Thermal Radiation Article Index for
Thermal 		Website Links For
Thermal 		 

Information About

Thermal Radiation
  CATEGORIES ABOUT THERMAL RADIATION
   
electromagnetic radiation
   
thermodynamics
   
SHOPPER'S DELIGHT
 
Shop For:  
Department
Price Minimum:
Price Maximum:
      



The emitted wave frequency of the thermal radiation is a probability distribution depending only on temperature, and for a genuine Black Body is given by Planck’s Law Of Radiation . Wein's Law gives the most likely frequency of the emitted radiation, and the Stefan-Boltzmann Law gives the heat intensity.


PROPERTIES


Thermal radiation is an important concept in Thermodynamics as it is responsible for heat exchange between objects, as warmer Bodies radiate more heat than colder ones. The play of energy exchange is characterized by the following equation:

\alpha+ ho+ au=1 \,

Here, \alpha \, represents spectral absorption factor, ho \, spectral reflection factor and au \, spectral transmission factor. All these elements depend also on the frequency \upsilon \,. The spectral absorption factor is sometimes called Emissivity , and is denoted \epsilon \,.

In a practical situation and room-temperature setting, objects lose a lot of energy due to thermal radiation. However, the energy lost by emitting Infrared heat is regained by absorbing the heat of surrounding objects.


FORMULA


Thermal radiation energy per unit of volume is thus given by u(\upsilon,T)d\upsilon \,, where:

u(\upsilon,T)= rac{8\pi h\upsilon^3}{c^3}\cdot rac1{e^ rac{h\upsilon}{k_BT}-1}

For a radiating body, integrating the above equation obtains the output in Watt s given by the Stefan-Boltzmann law, as:

W = \epsilon(\upsilon)\cdot\sigma AT^4

Here, \epsilon \, is an emissivity correction factor between 0 and 1. It is a practically useful term to account for the fact that the radiating body is not a perfect black body. Furthermore, the emissivity can be found to depend on the frequency \upsilon\,. Objects that appear white (reflective in the Visual Spectrum ) are found to be near perfect black bodies in the infrared spectrum, which is why most household radiators are painted white.

Further, the wavelength \lambda \,, for which the emission intensity is highest, is given by Wien's Law as:

\lambda_{max} = rac{b}{T}


CONSTANTS


Definitions of constants used in the above equations:


EXTERNAL LINKS