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Encyclopedia > Electromagnetic wave

Electromagnetic radiation is a propagating wave in space with electric and magnetic components. These components oscillate at right angles to each other. (In mathematical nomenclature, the electric and magnetic components are said to be each other's cross products.) A wave crashing against the shore A wave is a disturbance that propagates. ... Electricity is a property of certain subatomic particles (e. ... In physics, magnetism is a phenomenon by which materials exert an attractive or repulsive force on other materials. ... In mathematics, the cross product is a binary operation on vectors in vector space. ...


The term electromagnetic radiation is also used as a synonym for electromagnetic waves in general, even if they are not radiating or travelling in free space. This sense includes, for example, light travelling through an optical fiber, or electrical energy travelling within a coaxial cable. Electromagnetic radiation or EM radiation is a combination (cross product) of oscillating electric and magnetic fields perpendicular to each other, moving through space as a wave, effectively transporting energy and momentum. ... Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye, or in a more general sense, any electromagnetic radiation in the range from infrared to ultraviolet. ... Optical fibers An optical fiber is a transparent thin fiber, usually made of glass, for transmitting light. ... Coaxial cable is an electrical cable consisting of a round conducting wire, surrounded by an insulating spacer, surrounded by a cylindrical conducting sheath, and usually surrounded by a final insulating layer. ...


Electromagnetic radiation carries energy and momentum which may be imparted when it interacts with matter. In physics, momentum is a physical quantity related to the velocity and mass of an object. ... Matter is the substance of which a physical object is composed. ...

Contents


Physics

Theory

Electromagnetic waves were predicted by Maxwell's equations and subsequently discovered by Heinrich Hertz. Maxwell derived a wave form of the electric and magnetic equations which made explicit the wave nature of the electric and magnetic fields. These equations displayed the symmetry of the fields. Maxwells equations are the set of four equations, attributed to James Clerk Maxwell, that describe the behavior of both the electric and magnetic fields, as well as their interactions with matter. ... Heinrich Hertz Heinrich Rudolf Hertz (February 22, 1857 - January 1, 1894), was the German physicist for whom the hertz, the SI unit of frequency, is named. ...


According to the theory, a time-varying electric field generates a magnetic field and vice versa. Thus, an oscillating electric field creates an oscillating magnetic field, which in turn creates an oscillating electric field, and so on. By this means a EM wave is produced which propagates through space.


Properties

The electric and the magnetic fields exhibit the property of interference. This means that the field due a particular particle or time-varying electric or magnetic field adds to the fields due to other causes. (In physics this is the vector addition of all the individual electric and magnetic vectors.) As a result, EM radiation is influenced by various phenomena such as refraction and diffraction. For example, a travelling EM wave incident on a particular arrangement of atoms induces oscillation in the atoms and thus causes them to emit their own EM waves (called wavelets). These emissions interfere with the impinging wave and alter its form. Refraction in a Perspex (acrylic) block. ... Diffraction is the apparent bending and spreading of waves when they meet an obstruction. ... Properties For alternative meanings see atom (disambiguation). ... All wavelet transforms consider a function (taken to be a function of time) in terms of oscillations which are localized in both time and frequency. ...


In refraction, a wave moving from one medium to another of a different density changes its speed and direction when it enters the new medium. The ratio of the refractive indices of the media determines the extent of refraction. Refraction is the mechanism by which light disperses into a spectrum when it is shone through a prism. The electromagnetic spectrum encompasses all possible wavelengths of electromagnetic radiation. ...


The physics of electromagnetic radiation is electrodynamics, a subfield of electromagnetism. The willingness to question previously held truths and search for new answers resulted in a period of major scientific advancements, now known as the Scientific Revolution. ... Electromagnetism is the physics of the electromagnetic field: a field, encompassing all of space, composed of the electric field and the magnetic field. ... Electromagnetism is the physics of electromagnetic fields: a field, encompassing all of space, comprised of electrical and magnetic fields. ...


