Wiktionary
n. Radiation (quantized as photons) consisting of oscillating electric and magnetic fields oriented perpendicularly to each other, moving through space.
WordNet
n. radiation consisting of waves of energy associated with electric and magnetic fields resulting from the acceleration of an electric charge [syn: electromagnetic wave, nonparticulate radiation]
Wikipedia
Electromagnetic radiation (EM radiation or EMR) is the radiant energy released by certain electromagnetic processes. Visible light is an electromagnetic radiation. Other familiar electromagnetic radiations are invisible to the human eye, such as radio waves, infrared light and X-rays.
Classically, electromagnetic radiation consists of electromagnetic waves, which are synchronized oscillations of electric and magnetic fields that propagate at the speed of light through a vacuum. The oscillations of the two fields are perpendicular to each other and perpendicular to the direction of energy and wave propagation, forming a transverse wave. Electromagnetic waves can be characterized by either the frequency or wavelength of their oscillations to form the electromagnetic spectrum, which includes, in order of increasing frequency and decreasing wavelength: radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays.
Electromagnetic waves are produced whenever charged particles are accelerated, and these waves can subsequently interact with any charged particles. EM waves carry energy, momentum and angular momentum away from their source particle and can impart those quantities to matter with which they interact. Quanta of EM waves are called photons, which are massless, but they are still affected by gravity. Electromagnetic radiation is associated with those EM waves that are free to propagate themselves ("radiate") without the continuing influence of the moving charges that produced them, because they have achieved sufficient distance from those charges. Thus, EMR is sometimes referred to as the far field. In this language, the near field refers to EM fields near the charges and current that directly produced them, specifically, electromagnetic induction and electrostatic induction phenomena.
In the quantum theory of electromagnetism, EMR consists of photons, the elementary particles responsible for all electromagnetic interactions. Quantum effects provide additional sources of EMR, such as the transition of electrons to lower energy levels in an atom and black-body radiation. The energy of an individual photon is quantized and is greater for photons of higher frequency. This relationship is given by Planck's equation E = hν, where E is the energy per photon, ν is the frequency of the photon, and h is Planck's constant. A single gamma ray photon, for example, might carry ~100,000 times the energy of a single photon of visible light.
The effects of EMR upon biological systems (and also to many other chemical systems, under standard conditions) depend both upon the radiation's power and its frequency. For EMR of visible frequencies or lower (i.e., radio, microwave, infrared), the damage done to cells and other materials is determined mainly by power and caused primarily by heating effects from the combined energy transfer of many photons. By contrast, for ultraviolet and higher frequencies (i.e., X-rays and gamma rays), chemical materials and living cells can be further damaged beyond that done by simple heating, since individual photons of such high frequency have enough energy to cause direct molecular damage.
Usage examples of "electromagnetic radiation".
The German physicist Heinrich Hertz in 1887 was the first to find that when electromagnetic radiation—.
In addition to the FTL drive, the aliens must possess a form of FTL communications system, able to pick up FTL emanations associated with normal electromagnetic radiation.
Our eyes have evolved to sense electromagnetic radiation of certain frequencies.
The electrons, electrically charged, were trapped by Earth's magnetic field, soaking up more and more energy from the radiation falling from space, and they moved ever faster--and at last gave up their energy as pulses of electromagnetic radiation.
The electromagnetic radiation from such a flare--visible light, radio waves, ultraviolet and X-rays--reaches the Earth's vicinity in about eight minutes.
It behaves like normal electromagnetic radiation except that we don't notice it.
So this universe must have become transparent to electromagnetic radiation.
Lasers obey the same inverse square law that all other electromagnetic radiation does, of course.