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Radiation is a process of heat transfer that will occur between two different body temperatures without a solid or a fluid medium as transmitting medium. The example of this process is electromagnetic waves where no medium is mandatory for its propagation.

Figure 1.1 Various modes of heat transfer.

All the electromagnetic waves are categorized in terms of wavelength and it travels at a rate of speed as light which is C = 2.998 × 10⁸ m/s.

Properties of emission: The emission radiation depends on the following aspects by a body:

 ✓ Surface temperature

 ✓ Nature of surface

 ✓ Radiation frequency/wavelength

The following are the important parameters to deal the emission properties that are noted as emissive power (E_b), monochromatic emissive power (E_bʎ), emissivity (€), radiation intensity, radiosity, density, and pressure.

Concept of Black Body

A black body is an object which absorbs all the energy radiation from outer atmosphere to its receiving surface. A black body is a perfect emitter. For a black body α = 1, α = 0, and τ = 0.

Black body is an ideal surface that has the following properties:

 ✓ Black body absorbs all incident radiation irrespective of wavelength and directions.

 ✓ At a prescribed temperature, it emits larger amount of thermal radiation.