EM radiation exhibits both wave properties and particle properties (see wave-particle duality). These characteristics are mutually exclusive and appear separately in different circumstances: the wave characteristics appear when EM radation is measured over relatively larger timescales and over larger distances, and the particle characteristics are evident when measuring smaller distances and timescales. EM radiation's behaviours as a wave and as a stream of particles have been confirmed by a large number of experiments. In modern physics, duality most often refers to the paradigm underlying quantum mechanics, according to which matter or energy can exhibit properties associated with wave physics as well as classical particle mechanics. ...


Wave model

An important aspect of the wave nature of light is frequency. The frequency of a wave is its rate of oscillation and is measured in hertz, the SI unit of frequency, equal to one oscillation per second. Light usually comprises a spectrum of frequencies which sum to form the resultant wave. In addition, frequency affects properties like refraction, in which different frequencies undergo a different level of refraction. The hertz (symbol Hz) is the SI unit of frequency. ... The International System of Units (abbreviated SI from the French phrase, Système International dUnités) is the most widely used system of units. ... This article is about the unit of time. ...


Particle model

In the particle model of EM radiation, EM radiation is quantized as particles called photons. Quantisation of light represents the discrete packets of energy which constitute the radiation. The frequency of the radiation determines the magnitude of the energy of the particles. Moreover, these particles are emitted and absorbed by charged particles, so photons act as transporters of energy. The word quantum, pl. ... The photon can be perceived as a wave or a particle, depending on how it is measured In physics, the photon (from Greek φοτος, meaning light) is a quantum of the electromagnetic field, for instance light. ...


A photon absorbed by an atom excites an electron and elevates it to a higher energy level. If the energy is great enough, the electron is liberated from the atom in a process called ionisation. Conversely, an electron which descends to a lower energy level in an atom emits a photon of light equal to the energy difference. Ionisation can be: the process of creating an ion, see ionization a piece of music by Edgar Varèse; see Ionisation (Varèse) This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ...


The energy levels of electrons in atoms are discrete. Therefore, each element has its own characteristic frequencies.


Together these effects explain the absorption spectra of light. The dark bands in the spectrum are due to the atoms in the intervening medium which absorb different frequencies of the light. The composition of the medium through which the light travels determines the nature of the absorption spectrum. For instance, in a distant star, dark bands in the light it emits are due to the atoms in the atmosphere of the star. These bands correspond to the allowed energy levels in the atoms. A similar phenomenon occurs for emission. As the electrons descend to lower energy levels, a spectrum which represents the jumps between the energy levels of the electrons is exhibited. This is manifested in the emission spectrum of nebulae. The Triangulum Emission Nebula NGC 604 lies in a spiral arm of Galaxy M33, 2. ...


Speed of propagation


Any electric charge which accelerates, or any changing magnetic field, produces electromagnetic radiation. Electromagnetic information about the charge travels at the speed of light. Accurate treatment thus incorporates a concept known as retarded time (as opposed to advanced time, which is unphysical in light of causality), which adds to the expressions for the electrodynamic electric field and magnetic field. These extra terms are responsible for electromagnetic radiation. When any wire (or other conducting object such as an antenna) conducts alternating current, electromagnetic radiation is propagated at the same frequency as the electric current. Depending on the circumstances, it may behave as a wave or as particles. As a wave, it is characterized by a velocity (the speed of light), wavelength, and frequency. When considered as particles, they are known as photons, and each has an energy related to the frequency of the wave given by Planck's relation E = hν, where E is the energy of the photon, h = 6.626 × 10-34 J·s is Planck's constant, and ν is the frequency of the wave. The philosophical concept of causality or causation refers to the set of all particular causal or cause-and-effect relations. ... In physics, an electric field or E-field is an effect produced by an electric charge that exerts a force on charged objects in its vicinity. ... Current flowing through a wire produces a magnetic field (M) around the wire. ... A yagi antenna Most simply, an antenna is an electronic component designed to send or receive radio waves. ... An alternating current (AC) is an electrical current where the magnitude and direction of the current varies cyclically, as opposed to direct current, where the direction of the current stays constant. ... A wave crashing against the shore A wave is a disturbance that propagates. ... A particle is Look up Particle in Wiktionary, the free dictionary In particle physics, a basic unit of matter or energy. ... Cherenkov effect in a swimming pool nuclear reactor. ... The wavelength is the distance between repeating units of a wave pattern. ... Sine waves of various frequencies; the lower waves have higher frequencies than those above. ... The photon can be perceived as a wave or a particle, depending on how it is measured In physics, the photon (from Greek φοτος, meaning light) is a quantum of the electromagnetic field, for instance light. ... Max Planck This article is about Planck, the German physicist. ... Plancks constant, denoted h, is a physical constant that is used to describe the sizes of quanta. ...


