P1 – Energy for the P1 – Energy for the homehome

Revision lesson 1Revision lesson 1

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Temperature and heatTemperature and heat

TemperatureTemperature is a measurement of is a measurement of hotnesshotness..The temperature of an object is The temperature of an object is measured in degrees celsius measured in degrees celsius ((°C).°C).

HeatHeat is a measurement of the is a measurement of the energyenergy of an objectof an objectHeat energy is measured in Joules Heat energy is measured in Joules (J)(J)

CompleteComplete cool high higher low quicker thermograms cool high higher low quicker thermograms

warm warm coldcold warmwarm Hot objects have a __________ temperature and usually Hot objects have a __________ temperature and usually

__________ down.__________ down. Cold objects have a __________temperature and usually Cold objects have a __________temperature and usually

__________ up.__________ up. Energy will flow from a hotter object to a colder one.Energy will flow from a hotter object to a colder one. The greater the temperature difference, the faster the rate The greater the temperature difference, the faster the rate

of cooling will be. For eg. A hot cup of coffee would cool of cooling will be. For eg. A hot cup of coffee would cool down faster in a _______room than in a ______ roomdown faster in a _______room than in a ______ room

____________________ are pictures in which colour is used to ____________________ are pictures in which colour is used to represent temperature.represent temperature.

For warm objects, the __________ the temperature, the For warm objects, the __________ the temperature, the __________ they cool.__________ they cool.

Specific heat capacitySpecific heat capacity The amount of energy needed to raise the temperature of somethingThe amount of energy needed to raise the temperature of something depends depends

on:on:How much there is (mass)How much there is (mass)The temperature riseThe temperature riseWhat it is (specific heat capacity)What it is (specific heat capacity)EnergyEnergy = = mass mass x x specific heat capacityspecific heat capacity x x temperature change temperature change Calculate the energy transferred when 80kg of water is heated from 10oC to 25oC.Calculate the energy transferred when 80kg of water is heated from 10oC to 25oC.80 x 4200 x (25-10) = 5 040 000 J80 x 4200 x (25-10) = 5 040 000 JSHC = how much energy something can store. The specific heat capacity of water SHC = how much energy something can store. The specific heat capacity of water

is high therefore is high therefore once heated once heated it stores alot of energy, so its used for central it stores alot of energy, so its used for central heatingheating

Remember water has a higher SHC than most things so it can take more heat Remember water has a higher SHC than most things so it can take more heat energy (time) to increase its temperatureenergy (time) to increase its temperature

Specific latent heatSpecific latent heatSpecific latent heat is the energy needed to Specific latent heat is the energy needed to change change the state the state of 1kg of a substance without changing its of 1kg of a substance without changing its temperaturetemperature

Specific latent heat water to stem Specific latent heat water to stem = 2 260 000 j/kg= 2 260 000 j/kgEnergy = mass x specific latent heatEnergy = mass x specific latent heatCalculate the energy transferred when 1.5kg of water in Calculate the energy transferred when 1.5kg of water in

a kettle changes from liquid to a gas at 100oC.a kettle changes from liquid to a gas at 100oC.1.5 x 2 260 000 = 3 390 000J1.5 x 2 260 000 = 3 390 000JEnergy needed to change state, its different for all Energy needed to change state, its different for all

different materialsdifferent materials

EnergyMass x SLH

Time/s

150

100

50

0

-50

heating

Meltingpoint

Boiling point

heating

solid

liquid

gas

This flat line shows where energy is being used to break the intermolecular bonds for evaporation

This flat line shows where energy is being used to break bonds – this has to be done during melting

Energy is put into break intermolecular bonds

Heat transferHeat transfer

Heat can transfer in one of three Heat can transfer in one of three ways:ways:

ConductionConduction Convection Convection RadiationRadiation

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 __________).

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.

ConductionConduction

Words – vibrations, electrons, solid, heated, better

Heating a non-metal

Heating a metal

How does a cavity wall prevent heat loss from a home?1. H____ energy reaches the interior wall

2. The heat energy is c_______ through the wall

3. The air cavity between the two walls acts as an i_______ and reduces heat loss by c_______ .

Cavity WallsCavity Walls

ConductionConduction

eat

onducted

nsulatoronducti

on

© Boardworks Ltd 200511 of 31

Side-view of double glazing

insulating layer of air

Double glazing keeps a house warmer because there is a layer of a__ between the panes of glass.

