electromagnetic radiation

Electromagnetic radiation (EM radiation or EMR or just radiation) is radiation such as light, radio waves, etc. (Much of the dangerous radiation associated with radioactivity is not EMR: much EMR is ubiquitous and harmless in everyday life.) EMR is termed "electromagnetic" because the waves consist of changing electric fields and magnetic fields that are interacting in a way that causes the location of the changes to travel. (Analogously, water waves consist of a kind of change in water level, in which the location of the water-level changing travels.) When experiment and theory revealed the nature of electric fields and magnetic fields, it was evident that they could form waves, and deliberate attempts to produce such waves by manipulating fields produced what we call radio waves. These waves showed properties like those of light (such as the same speed, i.e., c), acting exactly as if light and radio waves are the same thing, except for their frequency. Overall classifications within the electromagnetic spectrum (based on frequency ranges):

• gamma rays (GR) (highest frequency, with shortest wavelengths)
• X-rays
• ultraviolet (UV)
• visible light
• infrared (IR)
• radio (lowest frequency, with longest wavelengths)

For more detail, see electromagnetic spectrum and the Wavelengths Table.