Heating and cooling
Upcoming SlideShare
Loading in...5
×
 

Heating and cooling

on

  • 1,982 views

 

Statistics

Views

Total Views
1,982
Views on SlideShare
1,969
Embed Views
13

Actions

Likes
1
Downloads
302
Comments
0

1 Embed 13

http://www.berkeleybda.com 13

Accessibility

Categories

Upload Details

Uploaded via as Microsoft PowerPoint

Usage Rights

© All Rights Reserved

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Processing…
Post Comment
Edit your comment
  • Photo credit: © 2008 Jupiterimages Corporation
  • Photo credit: © 2008 Jupiterimages Corporation
  • Worksheet 1 accompanies this slide. This worksheet guides students through trying this experiment for themselves and provides follow-up questions to reinforce understanding.
  • Teacher notes The stopwatch is speeded up for the glass and ceramic rods, as they take a long time.
  • Photo credit: © 2008 Jupiterimages Corporation
  • Photo credit: © 2008 Jupiterimages Corporation
  • Worksheet 2 accompanies this slide. This role play worksheet suggests how conduction, convection and radiation can be modelled in the classroom.
  • Teacher Notes Here are some discussion points in the cartoon: The Sun – is the source of a great deal of radiated heat energy. The cricketers – by wearing white, the cricketers stay cool and can run around without getting too hot. The goths – wearing black has made them hot, sweaty and miserable. One of them has had enough and ripped off his clothes! Will he be hotter or cooler without them? The white geese – are happily swimming around, as they are not too hot. The brown ducks – have got too hot and are hiding in the shade. The woman with the push chair – is using light-coloured items to protect herself and the child from the sun. Note the difference between her two dogs.
  • Photo credit (making tea thermogram): © TONY MCCONNELL/SCIENCE PHOTO LIBRARY Photo credit (elephant thermogram): © TED KINSMAN/SCIENCE PHOTO LIBRARY Photo credit (naked man thermogram): © DR. ARTHUR TUCKER/SCIENCE PHOTO LIBRARY PHOTO LIBRARY
  • Photo credit: © 2008 Jupiterimages Corporation
  • Photo credit: © 2008 Jupiterimages Corporation
  • Photo credit: Alfred Pasieka / Science Photo Library Thermogram of a house showing the distribution of heat over its surface. The colour coding ranges from white to yellow for the warmest areas (greatest heat loss) through red to purple and green for the coolest areas (greatest insulation). This thermogram shows that the roof and windows (yellow) are poorly insulated, while the walls (red, purple and green) are losing the least heat. Thermograms are often used to check houses for heat loss, so that they can be made more energy efficient through improved insulation.
  • Worksheet 3 accompanies this slide. This worksheet suggests how students can investigate heat loss by attempting to insulate a shoebox.
  • Glossary: conduction – The way that heat travels through solids, which is possible because their particles are close together. conductor – A material that allows heat to flow through it easily. convection – The way that most heat travels through liquids and gases, which is possible because their particles are free to move. emit – To give out energy. heat – A form of energy that moves between objects of different temperatures, measured in joules (J). insulator – A material that does not allow heat to flow through it easily. radiation – The transfer of heat by electromagnetic waves. It is a method of heat transfer in which the heat energy does not need a medium through which to travel. temperature – How hot or cold an object is, measured in degrees Celsius (°C).