One rule is always obeyed regardless of the circumstances. EM radiation in a vacuum always travels at the speed of light, relative to the observer, regardless of the observer's velocity. (This observation led to Albert Einstein's development of the theory of special relativity.) Cherenkov effect in a swimming pool nuclear reactor. ... Albert Einstein, by Yousuf Karsh Albert Einstein (March 14, 1879 – April 18, 1955) was a German theoretical physicist who is widely regarded as the greatest scientist of the 20th century. ... A simple introduction to this subject is provided in Special relativity for beginners Special relativity(SR) or the special theory of relativity is the physical theory published in 1905 by Albert Einstein. ...


Electromagnetic spectrum

See main article: electromagnetic spectrum

Generally, EM radiation is classified by wavelength into electrical energy, radio, microwave, infrared, the visible region we perceive as light, ultraviolet, X-rays and gamma rays. The electromagnetic spectrum encompasses all possible wavelengths of electromagnetic radiation. ... Electrical energy or Electromagnetic energy is a form of energy present in any electric field or magnetic field, or in any volume containing electromagnetic radiation. ... This page is about the radiation; for the appliance, see microwave oven. ... Image of a small dog taken in mid-infrared (thermal) light (false color) Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than visible light, but shorter than microwave radiation. ... The optical spectrum (light or visible spectrum) is the portion of the electromagnetic spectrum that is visible to the human eye. ... Ultraviolet (UV) radiation is electromagnetic radiation of a wavelength shorter than that of the visible region, but longer than that of soft X-rays. ... In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz... This article is about electromagnetic radiation. ...


The behavior of EM radiation depends on its wavelength. Higher frequencies have shorter wavelengths, and lower frequencies have longer wavelengths. When EM radiation interacts with single atoms and molecules, its behavior depends on the amount of energy per quantum it carries.


Spectroscopy can detect a much wider region of the EM spectrum than the visible range of 400 nm to 700 nm. A common laboratory spectroscope can detect wavelengths from 2 nm to 2500 nm. More in-depth information about the physical properties of objects, gases, or even stars can be obtained from this type of device. It is widely used in astrophysics. For example, many hydrogen atoms emit radio waves which have a wavelength of 21.12 cm. Spectroscopy is the study of spectra, that is, the dependence of physical quantities on frequency. ... Spiral Galaxy ESO 269-57 Astrophysics is the branch of astronomy that deals with the physics of the universe, including the physical properties (luminosity, density, temperature and chemical composition) of astronomical objects such as stars, galaxies, and the interstellar medium, as well as their interactions. ... General Name, Symbol, Number Hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1 (IA), 1, s Density, Hardness 0. ... Properties For alternative meanings see atom (disambiguation). ... The word emission generally means sending something out. ... Radio frequency, or RF, refers to that portion of the electromagnetic spectrum in which electromagnetic waves can be generated by alternating current fed to an antenna. ... The wavelength is the distance between repeating units of a wave pattern. ... A centimetre (American spelling: centimeter, symbol: cm) is an SI unit of length. ...


Light

See main article: light

EM radiation with a wavelength between 400 nm and 700 nm is detected by the human eye and perceived as visible light. Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye, or in a more general sense, any electromagnetic radiation in the range from infrared to ultraviolet. ... The wavelength is the distance between repeating units of a wave pattern. ... A nanometre (American spelling: nanometer, symbol: nm) is 1. ... Binomial name Homo sapiens Linnaeus, 1758 Subspecies Homo sapiens idaltu (extinct) Homo sapiens sapiens Human beings define themselves in biological, social, and spiritual terms. ... An eye is an organ that detects light. ... Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye, or in a more general sense, any electromagnetic radiation in the range from infrared to ultraviolet. ...


