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 heatThey 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!
Infrared radiation
Infrared radiation
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 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.