energy_efficiency.ppt

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Many household objects are designed to transfer energy

from one form into another useful form.

What is a useful energy transfer?

electr icalenergy

kinet icenergy

What energy transfer is an electr ic fan designed to carry out?




electr icalenergy

soundenergy

What energy transfer are these speakers designed to

carry out?





What energy transfer are wind turb ines in a wind farm

designed to carry out?


kinet icenergy

electr icalenergy




gravitat ionalpo tent ial energy

electr icalenergy

What energy transfer is a hyd roelectr ic power stat ion

designed to carry out?





Useful energy transfers




electr ical

l ight

sound

heat

An energy transfer diagram shows the input and output

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

forms of energy.

Energy transfer in a television

For example, in a televis ion :


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electr icalsound

heat

What are the main energy transfers in a radio ?

(Don’t forget the wasted energy.)

Energy transfer in a radio



chemical

k inet ic

sound

heat

What are the main energy transfers in a car engine ?

(Don’t forget the wasted energy.)

Energy transfer in a car engine



Identifying energy transfers



All the energy transfers

(useful and wasted) that

are associated with a

device can be represented

by a Sankey d iagram .

A Sankey diagram uses

arrows to represent all theoutput energies.

How can we represent energy transfers?

100 J

electr icalenergy(input)

20 J

electr icalenergy(input)

10 J

l ightenergy(output)10 J

heat energy(wasted)

90

Jheat energy(wasted)

10 J

l ightenergy(output)

Energy eff ic ient light bu lb

Filament l ight bu lb

How does the energy use in

these light bulbs compare?

The thickness of each

arrow is proportional to the

amount of energy involvedat that stage.



This means that energy never just ‘disappears’.

The total amount of energy always stays the same,

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

In most energy transfers, the energy is transferred to

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

Energy that is transferred to unwanted forms of energy is

wasted.

All energy transfers follow the law of conservat ion of energy :

Energy cannot be created o r destroyed,

jus t changed in fo rm .

Law of conservation of energy



A falling object loses gravitational

potential energy and gains kinetic

energy. This is an example of the

law o f conservat ion of energy.

If the rollercoaster has 15 000 J of

GPE at the top of the slope, how

much KE will it have gained whenit reaches the bottom?

15 000 J , assuming that no energy

gravi tat ional po tential energy

(GPE) lost equalskinet ic energy (KE) gained

What happens to the energy of falling objects?

is lost by air resistance and friction.



Gerald the Human Cannonball



This cordless drill transfers

chemical energy in the battery

into movement, sound and

heat energy.

Appliances usually waste energy as sound and heat .

How is energy wasted?

The movement energy can be

used to do useful work, but the

sound and heat energy cannot.

Energy that does not do useful

work is called wasted energy.

In fact, all electrical devices produce a small amount of heat

energy when they are used, which is normally wasted.



If a device makes noise but is not designed to make noise,

then energy is being wasted as sound .

Examples of devices that waste energy as sound include:

Which devices waste energy as sound?



If a device gets warm but it is not designed to get warm,

then energy is wasted as heat .

Examples of devices that waste energy as heat include:

Which devices waste energy as heat?



Which type of energy is wasted?



Remember that energy cannot be

created or destroyed.

What happens to the wasted energy produced when energy

is changed from one form to another?

What happens to wasted energy?

For example, the heat and light

energy produced by this light bulb

are too spread out to be reused.

Wasted energy spreads ou t

into the surroundings – this iscalled dissipated energy.

This dissipated energy is too

spread out to do useful work and

so cannot be reused .



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%.

An energy-efficient light bulb is

more efficient than a filament bulb

because it wastes less energy.

The more eff ic ient a device

is the less energy is wasted.

What is energy efficiency?

It converts a greater proportion of

the energy that it is supplied with

into light energy and not heat.



New electrical appliances

display information about

how energy efficient they are.

Why is energy efficiency important?

Appliances that are more efficient need less electricity, and soless fossil fuel needs to be burnt in fossil-fuel power stations.

climate change.

This helps consumers to

identify which appliance will

use the least energy and

cost the least to run.

Energy efficiency is not just

about saving money, it’s

also about saving the planet.

This is important for reducing pollution and the effects of



The energy efficiency of a device can be calculated using

this formula:

Energy efficiency does not have any units.

It is a number between 0 and 1 which can be

converted into a percentage by multiplying by 100.

Useful energy is measured in jou les (J ).

Total energy is measured in jou les (J ).

energy eff ic iency =usefu l outpu t energy

to tal inpu t energy

How is energy efficiency calculated?

C l l h ffi i f b lb



0.45 or 45%

a) How much energy

is wasted?

b ) In what fo rm i s the

energy w asted?

c ) What is the eff ic iency

of the bulb?

Eff ic iency = Useful

Total= 45 J

100 J

= 0.45 or 45%

This filament bulb is supplied

with 100 J of electrical energy,

which it converts to 45 J oflight energy.

55 J

heat

Wasted energy = Total – Useful

= 100 J – 45 J

= 55 J

Calculate the efficiency of a bulb

C l l t th ffi i f di




a) How much energy

is wasted?

b) In what form is the

energy w asted?

c ) What is th e

eff ic iency o f the

radio?

This radio is supplied with

300 J of electrical energy

which it converts to 96 J ofsound energy.


Total= 96 J

300J

= 0.32 or 32%

204 J

Wasted energy = Total – Useful

= 300 J – 96 J

= 204 J

heat

0.32 or 32%

Calculate the efficiency of a radio

C l l t th ffi i f t l i i




a) What useful energy does

a television produce?

b) How much useful

energy is produced?

This television converts

2 000 J of electrical energy

into useful energy at anefficiency of 65%.


TotalUseful = Efficiency x Total

= 0.65 x 2 000 J

= 1 300 J

l ight and sound

1 300 J

Calculate the efficiency of a television

E ffi i l l ti ti it




Energy efficiency calculations – activity




Gl




diss ipated energy – Energy that spreads out into itssurroundings so that it is no longer useful.

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

energy trans fer – The process o f changing energy

f romone form to anoth er.

input energy – The energy go ing in to a device.

ou tput energy – The forms of energy p roduced by a

device.

useful energy – Energy in a form that is wanted.

wasted energy – Energy in a form that is no t wanted

or

is no t used.

Glossary

A




Anagrams

E t f d ffi i




Energy transfers and efficiency – summary

Multiple choice quiz



Multiple-choice quiz

energy_efficiency.ppt

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