The energy radiated by a hot body depends on the nature of the radiating surface. A black body absorbs all the radiations falling on it and emits radiation that are independent of the shape, size, material and nature of the surface selected for the body and depends on its temperature.
A black body is an ideal abstraction and cannot be realised in practice. For rough work, we use surface coated with lamp-black or platinum black; but for more accurate work, black body designed by Fery is used.
Fery constructed an enclosure having a hole. The hole O should be placed against the conical projection P of the enclosure and the enclosure should be coated black from inside. Any radiation falling on the hole passes through it and is completely absorbed due to successive reflections.
When we heat the enclosure, the black-body radiations come out from the hole and not the enclosure, that acts as a black body. A black-body is most convenient reference for the study of radiation emitted by hot bodies.
