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Encyclopedia > Faraday effect

In physics, the Faraday effect or Faraday rotation is a magneto-optical phenomenon, or an interaction between light and a magnetic field. The rotation of the plane of polarization is proportional to the intensity of the component of the magnetic field in the direction of the beam of light. The first few hydrogen atom electron orbitals shown as cross-sections with color-coded probability density. ... Hahahahahahahahahahahahhahahahahahahahahahahahahahahahahahahahahahhahaahahhhahhhahaahhhahahahahahahahahahahahahahahahahahahahahahahahahahahahhahahahahahaahhaaahahahahahahahahahahahahhahahahahahahahhahahahahahahahahahahahahahahahahhahahahahahhahahahhahahahhahahahahahhahahahhahahahhahahahhahahahahahahahahahhahahaahhaahahhaahhahaahahahahhahaahahsahahahahahshhsshshshagagaggagagagagagaggagagahahahahhahahahahahahahahahahahahhahahahahahahahahhahahahahahahahahahahyhahahahahhahaahahahahahahahahahahhahahahaah! your moma is a hoe. ... In physics, magnetism is a phenomenon by which materials exert an attractive or repulsive force on other materials. ... In electrodynamics, polarization (also spelled polarisation) is the property of electromagnetic waves, such as light, that describes the direction of their transverse electric field. ...

The Faraday effect, a type of magneto-optic effect, discovered by Michael Faraday in 1845, was the first experimental evidence that light and magnetism are related. The theoretical basis for that relation, now called electromagnetic radiation, was developed by James Clerk Maxwell in the 1860s and 1870s. This effect occurs in most optically transparent dielectric materials (including liquids) when they are subject to strong magnetic fields. A magneto-optic effect is any one of a number of phenomena in which an electromagnetic wave interacts with a magnetic field, or with matter under the influence of a magnetic field. ... Michael Faraday, FRS (September 22, 1791 – August 25, 1867) was an English chemist and physicist (or natural philosopher, in the terminology of that time) who contributed significantly to the fields of electromagnetism and electrochemistry. ... Electromagnetic radiation can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. ... James Clerk Maxwell (13 June 1831 – 5 November 1879 in Edinburgh, Scotland) was an important mathematical physicist, who formulated a set of equations — eponymically named Maxwells equations — that expressed the basic laws of electricity and magnetism. ... Transparent glass ball In optics, transparency is the property of allowing light to pass. ... A dielectric, or electrical insulator, is a substance that is highly resistant to electric current. ... To meet Wikipedias quality standards, this article may require cleanup. ...

The Faraday effect is a result of ferromagnetic resonance when the permeability of a material is represented by a tensor. This resonance causes waves to be decomposed into two circularly polarized rays which propagate at different speeds, a property known as circular birefringence. The rays can be considered to re-combine upon emergence from the medium, however owing to the difference in propagation speed they do so with a net phase offset, resulting in a rotation of the angle of linear polarization. Ferromagnetism is a phenomenon by which a material can exhibit a spontaneous magnetization, and is one of the strongest forms of magnetism. ... // In physics, resonance is the tendency of a system to oscillate with high amplitude when excited by energy at a certain frequency. ... Permeability has several meanings: In electromagnetism, permeability is the degree of magnetisation of a material in response to a magnetic field. ... In mathematics, a tensor is (in an informal sense) a generalized linear quantity or geometrical entity that can be expressed as a multi-dimensional array relative to a choice of basis; however, as an object in and of itself, a tensor is independent of any chosen frame of reference. ... A calcite crystal laid upon a paper with some letters showing the double refraction Birefringence, or double refraction, is the decomposition of a ray of light into two rays (the ordinary ray and the extraordinary ray) when it passes through certain types of material, such as calcite crystals, depending on... To meet Wikipedias quality standards, this article or section may require cleanup. ...

There are a few applications of Faraday rotation in measuring instruments. For instance, the Faraday effect has been used to measure optical rotatory power, for amplitude modulation of light, and for remote sensing of magnetic fields.

The relation between the angle of rotation of the polarization and the magnetic field in a diamagnetic material is:

Polarization rotation due to the Faraday effect
beta = mathcal{V}Bd

where Image File history File links Faraday-effect. ...

β is the angle of rotation (in radians)
B is the magnetic flux density in the direction of propagation (in teslas)
d is the length of the path (in metres) where the light and magnetic field interact
mathcal{V} is the Verdet constant for the material. This empirical proportionality constant (in units of radians per tesla per metre) varies with wavelength and temperature and is tabulated for various materials.

A positive Verdet constant corresponds to L-rotation (anticlockwise) when the direction of propagation is parallel to the magnetic field and to R-rotation (clockwise) when the direction of propagation is anti-parallel. Thus, if a ray of light is passed through a material and reflected back through it, the rotation doubles. The radian is a unit of plane angle. ... The tesla (symbol T) is the SI derived unit of magnetic flux density (or magnetic induction). ... The metre, or meter (U.S.), is a measure of length. ... The Verdet constant is an optical constant that describes the strength of the Faraday effect for a particular material. ...

Some materials, such as terbium gallium garnet (TGG) have extremely high Verdet constants (≈ −40 rad T-1 m-1). By placing a rod of this material in a strong magnetic field, Faraday rotation angles of over 0.78 rad (45°) can be achieved. This allows the construction of Faraday rotators, which are the principal component of Faraday isolators, devices which transmit light in only one direction. The metre, or meter (U.S.), is a measure of length. ... A Faraday rotator is an optical device that rotates the polarization of light due to the Faraday effect. ... A Faraday isolator or optical isolator is an optical component which allows the transmission of polarised light in only one direction. ...

