ks4 energy - energy transfers-2

5/28/2018 KS4 Energy - Energy Transfers-2

1/33

Boardworks Ltd 20051 of 33

KS4 Physics

Energy Transfers


2/33


Energy Transfers

Useful energy

Conservation of energy

Efficiency

Summary activities

Wasted energy

Contents


3/33


Useful energy transfer

electrical

energy

kinetic

energy

Many everyday objects are designed to transfer energy from

one form into another useful form.

What energy transfer is an electric fandesigned to carry out?


4/33


What is the useful energy transfer?

electrical

energy

sound

energy

What energy transfer is a speakerdesigned to carry out?


5/33



kinetic

energy

electrical

energy

What energy transfer is a wind farmdesigned to carry out?


6/33



gravitational

energy

electrical

energy

What energy transfer is a hydroelectric power station

designed to carry out?


7/33


Useful energy transfers

DeviceInput

energy

Output

energy

kettle

solar cell

catapult

coal fire

light electrical

elastic kinetic

chemical heat

electrical heat

Complete the input and usefuloutput energies for the

devices in this table.


8/33


Energy Transfers

Usefulenergy


Efficiency

Summary activities

Wasted energy

Contents


9/33


Law of conservation of energy

This means that energy never just disappears.

The total amount of energy always stays the same,

i.e. the total input energy = total output energy.

In most energy transfers, the energy is transferred to

several different forms, which may be useful or not useful.

The energy that is transferred to unwanted forms of energy

is wasted.

Allenergytransfersfollowthelawofconservationofenergy:

Energy cannot be created or destroyed,just changed in form.


10/33


Energy transfer in a television

electrical

light

soundheat

An energy transfer diagram shows the input energy and the

output energies for a device. This includes all the useful and

wasted forms of energy.

For example, in a television:


11/33


Energy transfer in a radio

electrical

sound

heat

What are the main energy transfers in a radio?

(Dont forget the wasted energy.)


12/33


Energy transfer in a car engine

chemical

kinetic

soundheat

What are the main energy transfers in a car engine?

(Dont forget the wasted energy.)


13/33 Boardworks Ltd 200513 of 33

Identifying energy transfers



Falling objects

When an object falls in a gravitational field:

If a diver has 4000J of GPE at the top of a cliff,

how much KE will she have just before she hits the sea?

_________4000J

Gravitational potential energy (GPE) at the topequals the kinetic energy (KE) of the object

just before it hits the ground.

Assuming no energy is lost by air resistance!!!



Gerald the Human Cannonball



Energy Transfers

Useful energy


Efficiency

Summary activities

Wasted energy

Contents



Wasted energy

Whenever energy is changed from one form to another,

some energy is alwayswasted.

Energy is usually wasted as:

All electrical devices produce a small amount of heat

energy, which is normally wasted.

heat energy;

sound energy.



Wasted sound energy

If you can hear a device that is not designed to make noise

then energy is wasted as sound.

Examples of devices that waste energy as sound include:

washingmachine

car engine

hairdryer

jet engine



Wasted heat energy

If a device gets warm and it is not designed to get warm

then energy is wasted as heat.

Examples of devices that waste energy as heatinclude:

radio

mobile phone

charger

television

car engine

Whi h t f i t d?



Which type of energy is wasted?

Wh t h t t d ?



What happens to wasted energy?

Wasted energy spreads outinto the surroundingsthis is

called dissipatedenergy.

This dissipated energy is too spread out to do useful work

and so cannot be re-used.

(Remember that energy cannot be created or destroyed.)

What happens to the wasted energy produced

whenever energy is changed from one form to another?

This is why it is important to reduce the amount of energy

that is wasted.

C t t



Energy Transfers

Useful energy


Efficiency

Summary activities

Wastedenergy

Contents

E ffi i



Energy 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 light bulbs

because they w____ less energy.More of the e_______ energy that

they are supplied with is converted

into l____ energy and not h___.

astelectrical

ight eat

The more efficient a deviceis the less energy is wasted.

C l l ti ffi i



Calculating efficiency

The efficiency of a device can be calculated using this

formula:

This means that efficiency does not have any units.

It is a number between 0 and 1or a percentage.

Useful energy is measured in joules (J).

Total energy is measured in joules (J).

efficiency =useful energy out

total energy in

Effi i f b lb



Efficiency of a bulb

0.45 or 45%

a) How much energyis wasted?

b) In what form is the

energy wasted?

c) What is the efficiency

of the bulb?

Efficiency= Useful

Total

= 45 J

100 J

= 0.45 or 45%

This filament bulb is

supplied with 100J of

electrical energy whichit converts to 45J of

light energy.

55J

heat

Wasted energy = Total Useful

= 100J 45J

= 55J

Effi i f di



Efficiency of a radio

a) How much energyis wasted?

b) In what form is the

energy wasted?

c) What is the efficiency

of the radio?

This radio is supplied

with 300J of electrical

energy which it convertsto 96J of sound energy.

Efficiency = Useful

Total

= 96 J

300J

= 0.32 or 32%

204J

Wasted energy = Total Useful

= 300J 96J

= 204J

heat

0.32 or 32%

Efficienc of a tele ision



Efficiency of a television

a) What useful energy doesa television produce?

b) How much usefulenergy is produced?

This television converts

2 000J of electrical

energy into useful energyat an efficiency of 65%.

Efficiency = Useful

TotalUseful = Efficiency x Total

= 0.65 x 2000J

= 1300J

light and sound

1300J

Efficiency questions



Efficiency questions

Contents



Energy Transfers

Useful energy


Efficiency

Summary activities

Wastedenergy

Contents

Glossary



dissipated Energy that spreads out into its surroundingsso that it is no longer useful.

efficiency

A measure of how good a device is atchanging energy from one form to another.

energy transfer The process of changing energy fromone form into another.

input energy The energy going into a device.

output energy The forms of energy produced by adevice.

useful energy

Energy in a form that is wanted.

wasted energy Energy in a form that is not wanted oris not used.

Glossary

Anagrams


31/33


Anagrams

Energy transfers summary


32/33


Energy transfers summary

Multiple choice quiz


33/33

Multiple-choice quiz

ks4 energy - energy transfers-2

Documents