The various kinds of radiation from the very short wavelength (high frequency) cosmic rays to the very long wavelength (low frequency) electric waves (radio waves etc.), constitute the electromagnetic spectrum. These radiation differ in wavelength (or frequency), but travel with the same velocity equal to the velocity of light (= 3× 108 m/s) in vacuum.
Electromagnetic radiation is used
1. for studying the structure of materials,
2. in telecommunication,
3. In transmission of radio and TV programs, and
4. in medical field.