Explain Polarization


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Explain Polarization

the action of restricting the vibrations of a transverse wave, especially light, wholly or partially to one direction. The polarization of light incident upon a grating is defined by the orientation of its electric and magnetic fields relative to the plane of incidence, where the plane. Polarization of light in classical, nonlinear, and quantum optics (PW-POLAR)5 ECTS (englische explain the relevant topics of the lecture. apply the methods to.

Explain Polarization Über dieses Buch

division into two sharply contrasting groups or sets of opinions or beliefs. the action of restricting the vibrations of a transverse wave, especially light, wholly or partially to one direction. the action of causing something to acquire polarity. hyperborean.nu › technology › technology › polarization-definitions. The polarization of light incident upon a grating is defined by the orientation of its electric and magnetic fields relative to the plane of incidence, where the plane. He found the polarized component to be either perpendicular (positive polarization) or parallel (negative polarization) to the plane defined by the directions from. To explain the dispersion phenomena, it is necessary in the quantum theory to count on a scattering of light by atoms in their normal state. At the same time, this​.

Explain Polarization

Since we now define the plane ofpolarization in terms of the direction ofthe electric field vector, conid it be that the plane of polarization was defined differently in. Polarization of light in classical, nonlinear, and quantum optics (PW-POLAR)5 ECTS (englische explain the relevant topics of the lecture. apply the methods to. Cross polarization discrimination. Ionospheric depolarization, rain & ice depolarization. Polarization. The polarization of an electromagnetic wave is defined as.

The most light is transmitted when the two filters are oriented so they polarize light in the same direction.

The least light is transmitted when the filters are oriented at right angles to each other. Please check the box if you want to proceed. Risk assessment is the identification of hazards that could negatively impact an organization's ability to conduct business.

Risk management is the process of identifying, assessing and controlling threats to an organization's capital and earnings. A security operations center SOC is a command center facility for a team of IT professionals with expertise in information An incident response team is a group of IT professionals in charge of preparing for and reacting to any type of organizational Protected health information PHI , also referred to as personal health information, generally refers to demographic information, Telemedicine is the remote delivery of healthcare services, such as health assessments or consultations, over the Disaster recovery as a service DRaaS is the replication and hosting of physical or virtual servers by a third party to provide Cloud disaster recovery cloud DR is a combination of strategies and services intended to back up data, applications and other NVMe non-volatile memory express is a host controller interface and storage protocol created to accelerate the transfer speed A storage area network SAN is a dedicated high-speed network or subnetwork that interconnects and presents shared pools of Home Topics Networking Smart grid polarization wave polarization.

The effect of polarization on visible light can be striking. Anyone who has worn polarized sunglasses, or who has used polarizing filters in photography, knows how a clear sky polarizes sunlight.

Polarized sunglasses can reduce glare reflected from surfaces; this is useful under certain driving conditions and can also make it easier to see beneath the surface of a body of water.

In twisted nematic display s TN displays , polarizing filters are used in conjunction with a special liquid to brighten and darken regions of the display as external voltage s are applied.

This makes it possible to display alphanumeric characters in wristwatches, cell phones, and various other consumer electronic devices.

This was last updated in March Login Forgot your password? Forgot your password? No problem! Submit your e-mail address below. Now if one were to introduce a phase shift in between those horizontal and vertical polarization components, one would generally obtain elliptical polarization [12] as is shown in the third figure.

Thus is circular polarization created in practice, starting with linearly polarized light and employing a quarter-wave plate to introduce such a phase shift.

The result of two such phase-shifted components in causing a rotating electric field vector is depicted in the animation on the right. Note that circular or elliptical polarization can involve either a clockwise or counterclockwise rotation of the field.

These correspond to distinct polarization states, such as the two circular polarizations shown above. Of course the orientation of the x and y axes used in this description is arbitrary.

The choice of such a coordinate system and viewing the polarization ellipse in terms of the x and y polarization components, corresponds to the definition of the Jones vector below in terms of those basis polarizations.

One would typically choose axes to suit a particular problem such as x being in the plane of incidence.

Since there are separate reflection coefficients for the linear polarizations in and orthogonal to the plane of incidence p and s polarizations, see below , that choice greatly simplifies the calculation of a wave's reflection from a surface.

