Emission and absorption of infrared radiation
All bodies (objects) emit and absorb Electromagnetic radiation emitted from a hot object.. They do this whatever their How warm or cold something is.. The hotter the body:
- the more infrared radiation it gives out in a given time
- the greater the proportion of emitted radiation is visible light
Black bodies
There are no known objects that are perfect at absorbing or emitting all the radiation, of every possible frequency, that may be directed at it. Some objects do, however, come close to this and these are referred to as "black bodies".
Jonny Nelson introduces an animated explanation of black body radiation
A perfect black body is a An idea that has not been tested or proved to be true or real. object. It would have these properties:
- it would absorb all the radiation that falls on it
- it would not There is a reflection when waves bounce off a surface. or A wave is passed across or through聽a material聽(medium), eg light waves are transmitted through air, glass and water. any radiation
An object that is good at absorbing radiation is also a good Materials that send out energy., so a perfect black body would be the best possible emitter of radiation.
Stars are considered to be black bodies because they are very good emitters of most wavelengths in the The different types of electromagnetic radiation, arranged in order of frequency or wavelength.. This suggests that stars also absorb most wavelengths. Whilst there are a few wavelengths that stars do not absorb or emit, this figure is very low, so they can be treated as black bodies. Planets and black holes are also treated as nearly perfect black bodies.
Poor absorbers and emitters
White and shiny silvery surfaces are the worst absorbers, as they reflect all visible light wavelengths. Poor absorbers are also poor emitters, and do not emit radiation as quickly as darker colours. Radiators in homes are usually painted white so that the infrared radiation is emitted gradually.