Heat By Neil Bronks By Neil Bronks
Expansion Atoms vibrate more at higher temperature Zero Kelvin ( C) 200 Kelvin (-73 0 C) 400 Kelvin (127 0 C)
Expansion This makes objects take up more volume Zero Kelvin 200 Kelvin 400 Kelvin
Ball and ring Proves solids expand when heated
Solids Expansion can damage railway lines
Expansion Joints on Bridges
Bi-Metallic Strip The bottom metal expands more than the top strip. It bends! Used to control Gas Oven The bottom metal expands more than the top strip. It bends! Used to control Gas Oven
Bi-Metallic Strip The bottom metal expands more than the top strip. It bends! Used to control Gas Oven The bottom metal expands more than the top strip. It bends! Used to control Gas Oven
Liquids Use to measure temperature as liquid expands up a tube
Gas Expands a lot with a small temperature rise
Heat Transfer Conduction -Transfer by vibrations Radiation -Transfer by Electro-magnetic wave Convection -Hot air rising carrying the heat up with it.
Conduction In a solid every atom is physically bonded to its neighbours in some way. If heat energy is supplied to one part of a solid, the vibration travels through the solid. Conduction is the transfer of energy through matter from particle to particle. It is the transfer and distribution of heat energy from atom to atom within a substance.
Internet Conduction
Practical Conduction A spoon in a cup of hot soup becomes warmer because the heat from the soup is conducted along the spoon. Conduction is most effective in solids It is also why stone and metals appear cold. They are just good conductors. A spoon in a cup of hot soup becomes warmer because the heat from the soup is conducted along the spoon. Conduction is most effective in solids It is also why stone and metals appear cold. They are just good conductors. Chilly
Water as a Poor Conductor HEAT The ice does not melt as the water is a terrible conductor and convection only works up. Metal Gauze ICE Test Tube of water
ConvectionConvection Most houses have radiators to heat their rooms. This is a bad name for them - as they give off heat mainly by convection! The air expands and is less dense so it rises It then cools and falls CONVECTION CURRENT
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Example of convection current Sea Breezes HOT LAND WARM SEA Day – On Shore
Sea Breeze Night COLD LAND WARM SEA Night – Off Shore
Ventilation with convection
Mine Ventilation Demo
RadiationRadiation The transfer of heat in the form of an electro-magnetic wave. Only form of heat that can travel through a vacuum The transfer of heat in the form of an electro-magnetic wave. Only form of heat that can travel through a vacuum
A silver or white body are good at holding and reflecting heat. Black bodies are good at radiating and absorbing heat.
Insulation Vacuum stops heat loss by conduction and convection Silver prevents heat loss by radiation Vacuum stops heat loss by conduction and convection Silver prevents heat loss by radiation
Latent Heat When something boils it takes in heat to change state Its temperature does not rise. Latent heat just changes state When something boils it takes in heat to change state Its temperature does not rise. Latent heat just changes state
Heating a solid Temperature Time Melting point Boiling point
Heating a solid Temperature Time Boiling point Melting point Melting Solid Boiling Liquid Gas Heat raises temperature Latent Heat Only
Sweat Our sweat evaporates and takes heat from our bodies Liquid sweat takes heat from skin as it turns to vapour Our sweat evaporates and takes heat from our bodies Liquid sweat takes heat from skin as it turns to vapour
Uses of Latent Heat Perspiration-Liquid evaporates to gas takes heat from our skin Boiling or Melting matter Refrigeration-liquid boils to take heat from food Heat Pumps- reverse of refrigerator Latent heat is heat that changes state Perspiration-Liquid evaporates to gas takes heat from our skin Boiling or Melting matter Refrigeration-liquid boils to take heat from food Heat Pumps- reverse of refrigerator Latent heat is heat that changes state
The Fridge
The Refrigerator Compressor LiquidG as Liquid boils and takes in Latent Heat from the food Gas turns back into a liquid giving out heat
Summary ConductionConvectionRadiation Particles vibrate and transfer their heat to the next particle Particles move and bring their heat with them Heat transferred without the need of a medium (waves)
Summary Water a poor conductor Black good emitter and absorber Silver and white a good reflector and insulator Latent Heat is the heat lost or gained as a material changes state – e.g. sweat Expansion is the volume change in solids liquids and gases. Water a poor conductor Black good emitter and absorber Silver and white a good reflector and insulator Latent Heat is the heat lost or gained as a material changes state – e.g. sweat Expansion is the volume change in solids liquids and gases.
H/W P336 1,2,5,7,8,9,10,11,12,13