Moreover, one can use as basis functions any pair of orthogonal polarization states, not just linear polarizations. For instance, choosing right and left circular polarizations as basis functions simplifies the solution of problems involving circular birefringence optical activity or circular dichroism.

Consider a purely polarized monochromatic wave. If one were to plot the electric field vector over one cycle of oscillation, an ellipse would generally be obtained, as is shown in the figure, corresponding to a particular state of elliptical polarization.

Note that linear polarization and circular polarization can be seen as special cases of elliptical polarization.

A polarization state can then be described in relation to the geometrical parameters of the ellipse, and its "handedness", that is, whether the rotation around the ellipse is clockwise or counter clockwise.

Full information on a completely polarized state is also provided by the amplitude and phase of oscillations in two components of the electric field vector in the plane of polarization.

This representation was used above to show how different states of polarization are possible. The amplitude and phase information can be conveniently represented as a two-dimensional complex vector the Jones vector :.

The product of a Jones vector with a complex number of unit modulus gives a different Jones vector representing the same ellipse, and thus the same state of polarization.

The physical electric field, as the real part of the Jones vector, would be altered but the polarization state itself is independent of absolute phase.

The basis vectors used to represent the Jones vector need not represent linear polarization states i. In general any two orthogonal states can be used, where an orthogonal vector pair is formally defined as one having a zero inner product.

A common choice is left and right circular polarizations, for example to model the different propagation of waves in two such components in circularly birefringent media see below or signal paths of coherent detectors sensitive to circular polarization.

Regardless of whether polarization state is represented using geometric parameters or Jones vectors, implicit in the parameterization is the orientation of the coordinate frame.

This permits a degree of freedom, namely rotation about the propagation direction. When considering light that is propagating parallel to the surface of the Earth, the terms "horizontal" and "vertical" polarization are often used, with the former being associated with the first component of the Jones vector, or zero azimuth angle.

On the other hand, in astronomy the equatorial coordinate system is generally used instead, with the zero azimuth or position angle, as it is more commonly called in astronomy to avoid confusion with the horizontal coordinate system corresponding to due north.

Another coordinate system frequently used relates to the plane of incidence. This is the plane made by the incoming propagation direction and the vector perpendicular to the plane of an interface, in other words, the plane in which the ray travels before and after reflection or refraction.

The component of the electric field parallel to this plane is termed p-like parallel and the component perpendicular to this plane is termed s-like from senkrecht , German for perpendicular.

Polarized light with its electric field along the plane of incidence is thus denoted p-polarized , while light whose electric field is normal to the plane of incidence is called s-polarized.

P polarization is commonly referred to as transverse-magnetic TM , and has also been termed pi-polarized or tangential plane polarized.

S polarization is also called transverse-electric TE , as well as sigma-polarized or sagittal plane polarized.

Natural light, like most other common sources of visible light, is incoherent : radiation is produced independently by a large number of atoms or molecules whose emissions are uncorrelated and generally of random polarizations.

In this case the light is said to be unpolarized. This term is somewhat inexact, since at any instant of time at one location there is a definite direction to the electric and magnetic fields, however it implies that the polarization changes so quickly in time that it will not be measured or relevant to the outcome of an experiment.

A so-called depolarizer acts on a polarized beam to create one which is actually fully polarized at every point, but in which the polarization varies so rapidly across the beam that it may be ignored in the intended applications.

Unpolarized light can be described as a mixture of two independent oppositely polarized streams, each with half the intensity. At any particular wavelength, partially polarized light can be statistically described as the superposition of a completely unpolarized component and a completely polarized one.

That polarized component can be described in terms of a Jones vector or polarization ellipse, as is detailed above. However, in order to also describe the degree of polarization, one normally employs Stokes parameters see below to specify a state of partial polarization.

However, in practice there are cases in which all of the light cannot be viewed in such a simple manner due to spatial inhomogeneities or the presence of mutually incoherent waves.

So-called depolarization, for instance, cannot be described using Jones matrices. Such matrices were first used by Paul Soleillet in , although they have come to be known as Mueller matrices.

