Black body radiation|कृष्ण विकिरण प्रभाव

 Black body effect  

Hello friends! Today we are concern about Black body effect . 

This topic is very useful for understanding about Black body effect and it's perameters.

When radiant energy falls on a body, a part of it is reflected, a part continues into the interior of the body and is absorbed, and the third part is transmitted by the body. A body whose absorptivity is unity for all wavelengths is called an ideal black body or simply a black body or we can say that a body which absorbs all the incident radiations completely, irrespective of wavelength falling on it, reflecting none and transmitting none is called a black body. The other characteristic of such a body is that when heated to a suitable high temperature it emits total radiation. A black body is only an ideal conception and Lamp black is the nearest approach to such a body (Lamp black reflects about 1% of the incident radiation). Platinum black is another such a body.

It is found that as the temperature of a body is raised, the colour emitted by it becomes richer in waves of shorter length. For example, the colour of blackened platinum appears dull red at about 525°C, cherry red at about 900°C, orange red at 1100°C, yellow 1250°C and white at about 1600°C. The problem of distribution of energy among the wavelengths emitted by black body. when heated to different temperatures, was investigated by Lummer and Pringsheim in 1899 They used an electrically heated chamber with a small aperture as black body whose temperature was measured by a thermocouple. The arrangement is shown in figure . S is a slit placed at the focal plane of concave mirror M. Hence radiation from a black body was reflected as a parallel beam from this mirror. Radiations are dispersed by a prism P of rock salt or fluorspar placed on the turn table of a spectrometer. They are now focused on the bolometer with the help of another cancave mirror M,. The bolometer is connected to a sensitive galvanometer. The turn table is rotated alowly so that each part of the spectrum is focused successively on the bolometer and the deflection of the galvanometer is proportional to the intensity of each line. The wavelength at different portions of the spectrum was calculated by the formula for the dispersion of the material of the prism. By determining the intensity for various wavelengths in the whole spectrum of black body radiation, a a graph is drawn between intensity and wavelength. The body was raised to different temperatures and the distribution curve for each was drawn. The results are shown in fig. It is observed that: 

(1)as the temperature of the body rises, the intensity of radiation for each wavelength increases.

(2) for any one temperature, energy is distributed continuously among the various wavelengths and is maximum for a particular wavelength. The point of maximum energy shifts towards the shorter wavelengths as the temperature increased. 

(3) the total energy of radiation for given temperature is represented by the area between the curve and the horizontal axis. The area increases according to the fourth power of absolute temprature.

In next blog we are concern about ..

Stefen boltzmann law .

Thanks for reading ..place a commant if you like article.