What is Conduction?
Conduction is the transfer of thermal energy without any flow of the material medium.
Metals such as copper and iron are good conductor of heat;
Non-metals such as wood and glass are poor conductor of heat.
Conditions for Conduction:
Conduction takes place from one object to another only under the following two conditions.
Process of conduction
(a) Molecular Vibrations for both metal and non-metal
When one end of the solid is heated, the molecules at the hotter end gain kinetic energy and vibrate faster. These molecules collide with their less energetic neighbouring molecules and transfer some of their energy to them which in turn gain kinetic energy. Heat is then passed from molecule to molecule until it reaches the colder end of the solid. The process will only stop when the temperature of the solid becomes uniform and constant.
It is a rather slow process.
(b) Free electron diffusion for metal only
When a metal is heated, the free electrons gain kinetic energy and move faster. These electrons can move freely in the spaces between molecules before colliding with other electrons or molecules and transfer some energy to them.
Free electron diffusion is a very quick process, much faster than molecular vibration.
Rate of heat transfer via conduction
Solid > liquid > gas
Molecules in solids are more closely packed and hence collisions are more frequent.
Liquids and gases are poor conductor of heat.
(a) Good conductor of heat
The materials which are good conductors of heat are used whenever heat is to be transferred fast.
i.e. cooking utensils are usually made of metals and their alloys.
(b) Poor conductor of heat
The materials which are poor conductors of heat are used to prevent the transfer of heat or minimize the loss of thermal energy.
i.e. handles of the cooking utensils are made of wood or plastics so that even the hot utensils can be lifted safely.
Note that Fibreglass, foam and felt usually trap pockets of air, which are poor conductors of heat.