0708 conduction convection_radiation


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0708 conduction convection_radiation

  1. 1. Understanding HeatTransfer,Conduction,Convection andRadiation
  2. 2. Heat Transfer• Heat always moves from a warmer place toa cooler place.• Hot objects in a cooler room will cool toroom temperature.• Cold objects in a warmer room will heat upto room temperature.
  3. 3. Question• If a cup of coffee and a red popsicle wereleft on the table in this room what wouldhappen to them? Why?• The cup of coffee will cool until it reachesroom temperature. The popsicle will meltand then the liquid will warm to roomtemperature.
  4. 4. Heat TransferMethods• Heat transfers in three ways:–Conduction–Convection–Radiation
  5. 5. ConductionWhen you heat a metal strip at one end, the heattravels to the other end.As you heat the metal, the particles vibrate, thesevibrations make the adjacent particles vibrate, and so onand so on, the vibrations are passed along the metal andso is the heat. We call this? Conduction
  6. 6. Metals are differentThe outer e______ of metal atomsdrift, and are free to move.When the metal isheated, this ‘sea ofelectrons’ gain k_____energy and transfer itthroughout the metal.Insulators, such as w___ and p____, do nothave this ‘sea of electrons’ which is why theydo not conduct heat as well as metals.lectronsineticood lastic
  7. 7. Why does metal feel colder than wood, if theyare both at the same temperature?Metal is a conductor, wood is an insulator. Metalconducts the heat away from your hands. Wooddoes not conduct the heat away from your hands aswell as the metal, so the wood feels warmer thanthe metal.
  8. 8. ConvectionWhat happens to the particles in a liquid or agas when you heat them?The particles spread out andbecome less dense.This effects fluid movement.What is a fluid?A liquid or gas.
  9. 9. Fluid movementCooler, more d____, fluidssink through w_____, lessdense fluids.In effect, warmer liquids andgases r___ up.Cooler liquids and gases s___.ensearmeriseink
  10. 10. Water movementHot waterrisesCoolerwater sinksConvectioncurrentCools at thesurface
  11. 11. Why is it windy at the seaside?
  12. 12. Cold air sinksWhere is thefreezercompartmentput in a fridge?FreezercompartmentIt is put at thetop, becausecool air sinks,so it cools thefood on theway down.It is warmerat thebottom, sothis warmerair rises anda convectioncurrent isset up.
  13. 13. The third method of heat transferHow does heat energy getfrom the Sun to the Earth?There are no particlesbetween the Sun and theEarth so it CANNOTtravel by conduction orby convection.?RADIATION
  14. 14. RadiationRadiation travels in straight linesTrue/FalseRadiation can travel through a vacuumTrue/FalseRadiation requires particles to travelTrue/FalseRadiation travels at the speed of lightTrue/False
  15. 15. Emission experimentFour containers were filled with warm water. Whichcontainer would have the warmest water after ten minutes?Shiny metalDull metalDull blackShiny blackThe __________ container would be the warmest after tenminutes because its shiny surface reflects heat _______ backinto the container so less is lost. The ________ containerwould be the coolest because it is the best at _______ heatradiation.shiny metalradiationdull blackemitting
  16. 16. Absorption experimentFour containers were placed equidistant from a heater. Whichcontainer would have the warmest water after ten minutes?The __________ container would be the warmest after tenminutes because its surface absorbs heat _______ the best.The _________ container would be the coolest because it isthe poorest at __________ heat radiation.dull blackradiationshiny metalabsorbingShiny metalDull metalDull blackShiny black
  17. 17. Convection questionsWhy are boilers placed beneath hot watertanks in people’s homes?Hot water rises.So when the boiler heats the water, and the hot waterrises, the water tank is filled with hot water.Why does hot air rise and cold air sink?Cool air is more dense than warm air, so thecool air ‘falls through’ the warm air.
  18. 18. Radiation questionsWhy are houses painted white in hot countries?White reflects heat radiation and keeps the house cooler.Why are shiny foil blankets wrapped around marathonrunners at the end of a race?The shiny metal reflects the heat radiation from the runnerback in, this stops the runner getting cold.
  19. 19. 1. Which of the following is not amethod of heat transfer?A. RadiationB. InsulationC. ConductionD. Convection
  20. 20. 2. In which of the following arethe particles closest together?A. SolidB. LiquidC. GasD. Fluid
  21. 21. 3. How does heat energy reachthe Earth from the Sun?A. RadiationB. ConductionC. ConvectionD. Insulation
  22. 22. 4. Which is the best surface forreflecting heat radiation?A. Shiny whiteB. Dull whiteC. Shiny blackD. Dull black
  23. 23. 5. Which is the best surface forabsorbing heat radiation?A. Shiny whiteB. Dull whiteC. Shiny blackD. Dull black