KS4 Energy transfers
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Transducers change energy from one form
to another
Device
Input
energy
Output
energy
Dynamo
kinetic
electrical
Solar cell
light
electrical
Catapult
elastic
kinetic
Bulb
electrical
light
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Transducers 2:
Device
Input
energy
Output
energy
Microphone
sound
Loudspeaker
electrical
sound
Pendulum
gravitational
kinetic
Motor
electrical
kinetic
electrical
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Transducers 3:
Device
Input
energy
Output
energy
Kettle
electrical
heat
Wind-up car
elastic
kinetic
Coal fire
chemical
heat
Fan
electrical
kinetic
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Transferring energy
“Energy can neither be created or destroyed,
just changed in form.”
You need to be able to give examples of
devices that perform specific energy
changes.
You need to be able to describe the
energy changes for a given device.
You need to remember that whenever energy is
changed from one form to another, some
energy is always wasted.
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Wasted energy
You need to remember that whenever energy is
changed from one form to another, some energy is
wasted
always ______.
In what two forms is energy usually wasted?
Heat
1._________
Sound
2._________
If a device gets warm and it is not designed to get
warm then energy is wasted as heat.
If you can hear a device that is not designed to make
noise then energy is wasted as sound.
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Wasted sound energy
Can you name some devices that waste energy as sound?
Hairdryer
_____________
Washing machine
_____________
Car engine
_____________
Computer
_____________
Microwave
_____________
Bunsen burner
_____________
Wind turbine
_____________
Dish washer
_____________
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Wasted heat energy
Can you name some devices that waste energy as heat?
Radio
_____________
Television
_____________
Car engine
_____________
Computer
_____________
Turbine
_____________
Motor
_____________
Transformer
_____________
Any
electrical device
_____________
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What happens to wasted energy?
What happens to the wasted energy you get whenever
energy is changed from one form to another?
estroyed
Remember energy can not be c______
reated or d_______.
Wasted e_____
nergy spreads out (d_______)
issipated into the
s_________.
urroundings
This makes the energy harder to r____.
e-use
This is why it is important to r_____
educe the amount of
wasted energy there is.
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Television
What are the main energy transfers for a television
(don’t forget the wasted energy)?
light
electrical
sound
heat
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Car engine
What are the main energy transfers for a car engine
(don’t forget the wasted energy)?
kinetic
chemical
sound
heat
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Radio
What are the main energy transfers for a radio
(don’t forget the wasted energy)?
sound
electrical
heat
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Efficiency
Efficiency is a measure of how good
a device is at changing energy from
one form to another.
All devices waste energy, so the
efficiency of a device is never 100%.
Energy efficient light bulbs are more efficient than normal
aste less energy, and more
light bulbs because they w____
lectrical energy that they are supplied with is
of the e______
ight energy and not h___.
converted into l___
eat
There is a formula that allows you to calculate the
efficiency of a device or of a process.
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The efficiency formula
We can express efficiency mathematically using the
equation:
Efficiency
=
Useful energy out
Total energy in
The efficiency formula is unusual because it has no units.
It is a number between 0 and 1 or a percentage.
Useful energy measured in Joules (J)
Total energy measured in Joules (J)
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Efficiency for a bulb
If you have a filament
bulb and it is supplied
with 100J of electrical
energy which it converts
to 45J of light energy.
a) How much energy is
wasted? 55J
b) In what form is the
energy wasted? heat
c) What is the efficiency of
the bulb?
Efficiency
= Useful
Total
= 45J/100J
= 0.45 or 45%
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Efficiency for a radio
If you have a radio and
it is supplied with 300J
of electrical energy
which it converts to 96J
of sound energy.
a) How much energy is
wasted? 204J
b) In what form is the
energy wasted? heat
c) What is the efficiency of
the radio?
Efficiency
= Useful
Total
= 96J/300J
= 0.32 or 32%
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Efficiency for a TV
If you have a television
and it converts 2 000J
of electrical energy into
useful energy at an
efficiency of 65%,
a) What useful energy do
get from a TV?
Light and sound
b) How much useful
energy do you get?
Efficiency = Useful
Total
Useful = Efficiency x total
= 0.65 x 2 000J
= 1 300J
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Falling objects
When an object falls in a gravitational field:
Gravitational Potential Energy (GPE) at
the top equals the Kinetic Energy (KE) of
the object just before it hits the ground.
Assuming no
energy is lost
by air
resistance!!!

So if a diver has 4 000J of
GPE on top of a cliff, how
much KE will she have just
before she hits the sea?
4 000J
_________
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In which two forms is energy usually wasted?
A. Sound and light
B. Heat and sound

C. Heat and light
D. Light and chemical
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What is the intended energy transfer for a
Bunsen burner?
A. Sound  light
B. Heat  chemical
C. Chemical  light
D. Chemical  heat

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What is the energy change for a falling rock?
A. Kinetic  gravitational
B. Gravitational  kinetic

C. Kinetic  speed
D. Mass  speed
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In what form is energy wasted for all electrical
devices?
A. Heat

B. Electrical
C. Sound
D. Light
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If a plant converts 200J of light energy into 140J
of chemical energy by photosynthesis, what is
the efficiency of the process?
A. 30J
B. 30%
C. 70J
D. 70%

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