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KS4 Energy transfers and Efficiency

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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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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%