Basics on Thermal Radiation
Thermal radiation is defined as the transfer of energy by means of electromagnetic radiation.
Radiation differs from conduction and convection, because both conduction and convection require a bulk material to carry the energy from one place to another.
In contrast, (electromagnetic) radiation does not require a medium in order to propagate – therefore it can move through vacuum.
Blackbody Radiation
Black surfaces are very good at radiating and absorbing energy, but are poor reflectors of thermal energy.
A black body defined as something that absorbs all the wavelengths of electromagnetic radiation that fall on it. A black body enclosure can be used for demonstrate the phenomenon experimentally.
When the enclosure is heated to high temperatures, radiation emerges from the cavity. The color from the radiation depends on the temperature of the enclosure.
The trend is that as temperature increases, the radiation moves from infrared to the visible region of the electromagnetic spectrum. The colour changes from red, yellow and eventually to white when the temperature increases.
(To be continued.)
by Ed Law
