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Machines change energy from one form to another
Device Input energy
Output energy
Dynamo
Solar cell
Catapult
Bulb
kinetic electrical
light electrical
elastic kinetic
electrical light
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More…
Device Input energy
Output energy
Microphone
Loudspeaker
Pendulum
Motor
sound electrical
electrical sound
gravitational kinetic
electrical kinetic
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Device Input energy
Output energy
Kettle
Wind-up car
Coal fire
Fan
electrical heat
elastic kinetic
chemical heat
electrical kinetic
More…
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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 always ______.
In what two forms is energy usually wasted?
1._________
2._________Sound
Heat
wasted
If you can hear a device that is not designed to make noise then energy is wasted as sound.
If a device gets warm and it is not designed to get warm then energy is wasted as heat.
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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?
_____________
_____________
_____________
_____________
_____________
_____________
_____________
_____________
Computer
Turbine
Motor
Transformer
Any electrical device
Television
Radio
Car engine
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What happens to wasted energy?
Wasted e_____ spreads out (d_______) into the s_________.
This makes the energy harder to r____.
Remember energy can not be c______ or d_______.
What happens to the wasted energy you get whenever energy is changed from one form to another?
This is why it is important to r_____ the amount of wasted energy there is.
reated estroyed
nergy issipatedurroundings
e-use
educe
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Television
electrical
light
sound
heat
What are the main energy transfers for a television (don’t forget the wasted energy)?
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Car engine
chemical
kinetic
sound
heat
What are the main energy transfers for a car engine (don’t forget the wasted energy)?
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Radio
electrical
sound
heat
What are the main energy transfers for a radio (don’t forget the wasted energy)?
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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%.
There is a formula that allows you to calculate the efficiency of a device or of a process.
Energy efficient light bulbs are more efficient than normal light bulbs because they w____ less energy, and more of the e______ energy that they are supplied with is converted into l___ energy and not h___.
astelectrical
ight eat
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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?
b) In what form is the energy wasted?
c) What is the efficiency of the bulb?
Efficiency = Useful
Total
= 45J/100J
= 0.45 or 45%
55J
heat
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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?
b) In what form is the energy wasted?
c) What is the efficiency of the radio?
Efficiency = Useful
Total
= 96J/300J
= 0.32 or 32%
204J
heat
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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?
b) How much useful energy do you get?
Efficiency = Useful
Total
Useful = Efficiency x total
= 0.65 x 2 000J
= 1 300J
Light and sound
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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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In what form is energy wasted for all electrical devices?
A. Heat
B. Electrical
C. Sound
D. Light
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