Radiation process does not need any material medium for heat transfer.
Term Radiation refers to the continuous emission of energy from surface of all bodies and this energy is called radiant energy.
Radiant energy is in the form of Electro Magnetic waves.
Radiant energy emitted by a surface depends on the temperature and nature of the surface.
All bodies whether they are solid, liquid or gas emit radiant energy.
Electromagnetic radiation radiations emitted by a body by virtue of increased temperature of a body are called thermal radiation.
Thermal radiation falling on a body can partly be absorbed and partly be reflected by the body and this absorption and reflection of radiation depends on the color of body.
Thermal radiation travels through vacuum on straight line and with the velocity of light.
Thermal radiations can be reflected and refracted.
Black Body Radiation
A body that absorbs all the radiation falling on it is called a black body.
Radiation emitted by black body is called Black Body radiation.
A black body is also called an ideal radiator.
For practical purpose black body can be considered as an enclosure painted black from inside and a small hole is made in the wall.
Once radiation enters the enclosure it has very little chance to come out of the hole and it gets absorbed after multiple reflections inside the enclosure.
