Heat (Thermal) Energy and Heat Transfer


Radiation is the transfer of heat energy by electromagnetic radiation and specifically speaking that by infra red radiation. All objects whether hot or cold radiate heat energy (infra red radiations). The hotter the object the more heat energy it radiates. All objects also receive radiation and the exchange of radiant energy is a continuous process. Therefore a body at constant temperature is receiving and radiating energy at the same rate.

Infra red radiation is an electromagnetic radiation and so can travel through a vacuum, thus radiation unlike conduction and convection does not require particles for its propagation. It is for this reason we can receive heat energy from the sun.

The heating lamp transfers heat energy directly via infra red radiation.



The amount of radiation given out by objects depends on their temperature and their surface. The hotter the object the more energy it radiates and the bigger the heat difference between the hot object and the surroundings the faster the heat transfer.

Dull dark matt surfaces are good absorbers and good emitters of radiation. For example the cooling fins on the back of a refrigerator.

Light, shiny surfaces are poor absorbers and poor emitters of radiation.  This is why it is best to wear bright white clothes on a hot day as they reflect the heat and reduce absorption of the heat energy.