Transcript File

5.10 Energy and Power


Energy (E)
 the ability to do work
 Measured in Joules (J)
Power (P)
 the amount of work that can be
accomplished in a certain amount of
time
 Measured in Watts (W)
Energy
the ability to do work
 all appliances need energy to work


ex.

ex.
a hair dryer needs to be plugged
in to get energy to work
a remote control needs energy
from batteries to work
Power
the rate at which energy is used or
the amount of work done per
second
 Is measured in Watts

A
microwave that uses more Watts
will heat food faster!
Symbols and Units
Symbol =
Symbol =
Units
Units
=
=
E = P x Δt
Time
Energy
Joules (J)
Power
Watts (W)
Seconds (s)
A stereo has a power rating of 200W &
is used for 1800 seconds. How much
energy is used?
E = P x Δt
= 200 x 1800
E = 360 000J
A video game has a power rating of
175W & is used for 3600 seconds.
How much energy is used?
E = P x Δt
= 175 x 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 x Δt
= 425 x 600
E = 255,000 J
Time must be in seconds
10 min x 60 = 600
seconds
255,000 Joules of energy
were used to work the
hair dryer
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)
Voltage
Current
Amps (A)
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?
An appliance requires 120V & 12A to work.
It is used for 900 seconds.
How much
energy is used?
E = P x Δt
P = I•V
P = (12)•(120)
P = 1440 W
= 1440 x 900
E =1,296,000 J
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
E = P x Δt
60min x 60
= 900 x 3600
E =3,240,000 J