circuit?
R=V/I
I= q/t
V=E/q
P=E/t
V=P/I
R = 5Ω V = 10 V
P= ?
I = ?
Step 1
R=V/I
5 = 10 / I
5 I = 10
I = 10/5
I = 2 A
Step 2
V=P/I
10 = P/2
10 * 2 = P
P = 20 watts