Electromagnetic radiation is a self-propagating wave with an electric and a magnetic component. Both components oscillate at right angles to each other and to the direction of propagation, and are in phase with each other.
Electromagnetic radiation is classified according to the frequency of this propagating wave: these types include, in order of increasing frequency, radio waves, microwaves, terahertz radiation, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays. Frequency is proportional to the energy of the wave, the higher the frequency the greater the energy. The wave's energy is equal to its frequency multiplied by Planck's constant). In some technical contexts the entire range of frequencies is referred to simplistically as "light".
Electromagnetic (EM) radiation carries energy and momentum, which may be imparted when it interacts with matter.
Electromagnetic waves of much lower frequency than visible light were first predicted by Maxwell's equations and subsequently discovered by Heinrich Hertz. Maxwell derived a wave form of the electric and magnetic equations, revealing the wavelike nature of electric and magnetic fields and their symmetry.
According to these equations, a time-varying electric field generates a magnetic field and vice versa. Therefore, as an oscillating electric field generates an oscillating magnetic field, the magnetic field in turn generates an oscillating electric field, and so on. These oscillating fields together form an electromagnetic wave.
Quantum theory provides a more sophisticated representation of electromagnetic
radiation wherein the context of the observation determines whether the wave is
considered to behave in this classical manner or in a particulate manner;
wave-particle duality.