While every Jones matrix has a Mueller matrix, the reverse is not true. Mueller matrices are then used to describe the observed polarization effects of the scattering of waves from complex surfaces or ensembles of particles, as shall now be presented.

The Jones vector perfectly describes the state of polarization and phase of a single monochromatic wave, representing a pure state of polarization as described above.

However any mixture of waves of different polarizations or even of different frequencies do not correspond to a Jones vector. In so-called partially polarized radiation the fields are stochastic , and the variations and correlations between components of the electric field can only be described statistically.

One such representation is the coherency matrix : [20] : — The coherency matrix contains all second order statistical information about the polarization.

This matrix can be decomposed into the sum of two idempotent matrices, corresponding to the eigenvectors of the coherency matrix, each representing a polarization state that is orthogonal to the other.

An alternative decomposition is into completely polarized zero determinant and unpolarized scaled identity matrix components.

In either case, the operation of summing the components corresponds to the incoherent superposition of waves from the two components.

The latter case gives rise to the concept of the "degree of polarization"; i. The coherency matrix is not easy to visualize, and it is therefore common to describe incoherent or partially polarized radiation in terms of its total intensity I , fractional degree of polarization p , and the shape parameters of the polarization ellipse.

An alternative and mathematically convenient description is given by the Stokes parameters , introduced by George Gabriel Stokes in The relationship of the Stokes parameters to intensity and polarization ellipse parameters is shown in the equations and figure below.

Neglecting the first Stokes parameter S 0 or I , the three other Stokes parameters can be plotted directly in three-dimensional Cartesian coordinates.

For a given power in the polarized component given by. Often the total beam power is not of interest, in which case a normalized Stokes vector is used by dividing the Stokes vector by the total intensity S 0 :.

When the non-polarized component is not of interest, the Stokes vector can be further normalized to obtain. The overlap between any two polarization states is dependent solely on the distance between their locations along the sphere.

The IEEE defines RHCP using the right hand with thumb pointing in the direction of transmit, and the fingers showing the direction of rotation of the E field with time.

The rationale for the opposite conventions used by Physicists and Engineers is that Astronomical Observations are always done with the incoming wave traveling toward the observer, where as for most engineers, they are assumed to be standing behind the transmitter watching the wave traveling away from them.

In a vacuum , the components of the electric field propagate at the speed of light , so that the phase of the wave varies in space and time while the polarization state does not.

When an electromagnetic wave interacts with matter, its propagation is altered according to the material's complex index of refraction.

When the real or imaginary part of that refractive index is dependent on the polarization state of a wave, properties known as birefringence and polarization dichroism or diattenuation respectively, then the polarization state of a wave will generally be altered.

In such media, an electromagnetic wave with any given state of polarization may be decomposed into two orthogonally polarized components that encounter different propagation constants.

The Jones matrix due to passage through a transparent material is dependent on the propagation distance as well as the birefringence. The birefringence as well as the average refractive index will generally be dispersive , that is, it will vary as a function of optical frequency wavelength.

Media termed diattenuating or dichroic in the sense of polarization , in which only the amplitudes of the two polarizations are affected differentially, may be described using a Hermitian matrix generally multiplied by a common phase factor.

In fact, since any matrix may be written as the product of unitary and positive Hermitian matrices, light propagation through any sequence of polarization-dependent optical components can be written as the product of these two basic types of transformations.

In birefringent media there is no attenuation, but two modes accrue a differential phase delay. If linearly polarized light passes through a birefringent material, its state of polarization will generally change, unless its polarization direction is identical to one of those basis polarizations.

Since the phase shift, and thus the change in polarization state, is usually wavelength-dependent, such objects viewed under white light in between two polarizers may give rise to colorful effects, as seen in the accompanying photograph.

Circular birefringence is also termed optical activity , especially in chiral fluids, or Faraday rotation , when due to the presence of a magnetic field along the direction of propagation.

When linearly polarized light is passed through such an object, it will exit still linearly polarized, but with the axis of polarization rotated.

A combination of linear and circular birefringence will have as basis polarizations two orthogonal elliptical polarizations; however, the term "elliptical birefringence" is rarely used.

Examples for linear blue , circular red , and elliptical yellow birefringence are shown in the figure on the left.

