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Section 4b: thermal energy (conduction (thermal conduction = transfer of…
Section 4b: thermal energy
convection
definition = the transfer of energy through fluids but the upward movement of warmer, less dense regions of fluid
convection current
examples - immersion heater, kettles, radiators, hot water tanks
heated less dense air rises
warmer air replaces cooler air
cool, denser air falls
cool air rises to fill the gap left by rising heated air
radiation
definition = the transfer of energy by infra-red waves
the heat energy travels in straight lines
infra-red waves can travel through a vacuum
can be reflected/absorbed by different materials
-shiny surfaces + white surfaces = good reflectors of thermal radiation
-matt black & dark surfaces = poor reflectors / good absorbers of heat radiation
conduction
thermal conduction = transfer of thermal energy through a substance without the substance moving
metals - good thermal conductors
wood - good thermal insulator
Process
in the hot part of a substance, particles have lots of kinetic energy
they transfer some of them to particles near them
this process repeats/continues throughout the substance
metals process is more rapid, they have free electrons which move easily through the substance
sankey diagrams
Energy inputted
useful energy output
waster energy output
the thickness of the arrow represents the amount of energy
efficiency = useful energy output / total energy input
heat in the home
how heat is lost
through conduction
-walls, windows & doors
through convection
-current in between two walls
windows
-thin glass is a poor thermal conductor
solutions
loft insulation = thick layer of fibre glass wool on loft floor - reduces conduction & radiation
drought proofing = strips of foam & plastic around doors & windows - reduces convection
cavity wall insulation = foam squirted in gaps between bricks - reduces convection, conduction & radiation
thick curtains = reduces conduction & radiation
hot water jacket = fibre glass wall - reduces conduction & radiation
double glazing = two layers of glass - reduces conduction & convection
