The impulse p of the photon is equal to $p\; =\; E/C\; =\; H\; \backslash \; naked/c$.

The energy of the photons of an electromagnetic wave is preserved at the time of the crossing of various transparent mediums (on the other hand, a certain proportion of photons can be absorptive).

In the vacuum, the electromagnetic radiation, and in particular the light, move at the speed of 299  792  458  m/S. This speed, called Speed of light and noted C , is one of the constant physics fundamental.

The wavelength is equal to:

$\backslash \; lambda\; =\; \backslash \; frac\; \{c\_\; \backslash \; naked\}\; \{\backslash \; naked\}$

$c\_\; \backslash \; nu$ being speed of light in the medium considered for the frequency ν, with $c\_\; \backslash \; naked\; =\; c/n\_\; \backslash \; nu$ ($n\_\; \backslash \; nu$ being the Index of refraction of the monochromatic light of frequency ν in the medium considered).

The observation, at the end of the 19th century, that speed of light in the vacuum does not depend on the reference frame led to the development of the theory of the restricted Relativité.

Properties

• Any body with an higher temperature with 0 Kelvin (Absolute zero, is -273,15 °C) emits an electromagnetic radiation called thermal radiation.
• a body which receives an electromagnetic radiation can reflect a part and absorb the remainder of it. Absorptive energy is converted into thermal energy and contributes to the increase in the temperature of this body.
• a particle in charge of strong energy emits an electromagnetic radiation:
• when it is deviated by a magnetic field: it is the Synchrotron radiation; this synchrotron radiation is used as source of x-rays for many experiments of physics and biology (lines of lights around a synchrotron);
• when it penetrates in a different medium: it is the “continuous radiation of braking”;
• the absorption of a photon can cause atomic transitions, i.e. to excite an atom whose energy increases by the modification of orbital of one of its electrons.
• When an excited atom returns in its fundamental state of energy, it emits a photon whose energy (and thus frequency) correspond to a difference between two states of energy of the atom.
• In the same field of the electromagnetic spectrum, the photons are able to form pairs electron-positron pair in the semiconductors (principle of the CCC). While recombining, the electron and the hole emit light (principle of the diodes).
• the nuclear reactions, like those of Fission, fusion and disintegration, are often accompanied by an emission of photons of great energy called rays γ.

Electromagnetic spectrum

See also: electromagnetic Spectrum

An electromagnetic spectrum is the decomposition of an electromagnetic radiation according to its wavelength, or, in an equivalent way, its frequency ( via the equation of propagation) or of the energy of its photons.

For historical reasons, the electromagnetic waves are indicated by various terms, according to the frequency bands (or wavelength). By decreasing wavelength, it is:

• the waves radio and the waves radar are produced by electric currents high frequency;

• the waves Infra-red S, the visible Light and the radiation Ultraviolet are produced by electronic transitions in the atoms, concerning the outer-shell electrons, like by the thermal radiation; the ultraviolet waves have effects on the skin (bronzing, sunstrokes, cancer of the skin);
• the x-rays are produced at the time of the electronic transitions. They for example are generated by Radioactivité (photons of fluorescence emitted at the time of the reorganization of the electronic procession of an atom), by braking of electrons (tube with x-rays) or by Synchrotron radiation (by deviation of electron beam relativists). Because of their low wavelength, they diffract on the crystals; hard x-rays correspond to photons of higher energy, and x-rays soft with photons of weaker energy;
• the γ radiation is produced by the radioactivity at the time of the de-energizing of a core. They thus are emitted in particular by radioactive materials and the nuclear reactors.

See too

• Photon
• Life and radiation

Physical phenomena

• electronic Transitions
• nuclear Transitions
• Antenna S

Applications

• anechoic Faraday screen room
• Room
• Laser Interaction radiation-matter
• S

External bonds

• Impact on health, the site of WHO
• electromagnetic Fields induced by the electric lines and health a summary by GreenFacts of a scientific report/ratio of the International Research Center on Cancer (IARC)
• Belgian BioElectro Magnetic Group - Electric fields and magnetic 50 Hz and health
• Hydro-Quebec - To include/understand the electric fields and magnetic
• '' Bio-Initiative Carryforward: In Rationale for has Biologically-based Public Exposure Standard for Electromagnetic Fields (ELF and RF) '', report/ratio of August 31st, 2007

Simple: Electromagnetic radiation Zh-min-nan: Tiān-chû-pho Zh-yue: 電磁波