The total intensity and degree of polarization are unaffected. If the path length in the birefringent medium is sufficient, the two polarization components of a collimated beam or ray can exit the material with a positional offset, even though their final propagation directions will be the same assuming the entrance face and exit face are parallel.

This is commonly viewed using calcite crystals , which present the viewer with two slightly offset images, in opposite polarizations, of an object behind the crystal.

It was this effect that provided the first discovery of polarization, by Erasmus Bartholinus in Media in which transmission of one polarization mode is preferentially reduced are called dichroic or diattenuating.

Like birefringence, diattenuation can be with respect to linear polarization modes in a crystal or circular polarization modes usually in a liquid. Devices that block nearly all of the radiation in one mode are known as polarizing filters or simply " polarizers ".

The output of an ideal polarizer is a specific polarization state usually linear polarization with an amplitude equal to the input wave's original amplitude in that polarization mode.

Power in the other polarization mode is eliminated. However, in many instances the more relevant figure of merit is the polarizer's degree of polarization or extinction ratio , which involve a comparison of g 1 to g 2.

In addition to birefringence and dichroism in extended media, polarization effects describable using Jones matrices can also occur at reflective interface between two materials of different refractive index.

These effects are treated by the Fresnel equations. Part of the wave is transmitted and part is reflected; for a given material those proportions and also the phase of reflection are dependent on the angle of incidence and are different for the s and p polarizations.

Therefore, the polarization state of reflected light even if initially unpolarized is generally changed. Any light striking a surface at a special angle of incidence known as Brewster's angle , where the reflection coefficient for p polarization is zero, will be reflected with only the s -polarization remaining.

This principle is employed in the so-called "pile of plates polarizer" see figure in which part of the s polarization is removed by reflection at each Brewster angle surface, leaving only the p polarization after transmission through many such surfaces.

The generally smaller reflection coefficient of the p polarization is also the basis of polarized sunglasses ; by blocking the s horizontal polarization, most of the glare due to reflection from a wet street, for instance, is removed.

In the important special case of reflection at normal incidence not involving anisotropic materials there is no particular s or p polarization.

Both the x and y polarization components are reflected identically, and therefore the polarization of the reflected wave is identical to that of the incident wave.

However, in the case of circular or elliptical polarization, the handedness of the polarization state is thereby reversed, since by convention this is specified relative to the direction of propagation.

But in the general case of reflection at a nonzero angle of incidence, no such generalization can be made. For instance, right-circularly polarized light reflected from a dielectric surface at a grazing angle, will still be right-handed but elliptically polarized.

Linear polarized light reflected from a metal at non-normal incidence will generally become elliptically polarized. These cases are handled using Jones vectors acted upon by the different Fresnel coefficients for the s and p polarization components.

Some optical measurement techniques are based on polarization. In many other optical techniques polarization is crucial or at least must be taken into account and controlled; such examples are too numerous to mention.

In engineering , the phenomenon of stress induced birefringence allows for stresses in transparent materials to be readily observed. As noted above and seen in the accompanying photograph, the chromaticity of birefringence typically creates colored patterns when viewed in between two polarizers.

As external forces are applied, internal stress induced in the material is thereby observed. Additionally, birefringence is frequently observed due to stresses "frozen in" at the time of manufacture.

This is famously observed in cellophane tape whose birefringence is due to the stretching of the material during the manufacturing process.

Ellipsometry is a powerful technique for the measurement of the optical properties of a uniform surface.

It involves measuring the polarization state of light following specular reflection from such a surface. This is typically done as a function of incidence angle or wavelength or both.

Since ellipsometry relies on reflection, it is not required for the sample to be transparent to light or for its back side to be accessible.

Ellipsometry can be used to model the complex refractive index of a surface of a bulk material. It is also very useful in determining parameters of one or more thin film layers deposited on a substrate.

Due to their reflection properties , not only are the predicted magnitude of the p and s polarization components, but their relative phase shifts upon reflection, compared to measurements using an ellipsometer.

A normal ellipsometer does not measure the actual reflection coefficient which requires careful photometric calibration of the illuminating beam but the ratio of the p and s reflections, as well as change of polarization ellipticity hence the name induced upon reflection by the surface being studied.

