Conduction of Heat

what is thermal conduction?

Thermal conduction is the process where energy is transferred by vibrating particles in a substance

describe how thermal conduction occurs

The vibrating particles transfer energy from their kinetic store to the kinetic store of neighbouring particles

describe the direction of the energy transfer

The direction of energy transfer is always from hot to cold

The higher the thermal conductivity of a material….

 the higher the rate of energy transfer by conduction across the material

compare materials with high thermal conductivity to low thermal conductivity materials

Materials with high thermal conductivity heat up faster than materials with low thermal conductivity

what are 3 examples of substances with a high thermal conductivity

• Diamond

• Aluminium

• Graphite

what are 3 examples of substances with a low thermal conductivity

• Air

• Steel

• Bronze

what is an insulator?

An insulator is a substance that is a poor thermal conductor

give three examples of insulators

wool, plastic, wood

what are insulators used to do?

Insulators are used to reduce energy transfers, for example, to keep a house warm or build a soundproof room

why is a woollen jumper worn in winter?

• to retain body heat and keep warm

list three things the energy transfer through a layer of insulating material depends on

• temperature difference across a material

• thickness of a material

• thermal conductivity of a material

how does temperature difference across a material affect the energy transfer through that material?

the greater the temperature difference, the more conduction

how does thickness of a material affect the energy transfer through that material?

the thicker the material, the less energy will be transferred by conduction

how does the thermal conductivity of a material affect the energy transfer through that material?

the higher the thermal conductivity, the more energy will be transferred by conduction

so what do good insulators which keep the energy transfer through them as low as possible have?

• A low thermal conductivity

• Layers that are as thick as possible

what does loft insulation do?

Insulating the loft of a house lowers its rate of cooling, meaning less energy is lost to the outside

what is loft insulation often made out of?

The insulation is often made from fibreglass (or glass fibre)

what is fibreglass/glass fibre made out of and why is it a good insulator?

• a reinforced plastic material composed of woven material with glass fibres laid across and held together

• The air trapped between the fibres makes it a goodinsulator

compare the loft insulation to the roof material

loft insulation has a much lower thermal conductivity than the roof material

how is loft insulation built to make it a good insulator

Several layers of insulation make it very thick and therefore decrease the rate of cooling

explain how are houses in cold countries adapted to the weather (2)

• Houses in cold countries are fitted with cavity wall insulation which is made from blown mineral fibre filled with gas

  • This lowers the conduction of heat through the walls from the inside to the outside