Conduction and insulation Flashcards
What is conduction?
The particles in the metal next to the external energy store gains heat and starts to vibrate.
They vibrate next to other particles and pass the heat energy along.
Some materials are better conductors than others.
Generally metals are better.
Examples of good conductors
Metals eg copper, aluminium, iron
Non metals eg graphite
What are insulators?
Materials with low thermal conductivity so energy transfer is as low as possible
Materials which are very poor conductors, are called thermal insulators
Eg wood, cotton, cork, expanded polystyrene are good insulators
Saucepan handles are made of plastic so you don’t burn your hands
What do good conductors need?
How well a material conducts heat depends on how close the particles are together
1 solids are best
2 then Liquids
3 gases are terrible heat conductors
Why are metals good conductors?
They contain lots of electrons that move freely inside the metal.
A metal bar is heated at one end. The electrons vibrate, move faster and collide with other free electrons and transfer energy from the hot part of the metal, the free electrons diffuse with atoms and make them collide more frequently
What are examples of good insulators?
Plastic handles for saucepans or spatulas
Felt for loft insulation
Cotton for oven gloves
Wood for chairs and tables
Aluminium for keeping food warm - good conductor and insulator because heat also reflects
What are the common features of good insulators?
Temperature difference across the material
Thickness of the material
Thermal conductivity of the material
How do you reduce heat transfer?
Thermal conductivity of material must be as low as possible
Be as thick as possible
Explain house loft insulation benefits of fibreglass?
Fibreglass reduces the rate of energy transfer through the roof
Air between fibres helps reduce rate of energy transfer
More layers improves insulation
Explain cavity wall insulation?
Reduces rate of energy transfer though outer walls of house
Cavity = space between 2 layers of brick that make up the wall
Insulation fills the cavity, better insulator than air because it traps air in small pockets reducing rate of energy transfer.
Explain how aluminium foil works?
Between radiator panel and the wall so it reflects heat away into the room
It reduces energy transfer by radiation
How do double glazed windows work?
2 sheets of glass
In between dry air or vacuum so it reduces conduction
The thicker the glass the lower the thermal conductivity
Vacuum also prevents energy transfer by convection
