Explain The Concept Of Radiation?

Radiation is the third process of heat transfer after conduction  and convection. Unlike conduction and convection, radiation does not require a material medium for heat transfer. It can take place in a vacuum. For example heat from the sun reaches the earth by the process of radiation.

Conduction or convection is not possible because of the vacuum between the sun and the earth. The sun emits electromagnetic waves of different frequencies and the wavelengths but with the same speed in vacuum.

Light is only part of this spectrum of electromagnetic waves. The part of the spectrum that makes us feel warm is the infra-red waves (or infra red radiation). Heat due to the infra-red waves is called radiant heat. Besides the sun, hot objects like a hot iron emit some radiant heat. The hotter the object, the greater the amount of radiant heat emitted.

Infra red radiation is absorbed by all objects and surfaces. The absorption causes a temperature rise. Infra red radiation is emitted by all objects and surfaces. This emission causes the temperature to fall.

In general it has been noticed, a good emitter of radiant heat is also a good absorber of radiant heat. Conversely, a poor emitter of radiant heat is also a poor absorber of radiant heat.