The transfer of energy by heating processes andPresentation Transcript
The transfer of energy by heatingprocesses and the factorsthat affect the rate at which thatenergy is transferred
Energy can be transferred from one place to another by workor by heating processes. We need toknow how this energy is transferred and which heatingprocesses are most important in a particularsituation.
I can:✓compare ways in which energy is transferred in andout of objects by heating and ways in which therates of these transfers can be variedevaluate the design of everyday appliances thattransfer energy by heating, including economicconsiderationsevaluate the effectiveness of different types ofmaterial used for insulation, including U-valuesand economic factors including payback timeevaluate different materials according to theirspecific heat capacities.
Infrared radiationa) All objects emit (give out) and absorb (take in) infraredradiation.If an object is a good emitter, it will also be a good absorber.b) The hotter an object is the more infrared radiation itradiates (gives out) in a given time.If the object is cooler than its surroundings it will absorb moreheat than it emits, so it will warm up.c) Dark, matt surfaces are good absorbers and good emittersof infrared radiation.d) Light, shiny surfaces are poor absorbers and poor emittersof infrared radiation.e) Light, shiny surfaces are good reflectors of infraredradiation.
P1.1.2 Kinetic theorya) The use of kinetic theory to explain the different states ofmatter.The diagram shows the difference between a solid, liquid and agas.
As a substance is heated the particles will vibratemore and move about more.In a solid the particles are arranged in a tightpattern, they don’t have much energy and so onlyvibrate a littleWhat will happen when a metal bar is heated?
In a solid the particles are arranged in a tightpattern, they don’t have much energy and so onlyvibrate a littleIn a liquid the particles are close together, but canmove past each other.In a gas the particles have much more energy than inliquids or solids, they are free to move in any direction.Heating gives the particles more energy; this will causesolids to melt and liquids to boil.b) The particles of solids, liquids and gases havedifferent amounts of energy.In a liquid the particles are close together, but canmove past each other.
P1.1.3 Energy transfer by heatinga) The transfer of energy byconduction, convection, evaporation andcondensation involves particles,and how this transfer takes place.
b) The factors that affect the rate of evaporation andcondensation.Evaporation is when a liquid turns to a gasCondensation is when a gas turns to a liquid.
c) The rate at which an object transfers energy byheating depends on: surface area and volumethe material from which the object is made thenature of the surface with which the object is incontact.d) The bigger the temperature difference betweenan object and its surroundings, the faster the rate atwhich energy is transferred by heating.
Conductors and insulatorsConduction occurs when particles vibrate and pass ontheir energy to a neighbouring particle.Materials with particles close together conduct heatmuch faster then materials with large spacesbetween particles.Metals are good conductors becauseof their free electrons.The electrons are free to move aroundinside the metal so they transfer theenergy very quickly to other particles.
ConvectionAs air warms up, it expands and so is less dense. Itwill then rise. As it cools it becomes more denseand so will sink.
Sea breezes are also caused by convectioncurrents:
conductionconvectionTraps lots of air [not heat]; air is a good insulator/ poorconductor
Plastic/ glass wallsVacuumInsulating topSilvering/ shiny on either wall
Transfer of energy by wavesIons/ electrons gain kinetic energyEnergy is transferred to cooler parts by free electrons as they diffusethrough the metal and collide with ions
Water particles at the bottom are heatedThe warm water expands (becomes less dense)So the warm water rises and coldwater falls to take its place
Hot water rises [not heat rises]because of convection currentsInside is hotter than outsideHeat transfer by conductionSurround/cover/ insulate tank with goodinsulator
Air is an insulator/ poor conductorConvection stopped foam is an insulator/ poorconductor