Black Body Radiations.
Thermal Radiation:
When the body is heated ,it emits radiation called thermal Radiation.
The nature of radiation depends upon the temperature.All the bodies not only emit radiations but also absorb radiation from their surroundings.if a body is hotter than it's surrounding it emits more radiation than it absorbs and tend to cool. At low temperature,a body emits radiation which are of longer wavelength in invite infrared region .At high temperature,the proportion of short wavelength radiation increases.
Black Body and Black Body Radiation.
Ideal black body:
A body which absorbs all the radiations incident upon it ,is called a perfect black body .
How to get a black body :
Consider a non_reflecting object such as solid having a hollow cavity in it. It has a small hole and the radiation can enter or escape only through th hole . It is blackened with lamp black inside it to make it a good absorber. The radiation that enters ,is reflected from inside wall many time times and partly absorbed at each reflection untill none remain. Such a body is called is called black body . It is absorber as well as ideal radiator.
Black Bdy Radiation.
The radiations emitted from it are called cavity radiations, temperature radiation or black body radiations. The wavelength of emitted radiations decreases with the increase in temperature.
For example.
When Platinum wire s heated ,it appears
dull red at about 500°C
Chery red at 900°C
Orange red at 1100°C
Yellow at 1300°C
White at 1600°C
This shows that as the temperature raises ,the radiation become richer in shorter wavelength.