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In physics, electromagnetic radiation (EMR) is the set of waves of an electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. [ 1 ] [ 2 ] Classically , electromagnetic radiation consists of electromagnetic waves , which are synchronized oscillations of electric and magnetic fields .
There are various mathematical descriptions of the electromagnetic field that are used in the study of electromagnetism, one of the four fundamental interactions of nature. In this article, several approaches are discussed, although the equations are in terms of electric and magnetic fields, potentials, and charges with currents, generally ...
A diagram of the electromagnetic spectrum, showing various properties across the range of frequencies and wavelengths. The electromagnetic spectrum is the full range of electromagnetic radiation, organized by frequency or wavelength. The spectrum is divided into separate bands, with different names for the electromagnetic waves within each band.
In an extreme case, roughly 90% of 667.5 cm −1 photons are absorbed within 1 meter by 400 ppm of CO 2 at surface density, [23] but they are replaced by emission of an equal number of 667.5 cm −1 photons. The radiation field thereby maintains the blackbody intensity appropriate for the local temperature.
Continuous charge distribution. The volume charge density ρ is the amount of charge per unit volume (cube), surface charge density σ is amount per unit surface area (circle) with outward unit normal nĚ‚, d is the dipole moment between two point charges, the volume density of these is the polarization density P.
The existence of electromagnetic radiation was proved by Heinrich Hertz in a series of experiments ranging from 1886 to 1889 in which he discovered the existence of radio waves. The full electromagnetic spectrum (in order of increasing frequency) consists of radio waves, microwaves , infrared radiation , visible light , ultraviolet light , X ...
Like other electromagnetic waves, a radio wave has a property called polarization, which is defined as the direction of the wave's oscillating electric field perpendicular to the direction of motion. A plane-polarized radio wave has an electric field that oscillates in a plane perpendicular to the direction of motion.
Radiant intensity is used to characterize the emission of radiation by an antenna: [2], = (), where E e is the irradiance of the antenna;; r is the distance from the antenna.; Unlike power density, radiant intensity does not depend on distance: because radiant intensity is defined as the power through a solid angle, the decreasing power density over distance due to the inverse-square law is ...