Transfer of Thermal Energy Chapter Notes | Physics for GCSE/IGCSE - Year 11 PDF Download

 Page 1


Thermal energy transfers
? Main types of heat transfers
? Conduction
? Convection
? Radiation
? Heat is the transfer of energy from objects of different temperatures
? As objects warm up or cool down, their kinetic energy changes
? Conduction
? It is the process by which heat or energy is directly transmitted through a substance
when there is a difference in temperature between the 2 substances
? Conductor - it lets heat and energy transmit through it
? Insulator - it doesn't let heat and energy transmit through it
? Metals are better conductors as they have a lot of free electrons available
? Convection
? The mode of heat energy transfer that mainly occurs in fluids due to difference in
densities
? Convection current
? It is the movement of a fluid that carries energy from a warmer to a cooler place
? Radiation
? Process of transferring energy by electromagnetic waves
? The hotter the object, the higher frequency of radiation emitted
? It does not require any medium to transfer energy meaning it can transfer across vacuum
? Electromagnetic radiation transfers energy from a hot to a colder region
? Characteristics of infrared radiation
? It is produced by warm or hot objects and is a form of electromagnetic radiation
? Travels through empty space in the form of waves
? Travels in straight lines
? Warms the object that absorbs it
? It is invisible to the naked eye and can only be detected by nerve cells in the skin
? ? Good absorber/bad reflector/best emitter  black and matt
Page 2


Thermal energy transfers
? Main types of heat transfers
? Conduction
? Convection
? Radiation
? Heat is the transfer of energy from objects of different temperatures
? As objects warm up or cool down, their kinetic energy changes
? Conduction
? It is the process by which heat or energy is directly transmitted through a substance
when there is a difference in temperature between the 2 substances
? Conductor - it lets heat and energy transmit through it
? Insulator - it doesn't let heat and energy transmit through it
? Metals are better conductors as they have a lot of free electrons available
? Convection
? The mode of heat energy transfer that mainly occurs in fluids due to difference in
densities
? Convection current
? It is the movement of a fluid that carries energy from a warmer to a cooler place
? Radiation
? Process of transferring energy by electromagnetic waves
? The hotter the object, the higher frequency of radiation emitted
? It does not require any medium to transfer energy meaning it can transfer across vacuum
? Electromagnetic radiation transfers energy from a hot to a colder region
? Characteristics of infrared radiation
? It is produced by warm or hot objects and is a form of electromagnetic radiation
? Travels through empty space in the form of waves
? Travels in straight lines
? Warms the object that absorbs it
? It is invisible to the naked eye and can only be detected by nerve cells in the skin
? ? Good absorber/bad reflector/best emitter  black and matt
? ? Bad absorber/good reflector  white and shiny
? Factors affecting rate of radiation
? Temperature of surface
¦ A hotter surface radiates more energy and emits more radiation than a cooler
surface (directly proportional)
? Surface area
¦ Larger radiation is emitted from a larger surface area. Energy is radiated at a
greater rate from a bigger surface area (directly proportional)
? Consequences of heat energy transfer
? Heat energy travels from a hotter place to a cooler place (high to low temperatures)
? Conduction is the only way that heat energy can travel through a solid. Energy travels
through the solids but the particles cannot move.
? Convection is the main mode of heat energy transfer in fluids. Warm fluid moves around,
carrying energy with it
? Radiation is the only way that the heat energy can travel through vacuum
Home insulation
? Loft insulation(roof)
? Fiberglass is used and air is trapped inside
? This prevents conduction of heat through the roofs
? Underfloor insulation (floor)
? Using the insulating material and carpets to prevent conduction of heat through the floor
? Cavity walls (walls)
? Air is trapped between the 2 layers of bricks, this again prevents conduction of heat
energy through the walls
? When air is removed and there is vacuum between bricks, it prevents conduction and
convection
? Double/triple glazing of windows/thick curtain
? It prevents conduction and convection through the windows
? Filling in the cavity of walls with foam or rockwool
? It prevents conduction and convection through the walls
? Vacuum flask
? No thermal energy transfer by conduction and convection
Page 3


Thermal energy transfers
? Main types of heat transfers
? Conduction
? Convection
? Radiation
? Heat is the transfer of energy from objects of different temperatures
? As objects warm up or cool down, their kinetic energy changes
? Conduction
? It is the process by which heat or energy is directly transmitted through a substance
when there is a difference in temperature between the 2 substances
? Conductor - it lets heat and energy transmit through it
? Insulator - it doesn't let heat and energy transmit through it
? Metals are better conductors as they have a lot of free electrons available
? Convection
? The mode of heat energy transfer that mainly occurs in fluids due to difference in
densities
? Convection current
? It is the movement of a fluid that carries energy from a warmer to a cooler place
? Radiation
? Process of transferring energy by electromagnetic waves
? The hotter the object, the higher frequency of radiation emitted
? It does not require any medium to transfer energy meaning it can transfer across vacuum
? Electromagnetic radiation transfers energy from a hot to a colder region
? Characteristics of infrared radiation
? It is produced by warm or hot objects and is a form of electromagnetic radiation
? Travels through empty space in the form of waves
? Travels in straight lines
? Warms the object that absorbs it
? It is invisible to the naked eye and can only be detected by nerve cells in the skin
? ? Good absorber/bad reflector/best emitter  black and matt
? ? Bad absorber/good reflector  white and shiny
? Factors affecting rate of radiation
? Temperature of surface
¦ A hotter surface radiates more energy and emits more radiation than a cooler
surface (directly proportional)
? Surface area
¦ Larger radiation is emitted from a larger surface area. Energy is radiated at a
greater rate from a bigger surface area (directly proportional)
? Consequences of heat energy transfer
? Heat energy travels from a hotter place to a cooler place (high to low temperatures)
? Conduction is the only way that heat energy can travel through a solid. Energy travels
through the solids but the particles cannot move.
? Convection is the main mode of heat energy transfer in fluids. Warm fluid moves around,
carrying energy with it
? Radiation is the only way that the heat energy can travel through vacuum
Home insulation
? Loft insulation(roof)
? Fiberglass is used and air is trapped inside
? This prevents conduction of heat through the roofs
? Underfloor insulation (floor)
? Using the insulating material and carpets to prevent conduction of heat through the floor
? Cavity walls (walls)
? Air is trapped between the 2 layers of bricks, this again prevents conduction of heat
energy through the walls
? When air is removed and there is vacuum between bricks, it prevents conduction and
convection
? Double/triple glazing of windows/thick curtain
? It prevents conduction and convection through the windows
? Filling in the cavity of walls with foam or rockwool
? It prevents conduction and convection through the walls
? Vacuum flask
? No thermal energy transfer by conduction and convection
? Silvered surfaces
? Inner silvered surfaces reflect radiation from hot fluids back into the flask. Outer
silvered surface reflects radiation in the external surroundings away from the flask.
? Foam plastic support
? Reduce thermal energy transfer by conduction
? Plastic cap
? Reduce thermal energy transfer by conduction, stops convection and evaporation