5.10 energy and power energy (e) the ability to do work measured in joules (j) power (p) the...
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5.10 Energy and Power
Energy (E)the ability to do workMeasured in Joules (J)
Power (P)the amount of work that can be
accomplished in a certain amount of timeMeasured in Watts (W)
Energy
the ability to do workall 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
What is energy?
Power
the rate at which energy is used or the amount of work done per second
Is measured in WattsA microwave that uses more Watts
will heat food faster!
What is power?
Symbols and Units
Symbol =
Units =
Symbol =
Units =
Power
Watts (W)
Energy
Joules (J)
Time
Seconds (s)
E = P x Δt
A stereo has a power rating of 200W & is used for 1800 seconds. How much energy is used?
E = P x Δt = 200 x 1800E = 360 000J
A video game has a power rating of 175W & is used for 3600 seconds. How much energy is used?
E = 630,000 J 630,000 Joules of energy were used to work the video game
E = P x Δt
= 175 x 3600
A hair dryer has a power rating of 425W & is used for 10 minutes. How much energy is used?
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
E = P x Δt
= 425 x 600
How do we pay for the energy we use?
Energy can also be measured in kilowatt hours (kWh). If we use 1000W in 1 hour, we consume
1 kWh = 3 600 000 J
KWh is used by Hydro Quebec to calculate your energy bill
For a average summer day. Mrs “I” uses 44 kWhs. 30 kWh x $0.0532 = $1.596 14 kWh x $0.0751 = $1.051
$2.647
This is just for ONE day.
P = IV
Power
Watts (W)Current
Amps (A)
Voltage
Volts (V)
A toaster requires 120V & 6A to work. What is its power?
P = I•V
P = (6)•(120)
P = 720 W
The toaster has 720 watts of power
An appliance requires 240V & 2A to work. What is its power?
P = I•V
P = (2)•(240)
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?
Tricky Question
An appliance requires 120V & 12A to work. It is used for 900 seconds. How much energy is used?
P = I•V
P = (12)•(120)
P = 1440 W
Tricky Question
E =1,296,000 J
E = P x Δt
= 1440 x 900
An appliance uses 225V & 4A to work. It is used for 1 hour. How much energy is used?
P = I•V
P = (4)•(225)
P = 900 W
Tricky Question
E =3,240,000 J
60min x 60
E = P x Δt
= 900 x 3600