Air is a poor c________, so it acts like an i_______, .

The trapped air r_______ heat loss by c_________ from a house.

ir

onductornsulator

educesonduction

Double glazing

How does double glazing keep a house warmer?

Convection – Key IdeasConvection – Key Ideas Heat transfer through liquids and Heat transfer through liquids and

gasesgases Heat causes particles in a fluid to: Heat causes particles in a fluid to:

move apart move apart → less dense → lighter → less dense → lighter → rises (and replace by cooler → rises (and replace by cooler fluid)fluid)

Insert the Missing WordsInsert the Missing Words

heat1. As the water is ______ it becomes

less dense and _____

2. On reaching the surface, the water _____

when in contact with the air

3. As the water cools it becomes more ______ and

sinks

4. A cycle develops whereby warm water rises and cool water sinks, we call this a

__________ current

heated rises

cools

dense

convection

ConvectiConvectionon

Radiation – key factsRadiation – key facts All hot objects radiate heat.All hot objects radiate heat. Called infra-red radiationCalled infra-red radiation Dull, dark surfaces are the best Dull, dark surfaces are the best

radiators and absorbers of heatradiators and absorbers of heat Pale, shiny surfaces are the worst Pale, shiny surfaces are the worst

radiators and absorbers of heatradiators and absorbers of heat Infra–red radiation can travel Infra–red radiation can travel

through a vacuumthrough a vacuum

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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 ___.

RadiationRadiation

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 Reduce energy loss from homeshomesRoof - 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

Home insulationHome insulation We can reduce the heat losses from our homes in We can reduce the heat losses from our homes in

many ways. Unscramble the list below to find out the many ways. Unscramble the list below to find out the ways:ways:

bouled zgnlagibouled zgnlagivytiac llaw sunatoinilvytiac llaw sunatoinilDrghaut xluecderDrghaut xluecderfotl sunatoinilfotl sunatoinilarcetpsarcetpsurctansiurctansi

Why do each of these methods work? Why do each of these methods work? Describe which method of heat transfer they reduceDescribe which method of heat transfer they reduce

6 marker question6 marker questionEnergy 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. 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.

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 EfficiencyPayback and Efficiency Payback time is the time it takes for Payback time is the time it takes for

an insulation to pay for itselfan insulation to pay for itself Payback time = Payback time = Cost of Cost of

improvementimprovement saving per yearsaving per year

Efficiency = Efficiency = useful energy outuseful energy out total energy intotal energy in

e

output

input

Payback and Efficiency Payback and Efficiency questionsquestions

1.1. Dan spends £120 on loft insulation. He is told that this will Dan spends £120 on loft insulation. He is told that this will reduce his bill by £40 per year. Calculate the payback time.reduce his bill by £40 per year. Calculate the payback time.

2.2. What is payback time?What is payback time?2.2. Dan heats his house with coal fires. He is told that his fires are Dan heats his house with coal fires. He is told that his fires are

32% efficient. Explain what this means.32% efficient. Explain what this means.3.3. A kettle gives out 80J of heat to the room, and is supplied with A kettle gives out 80J of heat to the room, and is supplied with

180 J of energy. How efficient is the kettle?180 J of energy. How efficient is the kettle?4.4. 120/40 = 3years120/40 = 3years5.5. How long it will take the cost of the item to start saving on 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. energy bills .Its the cost of insulation divided by annual saving. 3. How much useful energy is supplied from a device3. How much useful energy is supplied from a device4. 180-80 = useful = 100J4. 180-80 = useful = 100J

100/180 = 0.56 J 100/180 = 0.56 J

Plenary - To DoPlenary - To DoMake flash cards for:Make flash cards for:

Heat and temperatureHeat and temperature Specific heat capacity and Specific latent heatSpecific heat capacity and Specific latent heat Heat transfer (conduction, convection and Heat transfer (conduction, convection and

radiation)radiation) Reducing energy losses from the homeReducing energy losses from the home Payback and efficiencyPayback and efficiency

Now use them to test a partnerNow use them to test a partner