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Modified over 4 years ago
Heat can travel by Convection A hot fluid expands, so is less dense, so rises. Cold fluid takes its place. A convection current can be formed.
Examples of Convection
Heat cannot travel in solids by convection. Why ?
Heat can travel by Conduction Hot particles vibrate more, so collide with adjacent particles. The heat energy travels from hot to cooler areas. hot cold
Heat can travel by Conduction Metals are good conductors of heat Why ?
Heat can travel by Conduction Metals are good conductors of heat They have free electrons that can move from atom to atom carrying thermal energy too
Heat can travel by Conduction Most gases are poor conductors of heat (insulators) Why ?
Heat can travel by Conduction Gases are poor conductors of heat (insulators) The atoms are too far apart for the vibrations to be passed easily.
There’s one other way! ¡Uno mas!
Heat can travel by infrared radiation (“Hot light”!)
Infrared radiation Infrared radiation can travel through a vacuum (and through air)
An experiment! Can you gather again around Mr Porter?
Infrared radiation Black objects are good absorbers of infrared radiation.
Infrared radiation Shiny objects reflect infrared radiation. Nottingham Forest winning the champions league in 1979
Infrared radiation Black objects are good EMITTERS of IR radiation 100°C Shiny!
Vacuum Flask (“Thermos”)
The insulated lid stops the heat escaping (and entering) by convection
The vacuum between the two walls stops the heat escaping (and entering) by conduction vacuum
The silvered inner and outer stops the heat escaping (and entering) by radiation silvered outer silvered inner
This means hot liquids stay hot because the heat cannot escape Hot chocolate
This means cold liquids stay cold because the heat cannot enter Cold Vimto
In reality, some heat escapes via the lid and eventually the liquid inside will become the same temperature as the surroundings
In a perfect flask without a lid, a hot drink would stay hot forever! Hot chocolate
The vacuum flask Can you complete the sheet please?
Other methods of insulation? Can you think of FIVE other examples of heat insulation? Draw a diagram for each one and two sentences of explanation explaining how it works.
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