Heat And Thermodynamics

Black Body

A black body absorbs all the radiations incident upon it. All wavelengths/frequencies are infact, absorbed.

A black body is a good absorber, good emitter, a bad reflector and a bad transmitter. Its absorptive coefficient is unity if the black body is ideal. In case of perfectly black body, coefficients of reflection and transmission are zero.

When heated to a high temperature, an ideal black body emits radiations of all wavelengths/frequencies.

An ideal black body need not be blcak in colour.

The black body radiations are also known as white radiations because it emits all radiations when heated to a high temperature.

The radiations from a black body depend upon its temperature only. These heat radiations do not depend on density, mass, size or the nature of the body.

The emission spectrum of an ideal black body is a continuous spectrum. Hence all bodies in nature emitting continuous spectrum are black bodies. Sun or a lamp of high power are thus black bodies giving continuous spectrum.

Lamp black is 96% black ad platinum black ia about 98% black.

Wien's black body and Ferry's black body are considered to be almost black. A fine hole in a double walled spherical cavity, evacuated and painted black, represents Ferry's black body.