The term radiation is applied to the kinds of processes which transmit energy by means of electromagnetic waves. The amount of radiation mainly depends upon the nature of body, temperature of the body and type of surface of the body.

when the radiations are falling on a body, three things happen, i.e. a part of the radiations are absorbed by the body, a part of the radiations are reflected and the remaining radiations are transmitted through the body.

Thermal diffusivity is defined as the ratio of the thermal conductivity to the heat capacity of a material and it measures the ability of a material to conduct thermal energy relative to its ability to store thermal energy. Thermal diffusivity is a physical property of the material.