Electromagnetic radiation is associated with oscillating electric and magnetic fields which are perpendicular to each other. It is a form of radiant energy which propagates through space in the form of waves. All electromagnetic radiations can travel through vacuum with the velocity of light. Its energy increases with its frequency and decreases with its wave length.
The arrangement of different electromagnetic radiations in the increasing order of their wave lengths or in the decreasing order of their frequencies is known as electromagnetic spectrum.
Low frequency /Radio / Microwaves/IR waves/Visiblelight/UV waves/X rays/Gamma rays / High energy
Visible region consist only a small portion of the total spectrum. Its wave length ranges between 3800 A* (Violet) to 7600 A* (red).
Particle nature of Electromagnetic radiation.
Phenomenon such as diffraction and interference can be explained on the basis of wave nature of electromagnetic radiation. But the phenomenon of photoelectric effect and black body radiation cannot be explained on the basis of wave theory. These properties can be explained on the basis of particle nature of electromagnetic radiation.