In addition to use in science and research, ellipsometers are used in situ to control production processes for instance. The property of linear birefringence is widespread in crystalline minerals , and indeed was pivotal in the initial discovery of polarization.

In mineralogy , this property is frequently exploited using polarization microscopes , for the purpose of identifying minerals.

See optical mineralogy for more details. Sound waves in solid materials exhibit polarization. Differential propagation of the three polarizations through the earth is a crucial in the field of seismology.

Horizontally and vertically polarized seismic waves shear waves are termed SH and SV, while waves with longitudinal polarization compressional waves are termed P-waves.

We have seen above that the birefringence of a type of crystal is useful in identifying it, and thus detection of linear birefringence is especially useful in geology and mineralogy.

Linearly polarized light generally has its polarization state altered upon transmission through such a crystal, making it stand out when viewed in between two crossed polarizers, as seen in the photograph, above.

Likewise, in chemistry, rotation of polarization axes in a liquid solution can be a useful measurement. In a liquid, linear birefringence is impossible, however there may be circular birefringence when a chiral molecule is in solution.

When the right and left handed enantiomers of such a molecule are present in equal numbers a so-called racemic mixture then their effects cancel out.

However, when there is only one or a preponderance of one , as is more often the case for organic molecules , a net circular birefringence or optical activity is observed, revealing the magnitude of that imbalance or the concentration of the molecule itself, when it can be assumed that only one enantiomer is present.

This is measured using a polarimeter in which polarized light is passed through a tube of the liquid, at the end of which is another polarizer which is rotated in order to null the transmission of light through it.

In many areas of astronomy , the study of polarized electromagnetic radiation from outer space is of great importance. Although not usually a factor in the thermal radiation of stars , polarization is also present in radiation from coherent astronomical sources e.

Apart from providing information on sources of radiation and scattering, polarization also probes the interstellar magnetic field via Faraday rotation.

It has been suggested that astronomical sources caused the chirality of biological molecules on Earth. Unpolarized light, after being reflected by a specular shiny surface, generally obtains a degree of polarization.

Polarizing sunglasses exploit this effect to reduce glare from reflections by horizontal surfaces, notably the road ahead viewed at a grazing angle.

Wearers of polarized sunglasses will occasionally observe inadvertent polarization effects such as color-dependent birefringent effects, for example in toughened glass e.

The polarized light from LCD monitors see below is very conspicuous when these are worn. Polarization is observed in the light of the sky , as this is due to sunlight scattered by aerosols as it passes through Earth's atmosphere.

The scattered light produces the brightness and color in clear skies. This partial polarization of scattered light can be used to darken the sky in photographs, increasing the contrast.

Polarizing filters use these effects to optimize the results of photographing scenes in which reflection or scattering by the sky is involved.

Sky polarization has been used for orientation in navigation. The Pfund sky compass was used in the s when navigating near the poles of the Earth's magnetic field when neither the sun nor stars were visible e.

It has been suggested, controversially, that the Vikings exploited a similar device the " sunstone " in their extensive expeditions across the North Atlantic in the 9th—11th centuries, before the arrival of the magnetic compass from Asia to Europe in the 12th century.

Related to the sky compass is the " polar clock ", invented by Charles Wheatstone in the late 19th century. The principle of liquid-crystal display LCD technology relies on the rotation of the axis of linear polarization by the liquid crystal array.

Light from the backlight or the back reflective layer, in devices not including or requiring a backlight first passes through a linear polarizing sheet.

That polarized light passes through the actual liquid crystal layer which may be organized in pixels for a TV or computer monitor or in another format such as a seven-segment display or one with custom symbols for a particular product.

The liquid crystal layer is produced with a consistent right or left handed chirality, essentially consisting of tiny helices.

This causes circular birefringence, and is engineered so that there is a 90 degree rotation of the linear polarization state. However, when a voltage is applied across a cell, the molecules straighten out, lessening or totally losing the circular birefringence.

On the viewing side of the display is another linear polarizing sheet, usually oriented at 90 degrees from the one behind the active layer. Therefore, when the circular birefringence is removed by the application of a sufficient voltage, the polarization of the transmitted light remains at right angles to the front polarizer, and the pixel appears dark.