Similar isolators are constructed for microwave systems by using ferrite rods in a waveguide with a surrounding magnetic field. Ferrite may refer to: Ferrite (magnet)s (e. ... Look up waveguide in Wiktionary, the free dictionary. ...


Faraday rotation in the interstellar medium

The Faraday effect is imposed on light over the course of its propagation from its origin to the Earth, through the interstellar medium. Here, the effect is caused by free electrons and can be characterized as a difference in the refractive index seen by the two circularly polarized propagation modes. Hence, in contrast to the Faraday effect in solids or liquids, interstellar Faraday rotation has a simple dependence on the wavelength of light (λ), namely: Earth (IPA: , often referred to as the Earth, Terra, the World or Planet Earth) is the third planet in the solar system in terms of distance from the Sun, and the fifth largest. ... The distribution of ionized hydrogen (known by astronomers as H II (aitch two) from old spectroscopic terminology) in the parts of the Galactic interstellar medium visible from the Earths northern hemisphere (from the Wisconsin H-Alpha Mapper Survey) In astronomy, the interstellar medium (or ISM) is the matter (interstellar... Properties The electron (also called negatron, commonly represented as e−) is a subatomic particle. ... The refractive index (or index of refraction) of a material is the factor by which the phase velocity of electromagnetic radiation is slowed in that material, relative to its velocity in a vacuum. ...

beta = mathrm{RM} lambda^2 ,

where the overall strength of the effect is characterized by RM, the rotation measure. This in turn depends on B, and the number density of electrons, ne, both of which may vary along the propagation path, to give:

mathrm{RM} = frac{e^3}{2pi m^2c^4}int_0^d n_e B ;mathrm{d}s,


e is the charge of an electron
m is the mass of an electron
c is the speed of light in a vacuum

Faraday rotation is an important tool in astronomy for the measurement of magnetic fields, which can be estimated from rotation measures given a knowledge of the electron number density. In the case of radio pulsars, the dispersion caused by these electrons results in a time delay between pulses received at different wavelengths, which can be measured in terms of the electron column density, or dispersion measure. A measurement of both the dispersion measure and the rotation measure therefore yields the weighted mean of the magnetic field along the line of sight. The same information can be obtained from objects other than pulsars, if the dispersion measure can be estimated based on reasonable guesses about the propagation path length and typical electron densities. Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interactions. ... Unsolved problems in physics: What causes anything to have mass? Mass is a property of a physical object that quantifies the amount of matter and energy it is equivalent to. ... The speed of light in a vacuum is an important physical constant denoted by the letter c for constant or the Latin word celeritas meaning swiftness. It is the speed of all electromagnetic radiation in a vacuum, not just visible light. ... A giant Hubble mosaic of the Crab Nebula, a supernova remnant. ... Composite Optical/X-ray image of the Crab Nebula pulsar, showing surrounding nebular gases stirred by the pulsars magnetic field and radiation. ... Dispersion of a light beam in a prism. ...

Radio waves passing through the Earth's ionosphere are also subject to Faraday rotation; as the above equation indicates, the effect is proportional to the square of the wavelength. At 435 MHz (UHF), one should expect in the order of 1.5 complete rotations of the wavefront as it transits the ionosphere, whereas at 1.2 GHz less than a quarter of one rotation is likely. 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. ... Relationship of the atmosphere and ionosphere The ionosphere is the part of the atmosphere that is ionized by solar radiation. ...

Further reading

  • Optics, Eugene Hecht, Addison Wesley, 4th edition 2002, hardcover, ISBN 0-8053-8566-5, chapter 8.11.2
  • Optics Amnon Yariv, Oxford University Press; 5th edition (April 1997), hardcover, ISBN 0-19-510626-1, Optical Electronics in Modern Communications (Oxford Series in Electrical and Computer Engineering)
  • Propagation Effects on Satellite Systems at Frequencies Below 10GHz – A Handbook for Satellite Systems Design Flock, Warren L. NASA Reference Publication 1108(02) 1987. P 2-12 to 2-28.

See also

A Faraday rotator is an optical device that rotates the polarization of light due to the Faraday effect. ... This is a list of scientific phenomena and concepts named after people (eponymous phenomena). ... The inverse Faraday effect is the effect opposite to the Faraday effect. ... Quadratic Magnetic Rotation of Polarization of Light is called also QMR or QMR effect. ... The Voigt Effect, sometimes termed magnetic birefringence or magnetic double refreaction, is a magneto-optical phenomenon whereby the polarization of light may be rotated when passed through a vapor cell immersed in a magnetic field directed perpendicular to the beam direction. ...

External links

  Results from FactBites:
Faraday Crystals TGG and Glasses MOS-4 and MOS-10 (634 words)
Although the Faraday effect is not itself chromatic, the verdet constant itself is quite strongly a function of wavelength.
Faraday Isolators are passive unidirectional, non reciprocal devices that utilize the phenomenon of Magneto-Optic Rotation to isolate the source from reflections in an optical system.
Faraday Rotators are also used for example in ring laser systems to introduce a loss mechanism (in conjunction with some other intra-cavity polarization selective element) which is greater for one direction of propagation than for the other.
Faraday effect - Wikipedia, the free encyclopedia (855 words)
The rotation of the plane of polarization is proportional to the intensity of the component of the magnetic field in the direction of the beam of light.
The Faraday effect is a result of ferromagnetic resonance when the permeability of a material is represented by a tensor.
Faraday rotation is an important tool in astronomy for the measurement of magnetic fields, which can be estimated from rotation measures given a knowledge of the electron number density.
  More results at FactBites »



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