Methods of Heat Transfer

Conduction

The process through which heat is transferred within an object , when a temperature difference is present between 2 regions of a metal  is known as conduction .

• In short, transfer of heat from the hot end to the cold end of solid objects is known as conduction .
• Materials that allow heat to pass through them easily are known as conductors .
• For example - Copper , Iron (and other metals )
• Materials that do not allow heat to pass through them easily are known as insulators .
• For example - Rubber , Wood .
• Conduction is involved in the transfer of heat from one end of a pan handle to the other end , which turns hot even though there is no flame under it. 

Convection

The process by which heat is transferred in fluids is known as convection .

• When fluid (water) near the flame is heated, it rises from the bottom and cold water rushes in from the sides to fill in the gap. 
• As this water also gets heated, more cold water rushes in from the sides to fill in the gap, until heat is dissipated through the entire fluid .
• This phenomenon is also seen in other fluids such as air .

Radiation

The process by which heat is transferred without the presence of a medium (solid or fluid) is known as Radiation .

• It can take place whether the medium is present or not .
• All bodies radiate heat. 
• Some of this radiated heat is absorbed by the surroundings (making it hotter).
• Some of it is transmitted  (passes) through the surroundings.
• The rest is reflected by the surfaces it comes into contact with.

For example - 

• When the pan is taken away from the flame, it transfers heat to the surrounding by radiation .
• Similarly, the heat from a heater during winters reaches us by radiation .