With no voltage, however, the 90 degree rotation of the polarization causes it to exactly match the axis of the front polarizer, allowing the light through.

Intermediate voltages create intermediate rotation of the polarization axis and the pixel has an intermediate intensity.

Displays based on this principle are widespread, and now are used in the vast majority of televisions, computer monitors and video projectors, rendering the previous CRT technology essentially obsolete.

The use of polarization in the operation of LCD displays is immediately apparent to someone wearing polarized sunglasses, often making the display unreadable.

In a totally different sense, polarization encoding has become the leading but not sole method for delivering separate images to the left and right eye in stereoscopic displays used for 3D movies.

This involves separate images intended for each eye either projected from two different projectors with orthogonally oriented polarizing filters or, more typically, from a single projector with time multiplexed polarization a fast alternating polarization device for successive frames.

Polarized 3D glasses with suitable polarizing filters ensure that each eye receives only the intended image. Historically such systems used linear polarization encoding because it was inexpensive and offered good separation.

However circular polarization makes separation of the two images insensitive to tilting of the head, and is widely used in 3-D movie exhibition today, such as the system from RealD.

Projecting such images requires screens that maintain the polarization of the projected light when viewed in reflection such as silver screens ; a normal diffuse white projection screen causes depolarization of the projected images, making it unsuitable for this application.

Although now obsolete, CRT computer displays suffered from reflection by the glass envelope, causing glare from room lights and consequently poor contrast.

Several anti-reflection solutions were employed to ameliorate this problem. One solution utilized the principle of reflection of circularly polarized light.

A circular polarizing filter in front of the screen allows for the transmission of say only right circularly polarized room light.

With the right circular polarization filter placed in front of the reflecting glass, the unwanted light reflected from the glass will thus be in very polarization state that is blocked by that filter, eliminating the reflection problem.

The reversal of circular polarization on reflection and elimination of reflections in this manner can be easily observed by looking in a mirror while wearing 3-D movie glasses which employ left- and right-handed circular polarization in the two lenses.

Closing one eye, the other eye will see a reflection in which it cannot see itself; that lens appears black. However the other lens of the closed eye will have the correct circular polarization allowing the closed eye to be easily seen by the open one.

All radio and microwave antennas used for transmitting or receiving are intrinsically polarized. They transmit in or receive signals from a particular polarization, being totally insensitive to the opposite polarization; in certain cases that polarization is a function of direction.

Most antennas are nominally linearly polarized, but elliptical and circular polarization is a possibility. As is the convention in optics, the "polarization" of a radio wave is understood to refer to the polarization of its electric field, with the magnetic field being at a 90 degree rotation with respect to it for a linearly polarized wave.

The vast majority of antennas are linearly polarized.

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The best short-range communications is obtained when the transmitting and receiving source and destination antennas have the same polarization.

The least efficient short-range communications usually takes place when the two antennas are at right angles for example, one horizontal and one vertical.

Over long distances, the atmosphere can cause the polarization of a radio wave to fluctuate, so the distinction between horizontal and vertical becomes less significant.

Some wireless antennas transmit and receive EM waves whose polarization rotates degrees with each complete wave cycle.

This type of polarization, called elliptical or circular polarization, can be either clockwise or counterclockwise. The best communications results are obtained when the transmitting and receiving antennas have the same sense of polarization both clockwise or both counterclockwise.

The worst communications usually takes place when the two antennas radiate and receive in the opposite sense one clockwise and the other counterclockwise.

In ordinary visible light, there are numerous wave components at random polarization angles. When such light is passed through a special filter, the filter blocks all light except that having a certain polarization.

When two polarizing filters are placed so a ray of light passes through them both, the amount of light transmitted depends on the angle of the polarizing filters with respect to each other.

The most light is transmitted when the two filters are oriented so they polarize light in the same direction.

The least light is transmitted when the filters are oriented at right angles to each other. Please check the box if you want to proceed.

Risk assessment is the identification of hazards that could negatively impact an organization's ability to conduct business.

Risk management is the process of identifying, assessing and controlling threats to an organization's capital and earnings. A security operations center SOC is a command center facility for a team of IT professionals with expertise in information In the context of electricity, polarization is the process of separating opposite charges within an object.