Heating and cooling Heating and cooling Presentation Transcript

  • 1 of 45 © Boardworks Ltd 2008
  • 2 of 45 © Boardworks Ltd 2008
  • Ideas about heat 3 of 45 © Boardworks Ltd 2008 View slide
  • What is temperature?Temperature is a measure of how hot or cold an object is.It is determined by the average kinetic energy of the particlesin the object.Temperature is measured in degrees Celsius (°C).  The freezing point of pure water is defined as 0 °C (at sea level).  The boiling point of pure water is defined as 100 °C (at sea level). Temperature can be measured by a variety of different thermometers. These include liquid in glass, digital, thermocouple and bimetallic strip thermometers. 4 of 45 © Boardworks Ltd 2008 View slide
  • What is heat?Heat is the energytransfer that takesplace betweenobjects of differenttemperatures.Heat is measuredin joules (J).How many joulesare there in akilojoule (kJ)?Heat transfer only occurs when there is a temperaturedifference between substances. Heat always moves from anarea of higher temperature to an area of lower temperature. 5 of 45 © Boardworks Ltd 2008
  • Types of heat transferHeat transfer can takeplace in three differentways: conduction, which mainly occurs in solids convection, which only occurs in liquids and gases radiation, which occurs through any material or even through a vacuum. 6 of 45 © Boardworks Ltd 2008
  • The particle modelThe differences between hot and cold objects – andbetween solids, liquids and gases – can be explained bythe particle model. All substances consist of particles (atoms or molecules). The particles are tightly packed in a solid or spaced further apart in a liquid or gas. The particles are attracted to each other; some strongly and others weakly. The particles move around, i.e. they have kinetic energy. The kinetic energy of particles increases with temperature. 7 of 45 © Boardworks Ltd 2008
  • 8 of 45 © Boardworks Ltd 2008
  • Designing a conduction experimentCan you design an experiment to investigate how welldifferent materials conduct heat? Remember to make yourexperiment a fair test to ensure you get reliable results.The available apparatus includes: wax blobs tripod metal, glass and ceramic rods drawing pins Bunsen burner stopwatch 9 of 45 © Boardworks Ltd 2008
  • Investigating conduction 10 of 45 © Boardworks Ltd 2008
  • Conduction in metals and non-metalsIf you touch a piece of wood and a piece of copper metalthat are both at room temperature (about 21 °C), whichmaterial feels warmer?The wood feelswarmer because it isa poor conductor.The wood cannot conduct heat away from your hand asquickly as the copper, which is a good conductor. 11 of 45 © Boardworks Ltd 2008
  • Conduction in non-metals 12 of 45 © Boardworks Ltd 2008
  • Conduction in metalsMetals are good conductorsof heat because: metals contain many free electrons the free electrons can move between atoms at high speed the free electrons carry energy from high-energy atoms to low-energy atoms further away from the heat source. 13 of 45 © Boardworks Ltd 2008
  • Conduction in metals 14 of 45 © Boardworks Ltd 2008
  • Conduction in liquidsMetals are good conductors of heat and almost allnon-metals are poor conductors of heat.Are liquids good at conducting heat? Use some gauze to hold an ice cube at the bottom of a tube of water. Carefully heat the water at the top of the tube only until this water is boiling. If the liquid is good at conducting, the ice should quickly melt – it doesn’t.Liquids are poor conductors of heat (i.e. good insulators). 15 of 45 © Boardworks Ltd 2008
  • Conduction in gasesAre gases good at conducting heat? Carefully hold a safety match 1 cm away from a Bunsen burner flame. (Do not put the match in the flame!) If a gas is a good conductor, the air between the flame and the match should conduct heat and light the match – it doesn’t.Gases are poor conductors of heat (i.e. good insulators). 16 of 45 © Boardworks Ltd 2008
  • Conductor or insulator? 17 of 45 © Boardworks Ltd 2008
  • Convection and densityThe density of a substance depends on how far apart itsparticles are.If water, oil and air are mixedtogether, they will settle out inorder of density. Which onewill rise to the top?The air is least dense andrises to the top. The water isthe most dense and sinks tothe bottom.This is important in explaininghow heat is transferred byconvection. 18 of 45 © Boardworks Ltd 2008
  • Convection currents in a liquidThe movement of hotterareas in a liquid can beseen using potassiumpermanganate as a dye.This cycle is called aconvection current.Can you use the conceptof density to explain howthe convection currentmoves? 19 of 45 © Boardworks Ltd 2008
  • How does convection in a liquid occur? 20 of 45 © Boardworks Ltd 2008
  • Explaining convection 21 of 45 © Boardworks Ltd 2008
  • Convection currents in a coal mineWhen shaft mining was first used to mine coal, convectioncurrents caused by an underground fire were used toventilate the shafts.Why do you think miners don’t use this method anymore? 22 of 45 © Boardworks Ltd 2008
