Different Types of Radiations and Their Sources

Electromagnetic spectra may be emission or absorption spectrum on the basis of energy absorbed or emitted. An emission spectrum is obtained when a substance emits radiation after absorbing energy. An absorption spectra is obtained when a substance absorbs certain wavelengths and leave dark spaces in bright continuous spectrum.
Electromagnetic wave theory was successful in explaining the properties of light such as interference. diffraction etc., but it could not explain the following
1. Black body radiation
2. Photoelectric effect
These phenomena could be explained only if electromagnetic waves are supposed to have particle nature.
1. Black Body Radiation
If the substance being heated is a black body. the radiation emitted is called black body radiation.
2. Photoelectric Effect
It is the phenomenon in which beam of light of certain frequency falls on the surface of metal and electrons are ejected from it.
This phenomenon is known as photoelectric effect. It was first observed by Hertz.
Wo< = hvo
Wo< = hc / λmax
Threshold frequency (vo) = minimum frequency of the radiation
Work function (Wo) = required minimum energy of the radiation
E = KE + Wo
∴ 1 / 2 mv2 = h(v – vo)
[Kinetic energy of ejected electron = h(v – vo)
where; v = frequency of incident radiation
vo = threshold frequency