Heat Transfer

Conduction

When we place one end of an iron rod in a fire, the other end also heats up after a while. We say heat has been conducted along the rod from the hot end. Conduction is the process by which heat is transmitted through a medium from one particle to another. The heat is transmitted from the hot to the cold end.

Most metals are good thermal conductors. A metal surface feels colder than a cement surface although they are both at the same temperature. This is because e metal conducts heat away form the hand more quickly than cement which is a poor conductor.

Generally, substances which are liquids at ordinary temperatures are poor conductors. One exception is mercury which is a good conductor. Mercury is a metal in the liquid state at room temperature and pressure.

The thermal conductivity of gases is even lower than that of liquids.

How conduction works

Conduction takes place when heat energy is transferred from one particle to the next. When one end of a rod is heated, the particles at this end of the rod gain energy and vibrate more vigorously. These particles collide with their less energetic neighbours. Some of their energy is transferred to these neighbouring particles which in turn gain kinetic energy. In this way, heat energy is passed along the rod by the vibrating particles.

Conduction of heat in metals is far better than in other solids. The ‘free’ electrons in a metal are responsible for its superior thermal conductivity. When heated, the free electrons gain energy and move faster. These electrons are free to travel in the spaces between the particles before colliding with other electrons and transferring some of their energy to them .This process is much faster than the conduction by molecules in the body. Hence, metals conduct heat much faster than non-metals which have no free electrons.
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Convection