The positive charge becomes separated from the negative charge. By inducing the movement of electrons within an object, one side of the object is left with an excess of positive charge and the other side of the object is left with an excess of negative charge.

Charge becomes separated into opposites. The polarization process always involves the use of a charged object to induce electron movement or electron rearrangement.

In the above diagram and accompanying discussion, electrons within a conducting object were induced into moving from the left side of the conducting can to the right side of the can.

Being a conductor, electrons were capable of moving from atom to atom across the entire surface of the conductor. But what if the object being polarized is an insulator?

Electrons are not free to move across the surface of an insulator. How can an insulator such as a wooden wall be polarized?

Polarization can occur within insulators, but the process occurs in a different manner than it does within a conductor. In a conducting object, electrons are induced into movement across the surface of the conductor from one side of the object to the opposite side.

In an insulator, electrons merely redistribute themselves within the atom or molecules nearest the outer surface of the object. To understand the electron redistribution process, it is important to take another brief excursion into the world of atoms, molecules and chemical bonds.

The electrons surrounding the nucleus of an atom are believed to be located in regions of space with specific shapes and sizes. The actual size and shape of these regions is determined by the high-powered mathematical equations common to Quantum Mechanics.

Rather than being located a specific distance from the nucleus in a fixed orbit, the electrons are simply thought of as being located in regions often referred to as electron clouds.

At any given moment, the electron is likely to be found at some location within the cloud. The electron clouds have varying density; the density of the cloud is considered to be greatest in the portion of the cloud where the electron has the greatest probability of being found at any given moment.

And conversely, the electron cloud density is least in the regions where the electron is least likely to be found. In addition to having varying density, these electron clouds are also highly distortable.

The presence of neighboring atoms with high electron affinity can distort the electron clouds around atoms.

Rather than being located symmetrically about the positive nucleus, the cloud becomes asymmetrically shaped. As such, there is a polarization of the atom as the centers of positive and negative charge are no longer located in the same location.

The atom is still a neutral atom; it has just become polarized. The discussion becomes even more complex and perhaps too complex for our purposes when we consider molecules - combination of atoms bonded together.

In molecules, atoms are bonded together as protons in one atom attract the electrons in the clouds of another atom. This electrostatic attraction results in a bond between the two atoms.

Electrons are shared by the two atoms as they begin to overlap their electron clouds. If the atoms are of different types for instance, one atom is Hydrogen and the other atom is Oxygen , then the electrons within the clouds of the two atoms are not equally shared by the atoms.

The clouds become distorted, with the electrons having the greatest probability of being found closest to the more electron-greedy atom.

The bond is said to be a polar bond. The distribution of electrons within the cloud is shifted more towards one atom than towards the other atom.

This is the case for the two hydrogen-oxygen bonds in the water molecule. Electrons shared by these two atoms are drawn more towards the oxygen atom than towards the hydrogen atom.

Subsequently, there is a separation of charge, with oxygen having a partially negative charge and hydrogen having a partially positive charge.

It is very common to observe this polarization within molecules. In molecules that have long chains of atoms bonded together, there are often several locations along the chain or near the ends of the chain that have polar bonds.

This polarization leaves the molecule with areas that have a concentration of positive charges and other areas with a concentration of negative charges.

This principle is utilized in the manufacture of certain commercial products that are used to reduce static cling.

The centers of positive and negative charge within the product are drawn to excess charge residing on the clothes. There is a neutralization of the static charge buildup on the clothes, thus reducing their tendency to be attracted to each other.

Other products actually use a different principle. During manufacturing, a thin sheet is soaked in a solution containing positively charged ions.

The sheet is tossed into the dryer with the clothes. Being saturated with positive charges, the sheet is capable of attracting excess electrons that are scuffed off of clothes during the drying cycle.

A complete discussion of the world of atoms, molecules and chemical bonds is beyond the scope of The Physics Classroom. Nonetheless, a model of the atom as a distortable cloud of negative electrons surrounding a positive nucleus becomes essential to understanding how an insulating material can be polarized.

If a charged object is brought near an insulator, the charges on that object are capable of distorting the electron clouds of the insulator atoms.