  • 23 of 45 © Boardworks Ltd 2008
  • What is radiation?We know that conduction mainly takes place in solids, andconvection takes place in liquids and gases.How does the Earth receive heat energy from the sunthrough the empty vacuum of space?There is a third kind of heat transfer, which is called radiation,or ‘infra-red radiation’. 24 of 45 © Boardworks Ltd 2008
  • Absorbing radiation 25 of 45 © Boardworks Ltd 2008
  • Seeing infrared radiationThe police and fire service useinfra-red cameras to find peoplein the dark.Infra-red has no colour, but acomputer can put a false colour onthe camera image so we can ‘see’the object.The colours are put on a scalewhich corresponds to temperature.White, yellow and red usuallyrepresent the warmest areas;green, blue and black usuallyrepresent the coolest. 26 of 45 © Boardworks Ltd 2008
  • Infrared goggles 27 of 45 © Boardworks Ltd 2008
  • 28 of 45 © Boardworks Ltd 2008
  • Changes of state activity 29 of 45 © Boardworks Ltd 2008
  • Changes of state – heating curveIf a solid is heated, itstemperature rises until itreaches its melting point.At the melting point, thetemperature stops risingwhile the solid melts,because energy goes intoseparating the particles.Once the solid hasmelted, the temperaturerises again until it reachesthe boiling point. 30 of 45 © Boardworks Ltd 2008
  • Changes of state – heating curveAt the boiling point, the temperature again stays the sameas energy goes into further separating the particles. 31 of 45 © Boardworks Ltd 2008
  • Changes of state – cooling curve 32 of 45 © Boardworks Ltd 2008
  • What is evaporation?Evaporation occurs when the particles in a liquid escapeto form a vapour.Evaporation can take place at any temperature but it occursmost rapidly at a liquid’s boiling point.The particles that escapetake some energy fromthe remaining particles,so the temperature of theliquid falls.Evaporation is anothermethod of heat transfer. 33 of 45 © Boardworks Ltd 2008
  • Evaporation experimentEvaporation from different liquids can be investigatedusing this experiment:1. Take four equal masses of cotton wool and soak each one in a different liquid – ethanol, water, propanol and octanol.1. Wrap each piece of cotton wool around the bottom of a thermometer and secure it with a rubber band.1. Read the temperature every 30 seconds and record the results in a table. 34 of 45 © Boardworks Ltd 2008
  • Evaporation experiment – results Temperature (°C) Temp. Liquid change 0 0.5 1.0 1.5 2.0 2.5 3.0 (°C) min min min min min min min ethanol water propanol octanol 35 of 45 © Boardworks Ltd 2008
  • Evaporation experiment – analysisDraw a bar chart of your results: with temperature change on the y axis, with the type of liquid on the x axis.Plot a line graph of your results: with temperature on the y axis, with time on the x axis, and four lines plotted, one for each liquid.Are any of the results anomalous? 36 of 45 © Boardworks Ltd 2008
  • 37 of 45 © Boardworks Ltd 2008
  • Using thermograms to investigate heat lossThermograms are useful for examining heat lost from a house,as they show the temperature distribution over its surface. The yellow and orange roof and window areas are the warmest – these are the worst insulated parts of the house. The dark wall areas are the coolest – these are the best insulated parts of the house.A poorly insulated house loses more energy and so costsmore to heat. It also means that more pollution, particularlycarbon dioxide, is created in order to heat the house. 38 of 45 © Boardworks Ltd 2008
  • Heat transfer – energy lossWhere is the most heat lost from a poorly insulated house? roof 20% windows 12% walls 36% doors 4% floor 28% 39 of 45 © Boardworks Ltd 2008
  • Examining insulationWhat are the different types of home insulation? insulatingDouble glazing adds an extra layerpane of glass to each window. side-view of air of doubleThis means that there is a glazinglayer of air or a vacuumbetween the two panes.This helps to prevent heatloss by conduction.Loft insulation is plastic foam that contains trapped air and soacts as an insulator to stop conduction of heat through theroof tiles.Draught excluders are hairy or spongy strips which are placedunder doors to prevent the movement of convection currents. 40 of 45 © Boardworks Ltd 2008
  • Examining insulationCurtains reduce heat loss by covering up gaps aroundwindows through which convection currents sometimes pass.Cavity wall insulation involves convectionplacing a layer of plastic foam currentsinsulation in between two layers of in theoutside walls. This prevents heat cavityloss by both conduction andconvection currents.Placing a sheet of shiny foil foam insulationbehind radiators prevents heat preventsradiation reaching the wall and convectionconducting outside. Instead, it is currentsreflected back into the room. 41 of 45 © Boardworks Ltd 2008
  • 42 of 45 © Boardworks Ltd 2008
  • Glossary 43 of 45 © Boardworks Ltd 2008
  • Anagrams 44 of 45 © Boardworks Ltd 2008
  • Multiple-choice quiz 45 of 45 © Boardworks Ltd 2008