Transmission of Heat

When one end of a metal rod is heated, the unheated end soon becomes

warm. This is because heat travels through the metal by the process of

conduction.

All electrons are constantly vibrating and in metals the electrons are

mobile. When a metal is heated the kinetic energy of its electrons is

increased and they begin to move more rapidly and to move towards

the cooler parts of the metal. Hence their energy is transferred to the

cooler molecule.

In the process of convection heat is carried by and transferred by the

movement of a liquid of gas. When liquid is heated at the bottom of a

container a current of hot liquid moves upwards to be replaced by a

current of cold liquid moving down.

Radiation is the way in which heat travels from the sun across space to

the earth’s atmosphere. This “radiant energy” consists of invisible

electromagnetic waves, which are partly reflected and partly absorbed.

It comes from the sun directly or indirectly and when coming directly

travels through 150 million km of space.

Conduction and convection are methods of heat transfer which both

require a medium but radiation is a method of heat transfer, which

requires no medium.