There is a polarization of the neutral atoms. As shown in the diagrams below, the neutral atoms of the insulator will orient themselves in such a manner as to place the more attractive charge nearest the charged object.

Once polarized in this manner, opposites can now attract. A common demonstration performed in class involved bringing a negatively charged balloon near a wooden door or wooden cabinet.

In the same manner, two Polaroid filters oriented with their polarization axes perpendicular to each other will block all the light.

Now that's a pretty cool observation that could never be explained by a particle view of light. Unpolarized light can also undergo polarization by reflection off of nonmetallic surfaces.

The extent to which polarization occurs is dependent upon the angle at which the light approaches the surface and upon the material that the surface is made of.

Metallic surfaces reflect light with a variety of vibrational directions; such reflected light is unpolarized. However, nonmetallic surfaces such as asphalt roadways, snowfields and water reflect light such that there is a large concentration of vibrations in a plane parallel to the reflecting surface.

A person viewing objects by means of light reflected off of nonmetallic surfaces will often perceive a glare if the extent of polarization is large.

Fishermen are familiar with this glare since it prevents them from seeing fish that lie below the water. Light reflected off a lake is partially polarized in a direction parallel to the water's surface.

Fishermen know that the use of glare-reducing sunglasses with the proper polarization axis allows for the blocking of this partially polarized light.

By blocking the plane-polarized light, the glare is reduced and the fisherman can more easily see fish located under the water. Polarization can also occur by the refraction of light.

Refraction occurs when a beam of light passes from one material into another material. At the surface of the two materials, the path of the beam changes its direction.

The refracted beam acquires some degree of polarization. Most often, the polarization occurs in a plane perpendicular to the surface.

The polarization of refracted light is often demonstrated in a Physics class using a unique crystal that serves as a double-refracting crystal. Iceland Spar, a rather rare form of the mineral calcite, refracts incident light into two different paths.

The light is split into two beams upon entering the crystal. Subsequently, if an object is viewed by looking through an Iceland Spar crystal, two images will be seen.

The two images are the result of the double refraction of light. Both refracted light beams are polarized - one in a direction parallel to the surface and the other in a direction perpendicular to the surface.

Since these two refracted rays are polarized with a perpendicular orientation, a polarizing filter can be used to completely block one of the images.

If the polarization axis of the filter is aligned perpendicular to the plane of polarized light, the light is completely blocked by the filter; meanwhile the second image is as bright as can be.

And if the filter is then turned degrees in either direction, the second image reappears and the first image disappears. Now that's pretty neat observation that could never be observed if light did not exhibit any wavelike behavior.

Polarization also occurs when light is scattered while traveling through a medium. When light strikes the atoms of a material, it will often set the electrons of those atoms into vibration.

The vibrating electrons then produce their own electromagnetic wave that is radiated outward in all directions. This newly generated wave strikes neighboring atoms, forcing their electrons into vibrations at the same original frequency.

These vibrating electrons produce another electromagnetic wave that is once more radiated outward in all directions.

This absorption and reemission of light waves causes the light to be scattered about the medium. This process of scattering contributes to the blueness of our skies, a topic to be discussed later.

This scattered light is partially polarized. Polarization by scattering is observed as light passes through our atmosphere.

The scattered light often produces a glare in the skies. Photographers know that this partial polarization of scattered light leads to photographs characterized by a washed-out sky.

The problem can easily be corrected by the use of a Polaroid filter. As the filter is rotated, the partially polarized light is blocked and the glare is reduced.

The photographic secret of capturing a vivid blue sky as the backdrop of a beautiful foreground lies in the physics of polarization and Polaroid filters.

Polarization has a wealth of other applications besides their use in glare-reducing sunglasses.

In industry, Polaroid filters are used to perform stress analysis tests on transparent plastics. As light passes through a plastic, each color of visible light is polarized with its own orientation.

If such a plastic is placed between two polarizing plates, a colorful pattern is revealed. As the top plate is turned, the color pattern changes as new colors become blocked and the formerly blocked colors are transmitted.

A common Physics demonstration involves placing a plastic protractor between two Polaroid plates and placing them on top of an overhead projector.

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