Transcript P1 – Energy for the home

P1 – Energy for the
home
Revision lesson 1
Revision Lessons
Does not contain all of the content for P1 – use checklists
..\P1 Energy for the home 2011\Summary and
Checklists\P1 Checklist Foundation.doc
..\P1 Energy for the home 2011\Summary and
Checklists\P1 Checklist Higher.doc
09/04/2015
Temperature and heat
Temperature is a measurement of
hotness.
The temperature of an object is
measured in degrees celsius (°C).
Heat is a measurement of the energy of
an object
Heat energy is measured in Joules (J)
Complete
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cool
warm
high higher
low quicker thermograms
cold
warm
Hot objects have a __________ temperature and usually
__________ down.
Cold objects have a __________temperature and usually
__________ up.
Energy will flow from a hotter object to a colder one.
The greater the temperature difference, the faster the rate
of cooling will be. For eg. A hot cup of coffee would cool
down faster in a _______room than in a ______ room
____________________ are pictures in which colour is
used to represent temperature.
For warm objects, the __________ the temperature, the
__________ they cool.
Specific heat capacity
The amount of energy needed to raise the temperature of
something depends on:
How much there is (mass)
The temperature rise
What it is (specific heat capacity)
Energy = mass x specific heat capacity x temperature change
Calculate the energy transferred when 80kg of water is
heated from 10oC to 25oC.
80 x 4200 x (25-10) = 5 040 000 J
SHC = how much energy something can store. The specific
heat capacity of water is high therefore once heated it
stores alot of energy, so its used for central heating
Remember water has a higher SHC than most things so it can
take more heat energy (time) to increase its temperature
Specific latent heat
Energy
Mass x SLH
Specific latent heat is the energy needed to change
the state of 1kg of a substance without changing its
temperature
Specific latent heat water to stem
= 2 260 000 j/kg
Energy = mass x specific latent heat
Calculate the energy transferred when 1.5kg of water
in a kettle changes from liquid to a gas at 100oC.
1.5 x 2 260 000 = 3 390 000J
Energy needed to change state, its different for all
different materials
Energy is put into break intermolecular bonds
150
This flat line shows where
energy is being used to break
the intermolecular bonds for
evaporation
100
50
Melting
point
0
solid
heating
-50
gas
Boiling
point
liquid
heating
Time/s
This flat line shows where
energy is being used to break
bonds – this has to be done
during melting
Heat transfer
Heat can transfer in one of three
ways:
 Conduction
 Convection
 Radiation
Conduction
Conduction is all about when heat is transferred through a
_________. The heat is passed on by ___________ in the
molecules. These vibrations get BIGGER when the solid has
more ENERGY (i.e. when it is being __________).
Heating a non-metal
Heating a metal
Metals are _______ conductors than non-metals. This is
because the heat is carried by free ________ that can
carry the energy around the metal and give it to other
electrons and ions.
Words – vibrations, electrons, solid, heated, better
Conduction
Cavity Walls
How does a cavity wall prevent heat loss from a home?
eat energy reaches the interior wall
1. H____
onducted through the wall
2. The heat energy is c_______
nsulator and
3. The air cavity between the two walls acts as an i_______
reduces heat loss by c_______
onduction .
Double glazing
How does double glazing keep a house warmer?
Double glazing keeps a house
warmer because there is a layer of
ir between the panes of glass.
a__
onductor so it acts
Air is a poor c________,
like an i_______,
nsulator .
educes heat loss
The trapped air r_______
onduction from a house.
by c_________
Side-view of double
glazing
11 of 31
insulating layer
of air
© Boardworks Ltd 2005
Convection – Key Ideas
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Heat transfer through liquids and
gases
Heat causes particles in a fluid to:
move apart → less dense → lighter
→ rises (and replace by cooler fluid)
Convection
Insert the Missing Words
2. On reaching the surface,
cools when in
the water _____
contact with the air
3. As the water cools
it becomes more
dense and sinks
______
heat
4. A cycle develops whereby
warm water rises and cool
water sinks, we call this a
convection current
__________
1. As the water is
heated it becomes
______
rises
less dense and _____
Radiation – key facts
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All hot objects radiate heat.
Called infra-red radiation
Dull, dark surfaces are the best
radiators and absorbers of heat
Pale, shiny surfaces are the worst
radiators and absorbers of heat
Infra–red radiation can travel
through a vacuum
Radiation
09/04/2015
Radiation is when heat moves around in electromagnetic _________ like light
does. Any hot object will emit heat radiation – the hotter it is, the more radiation
it emits. This type of radiation is called __________, and too much of it will
cause _________. Dark, matt colours will absorb AND emit the _____ infra-red
radiation, and light, shiny colours will ________ it.
The main difference with radiation is that conduction and convection could
ONLY happen in solids, liquids or gases, whereas radiation will happen through
an _____ _____. This is just as well, as otherwise we wouldn’t be able to get
any heat from the ___.
Words – sun, reflect, infra-red, waves, most, empty space, sunburn
Anything HOT emits HEAT RADIATION – the hotter it is,
the more infra red radiation it emits
Thought shower: Where can heat be lost from your home?:
Obviously, insulating your home can be quite expensive.
Reduce energy loss from homes
Roof - insulate loft; reduce conduction
through ceiling and convection in loft space •
 Walls - cavity wall insulation; reduce
conduction, convection, radiation (if shiny)
 Windows - double glazing; reduce
conduction, convection if vacuum or gas at
low pressure
 Doors - draught excluder; reduce
conduction, convection
 Floors - carpets; trapped air pockets in
wool are good insulators they reduce
conduction
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Home insulation
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We can reduce the heat losses from our homes in many
ways. Unscramble the list below to find out the ways:
bouled zgnlagi
vytiac llaw sunatoinil
Drghaut xluecder
fotl sunatoinil
arcetps
urctansi
Why do each of these methods work?
Describe which method of heat transfer they reduce
Describe how energy is lost through the wall from the inside to the outside and how the insulation reduces the different types of energy loss.
! The quality of written communication will be assessed in your answer to this question.
6 marker question
Energy losses in the home can be
reduced by energy saving measures.
One measure is to have double-glazed
windows which reduce the amount of
heat lost by conduction. The gap
between the two pieces of glass is
usually filled with a gas or a vacuum
Describe how energy is lost through the wall from the
inside to the outside and how the insulation reduces the
different types of energy loss.
! The quality of written communication will be assessed
in your answer to this question
Payback and Efficiency
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Payback time is the time it takes for
an insulation to pay for itself
Payback time = Cost of improvement
saving per year
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Efficiency =
output
e
input
useful energy out
total energy in
Payback and Efficiency
questions
Dan spends £120 on loft insulation. He is told that this
will reduce his bill by £40 per year. Calculate the
payback time.
2.
What is payback time?
2. Dan heats his house with coal fires. He is told that his
fires are 32% efficient. Explain what this means.
3.
A kettle gives out 80J of heat to the room, and is
supplied with 180 J of energy. How efficient is the
kettle?
1.
120/40 = 3years
2.
How long it will take the cost of the item to start saving
on energy bills .Its the cost of insulation divided by
annual saving.
3. How much useful energy is supplied from a device
4. 180-80 = useful = 100J
100/180 = 0.56 J
1.
Plenary - To Do
Make flash cards for:
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Heat and temperature
Specific heat capacity and Specific latent heat
Heat transfer (conduction, convection and
radiation)
Reducing energy losses from the home
Payback and efficiency
Now use them to test a partner