If radiation having a frequency in the visible region of the EM spectrum shines on an object, say a bowl of fruit, this results in our visual perception identifying information from the scene. Our brain's visual system processes the multitude of reflected frequencies into different shades and hues, and through this not-entirely-explained "psychophysical phenomenon," most humans perceive a bowl of fruit. Visual perception is one of the senses, consisting of the ability to detect light and interpret (see) it as the perception known as sight or naked eye vision. ...


In the vast majority of cases, however, the information carried by light is not directly apprehensible by human senses. Natural sources produce EM radiations across the spectrum; so, too, can human technology manipulate a broad range of wavelengths. Optical fiber transmits light which, although not suitable for direct viewing, can carry data. Those data can be translated into sound or even into an image. The coded form of such data is similar to that used with radio waves. Optical fibers An optical fiber is a transparent thin fiber, usually made of glass, for transmitting light. ...


Radio waves

See main article: radio wave

Radio waves carry information by varying amplitude and by varying frequency within a frequency band. Radio frequency, or RF, refers to that portion of the electromagnetic spectrum in which electromagnetic waves can be generated by alternating current fed to an antenna. ... Radio frequency, or RF, refers to that portion of the electromagnetic spectrum in which electromagnetic waves can be generated by alternating current fed to an antenna. ...


When EM radiation impinges upon a conductor, it couples to the conductor, travels along it, and induces an electric current on the surface of that conductor. This effect (the skin effect) is used in antennas. EM radiation may also cause certain molecules to absorb energy and thus to heat up; this is exploited in microwave ovens. En [ [ ciencia ] ] y [ [ ingeniería ] ], los conductores son los materiales de los cuales contenga las cargas movibles [ [ electricidad ] ]. Cuando una diferencia potencial eléctrica se impresiona a través de puntos separados en un conductor, las cargas móviles dentro del conductor se fuerzan para moverse, y una corriente eléctrica entre esos puntos aparece... Radio frequency induction or RF induction is an electrical phenomenon in which an electromagnetic wave passing through a conductor causes electric current to flow through it. ... The skin effect is the tendency of an alternating electric current to distribute itself within a conductor so that the current density near the surface of the conductor is greater than that at its core. ... Microwave oven A microwave oven is a kitchen appliance employing microwave radiation primarily to cook or heat food. ...


See also

The electromagnetic spectrum encompasses all possible wavelengths of electromagnetic radiation. ... Electromagnetic radiation can be classified into ionizing radiation and non-ionizing radiation, based on whether it is capable of ionizing atoms and breaking chemical bonds. ... Radiant energy is the energy transported by electromagnetic waves. ... Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye, or in a more general sense, any electromagnetic radiation in the range from infrared to ultraviolet. ... In telecommunications and warfare, the term electromagnetic pulse (EMP) has the following meanings: The electromagnetic radiation from an explosion (especially nuclear explosions) or an intensely fluctuating magnetic field caused by Compton-recoil electrons and photoelectrons from photons scattered in the materials of the electronic or explosive device or in a... Control of electromagnetic radiation is a national operational plan to minimize the use of electromagnetic radiation in the United States and its possessions and the Panama Canal Zone in the event of attack or imminent threat thereof, as an aid to the navigation of hostile aircraft, guided missiles, or other...

External links

  • Conversion of frequency to wavelength and back - electromagnetic, radio and sound waves
  • The Science of Spectroscopy - supported by NASA, includes OpenSpectrum, a Wiki-based learning tool for spectroscopy that anyone can edit

  Results from FactBites:
 
Electromagnetic Wave Transmission (821 words)
Electromagnetic wave transmission is the transmission of electrical energy by wires, the broadcasting of radio signals, and the phenomenon of visible light are all examples of the propagation of electromagnetic energy.
An electromagnetic wave does not penetrate far into an electrical conductor, and a wave that is incident on the surface of a good conductor is largely reflected.
The waves emitted from a source are oscillatory and are described in terms of frequency of oscillation.
  More results at FactBites »

 
 

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